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Ketamine has much support in the use of hard-to-treat depression and suicidal behaviors. Below are studies and their links, including a meta-analysis, which demonstrate the effect of Ketamine. Also a recent trial by Carlos Zarate shows the heterogenous nature of response to Ketamine . It is difficult to say who is going to be lifted from their depression completely or partially respond, but in the study, Dr. Zarate showed that patients with a long history of suicidal thinking and self-harm will have less of a response in some cases.

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Intravenous ketamine may rapidly reduce suicidal thinking in depressed patients << Article link 

Intravenous ketamine may rapidly reduce suicidal thinking in depressed patients

Repeat intravenous treatment with low doses of the anesthetic drug ketamine quickly reduced suicidal thoughts in a small group of patients with treatment-resistant depression. In their report receiving Online First publication in the Journal of Clinical Psychiatry, a team of Massachusetts General Hospital (MGH) investigators report the results of their study in depressed outpatients who had been experiencing suicidal thought for three months or longer.

“Our finding that low doses of ketamine, when added on to current antidepressant medications, quickly decreased suicidal thinking in depressed patients is critically important because we don’t have many safe, effective, and easily available treatments for these patients,” says Dawn Ionescu, MD, of the Depression Clinical and Research Program in the MGH Department of Psychiatry, lead and corresponding author of the paper. “While several previous studies have shown that ketamine quickly decreases symptoms of depression in patients with treatment-resistant depression, many of them excluded patients with current suicidal thinking.”

It is well known that having suicidal thoughts increases the risk that patients will attempt suicide, and the risk for suicide attempts is 20 times higher in patients with depression than the general population. The medications currently used to treat patients with suicidal thinking — including lithium and clozapine — can have serious side effects, requiring careful monitoring of blood levels; and while electroconvulsive therapy also can reduce suicidal thinking, its availability is limited and it can have significant side effects, including memory loss.

Primarily used as a general anesthetic, ketamine has been shown in several studies to provide rapid relief of symptoms of depression. In addition to excluding patients who reported current suicidal thinking, many of those studies involved only a single ketamine dose. The current study was designed not only to examine the antidepressant and antisuicidal effects of repeat, low-dose ketamine infusions in depressed outpatients with suicidal thinking that persisted in spite of antidepressant treatment, but also to examine the safety of increased ketamine dosage.

The study enrolled 14 patients with moderate to severe treatment-resistant depression who had suicidal thoughts for three months or longer. After meeting with the research team three times to insure that they met study criteria and were receiving stable antidepressant treatment, participants received two weekly ketamine infusions over a three-week period. The initial dosage administered was 0.5 mg/kg over a 45 minute period — about five times less than a typical anesthetic dose — and after the first three doses, it was increased to 0.75 mg/kg. During the three-month follow-up phase after the ketamine infusions, participants were assessed every other week.

The same assessment tools were used at each visit before, during and after the active treatment phase. At the treatment visits they were administered about 4 hours after the infusions were completed. The assessments included validated measures of suicidal thinking, in which patients were directly asked to rank whether they had specific suicide-related thoughts, their frequency and intensity.

While only 12 of the 14 enrolled participants completed all treatment visits — one dropped out because of ketamine side effects and one had a scheduling conflict — most of them experienced a decrease in suicidal thinking, and seven achieved complete remission of suicidal thoughts at the end of the treatment period. Of those seven participants, two maintained remission from both suicidal thinking and depression symptoms throughout the follow-up period. While there were no serious adverse events at either dose and no major differences in side effects between the two dosage levels, additional studies in larger groups of patients are required before any conclusions can be drawn.

“In order to qualify for this study, patients had to have suicidal thinking for at least three months, along with persistent depression, so the fact that they experienced any reduction in suicidal thinking, let alone remission, is very exciting,” says Ionescu, who is an instructor in Psychiatry at Harvard Medical School. “We only studied intravenous ketamine, but this result opens the possibility for studying oral and intranasal doses, which may ease administration for patients in suicidal crises.”

She adds, “One main limitation of our study was that all participants knew they were receiving ketamine. We are now finishing up a placebo-controlled study that we hope to have results for soon. Looking towards the future, studies that aim to understand the mechanism by which ketamine and its metabolites work for people with suicidal thinking and depression may help us discover areas of the brain to target with new, even better therapeutic drugs.”

 

Rapid and Sustained Reductions in Current Suicidal Ideation Following Repeated Doses of Intravenous Ketamine: Secondary Analysis of an Open-Label Study  << Article in Clinical Psychiatry

Ketamine for Rapid Reduction of Suicidal Thoughts in Major Depression: A Midazolam-Controlled Randomized Clinical Trial Article link for below:

Ketamine was significantly more effective than a commonly used sedative in reducing suicidal thoughts in depressed patients, according to researchers at Columbia University Medical Center (CUMC). They also found that ketamine’s anti-suicidal effects occurred within hours after its administration.

The findings were published online last week in the American Journal of Psychiatry.

According to the Centers for Disease Control and Prevention, suicide rates in the U.S. increased by 26.5 percent between 1999 and 2015.

“There is a critical window in which depressed patients who are suicidal need rapid relief to prevent self-harm,” said Michael Grunebaum, MD, a research psychiatrist at CUMC, who led the study. “Currently available antidepressants can be effective in reducing suicidal thoughts in patients with depression, but they can take weeks to have an effect. Suicidal, depressed patients need treatments that are rapidly effective in reducing suicidal thoughts when they are at highest risk. Currently, there is no such treatment for rapid relief of suicidal thoughts in depressed patients.”

Most antidepressant trials have excluded patients with suicidal thoughts and behavior, limiting data on the effectiveness of antidepressants in this population. However, previous studies have shown that low doses of ketamine, an anesthetic drug, causes a rapid reduction in depression symptoms and may be accompanied by a decrease in suicidal thoughts.

The 80 depressed adults with clinically significant suicidal thoughts who enrolled in this study were randomly assigned to receive an infusion of low-dose ketamine or midazolam, a sedative. Within 24 hours, the ketamine group had a clinically significant reduction in suicidal thoughts that was greater than with the midazolam group. The improvement in suicidal thoughts and depression in the ketamine group appeared to persist for up to six weeks.

Those in the ketamine group also had greater improvement in overall mood, depression, and fatigue compared with the midazolam group. Ketamine’s effect on depression accounted for approximately one-third of its effect on suicidal thoughts, suggesting the treatment has a specific anti-suicidal effect.

Side effects, mainly dissociation (feeling spacey) and an increase in blood pressure during the infusion, were mild to moderate and typically resolved within minutes to hours after receiving ketamine.

“This study shows that ketamine offers promise as a rapidly acting treatment for reducing suicidal thoughts in patients with depression,” said Dr. Grunebaum. “Additional research to evaluate ketamine’s antidepressant and anti-suicidal effects may pave the way for the development of new antidepressant medications that are faster acting and have the potential to help individuals who do not respond to currently available treatments.”

Ketamine for Rapid Reduction of Suicidal Thoughts in major depression – A midazolam controlled trial PDF article

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Ketamine as a Potential Treatment for Suicidal Ideation A Systematic Review of the Literature 2015

Abstract
Objective To review the published literature on the efficacy
of ketamine for the treatment of suicidal ideation (SI).
Methods The PubMed and Cochrane databases were
searched up to January 2015 for clinical trials and case
reports describing therapeutic ketamine administration to
patients presenting with SI/suicidality. Searches were also
conducted for relevant background material regarding the
pharmacological function of ketamine.
Results Nine publications (six studies and three case
reports) met the search criteria for assessing SI after
administration of subanesthetic ketamine. There were no
studies examining the effect on suicide attempts or death
by suicide. Each study demonstrated a rapid and clinically
significant reduction in SI, with results similar to previously
described data on ketamine and treatment-resistant
depression. A total of 137 patients with SI have been
reported in the literature as receiving therapeutic ketamine.
Seven studies delivered a dose of 0.5 mg/kg intravenously
over 40 min, while one study administered a 0.2 mg/kg
intravenous bolus and another study administered a liquid
suspension. The earliest significant results were seen after
40 min, and the longest results were observed up to
10 days postinfusion.
Conclusion Consistent with clinical research on ketamine
as a rapid and effective treatment for depression, ketamine
has shown early preliminary evidence of a reduction in
depressive symptoms, as well as reducing SI, with minimal
short-term side effects. Additional studies are needed to
further investigate its mechanism of action, long-term
outcomes, and long-term adverse effects (including abuse)
and benefits. In addition, ketamine could potentially be
used as a prototype for further development of rapid-acting
antisuicidal medication with a practical route of administration
and the most favorable risk/benefit ratio.
Key Points
Preliminary data from randomized controlled trials
have demonstrated that ketamine may rapidly and
effectively control treatment-resistant depression,
though the effects are transient.
A small subset of studies has demonstrated similar
results in the effects of ketamine on suicidal ideation.
Ketamine has potential as a rapid treatment for
suicidal ideation and/or a possible model compound
for future drug development.

4 Discussion
With an estimated prevalence of mood disorders ranging
from 3.3 to 21.4 % and the substantially increased risk of
suicide among patients with mood disorders, treatment is
certainly warranted [19]. Current treatment options for
suicidality are limited. They include brain stimulation
therapeutics, such as ECT, and pharmacological intervention
(lithium, clozapine). The efficacy of lithium in treating
suicidality has been documented [20, 21] and has recently been reviewed and pooled in a recent meta-analysis of 48
studies [22]. Clozapine has also been shown to reduce
suicide risk in patients with schizophrenia [23, 24]. The
limitations of both lithium and clozapine include a longer
time to efficacy in this psychiatric emergency/urgency,
compared with the early response to ketamine [25]. Ketamine
seems to be gaining substantial evidence as a pharmacological
option for depression with a fast onset of
action, but its long-term effects need further investigation.
In addition, ketamine probably offers a faster onset of
action in terms of SI, but further work is certainly needed
in this area. Given the risk of suicide and even the
increasing rates of suicide in certain subgroups, such as
soldiers and veterans [26, 27], there is an urgent need for
faster therapeutics for SI and TRD. Importantly, suicidality
and suicide pose a high global burden of patient suffering
to families and society. Although several small-to-moderate
sized studies, in addition to several reviews, have been
published that have examined the efficacy of ketamine in
TRD, there are considerably fewer published data
specifically examining ketamine in patients presenting with
SI. Notably, only three studies have directly examined SI
as the primary outcome [11, 16, 17], while the rest
examined SI as the secondary outcome [4, 15, 18], not
including case reports. This review summarizes the current
published literature regarding ketamine as a treatment for
SI. The data so far show promising trends of ketamine
being an effective and rapid treatment with minimal side
effects.
Pharmacologically, ketamine is an N-methyl-D-aspartate
(NMDA) receptor antagonist. It has been used for anesthesia
in the USA since the 1970s. At subanesthetic doses,
ketamine has been shown to increase glutamate levels [3].
This mechanism is relevant, as glutamate regulation and
expression are altered in patients with major depressive
disorder (MDD). Studies have also demonstrated an
abnormal glutamate–glutamine–gamma-aminobutyric acid
cycle in patients with suicidality [28]. Furthermore, ketamine
has also been shown to work on nicotinic and opioid
receptors [29]. No other class of antidepressant medication
works to modulate the glutamatergic system, and research
continues into this, with the goal of characterizing the full
mechanism of action of ketamine and perhaps developing
other compounds that would have similar effects. Thus,
even if the approval and marketing of ketamine as a rapidacting
antisuicidal and antidepressant medication is not
realized, it could well be a prototype for development of
other medication(s) that retain the mechanism of action
with more favorable qualities and a lesser adverse effect
profile (such as a longer duration of action or less or no
addictive potential). Although the mechanisms explaining
the antisuicidal effect and the NMDA receptor antagonism
of ketamine are still unclear, some of the initial evidence
points to an anti-inflammatory action via the kynurenic
acid pathway. Strong suggestions as to the causal relationship
between inflammation and depression/suicidality
has come from studies demonstrating that cytokines [30,
31] and interferon-b [32] induce depression and suicidality.
Other recent studies have added to the notion of implicating
brain immune activation in the pathogenesis of suicidality.
For instance, one study showed microglial
activation of postmortem brain tissue in suicide victims
[33]. Another study found increased levels of the cytokine
interleukin-6 in cerebrospinal fluid from patients who had
attempted suicide [34]. Higher levels of inflammatory
markers have been shown in suicidal patients than in nonsuicidal
depressed patients [33, 35]. Inflammation leads to
production of both quinolinic acid (an NMDA agonist) and
kynurenic acid (a NMDA antagonist). An increased
quinolinic acid to kynurenic acid ratio leads to NMDA
receptor stimulation. The correlation between quinolinic
acid and Suicide Intent Scale scores indicates that changes
in glutamatergic neurotransmission could be specifically
linked to suicidality [36].
Small randomized controlled trials have demonstrated
the efficacy of ketamine in rapidly treating patients with
both TRD and/or bipolar depression [4, 8, 9, 11, 16–18].
Some studies have also examined suicide items as a secondary
measure in their depression rating scales [4, 7]. In
total, the studies examining ketamine and TRD have nearly
consistently demonstrated that ketamine provides relief
from depressive and suicidal symptoms, starting at 40 min
and lasting for as long as 5 days. Questions still remain as
to the long-term effects of this treatment, how much should
be administered and how often, any serious adverse effects,
and the mechanism of action.
Pharmacologically, ketamine has poor bioavailability
and is best administered via injection [37]. In their landmark
study, Berman et al. [4] found that a subanesthetic
dose (0.5 mg/kg) rapidly improved depressive symptoms.
Most of the subsequent studies have delivered ketamine as
a constant infusion for 40 min at a rate of 0.5 mg/kg.
Others have examined its efficacy after multiple infusions
and observed similar results [8, 13, 16, 38]. Currently, it is
recommended that ketamine be administered in a hospital
setting [39].

______________________________________

Characterizing the course of suicidal ideation response to ketamine

Characterizing the course of suicidal ideation response to ketamine PDF

2018 article from Carlos Zarate discussing the variable course outcomes with Ketamine for suicidality and correlations to serum markers and behavior and longevity of self-harm prior to treatment:

 

Background: : No pharmacological treatments exist for active suicidal ideation (SI), but the glutamatergic
modulator ketamine elicits rapid changes in SI. We developed data-driven subgroups of SI trajectories after
ketamine administration, then evaluated clinical, demographic, and neurobiological factors that might predict SI
response to ketamine.
Methods: : Data were pooled from five clinical ketamine trials. Treatment-resistant inpatients (n = 128) with
DSM-IV-TR-diagnosed major depressive disorder (MDD) or bipolar depression received one subanesthetic
(0.5 mg/kg) ketamine infusion over 40 min. Composite SI variable scores were analyzed using growth mixture
modeling to generate SI response classes, and class membership predictors were evaluated using multinomial
logistic regressions. Putative predictors included demographic variables and various peripheral plasma markers.
Results: : The best-fitting growth mixture model comprised three classes: Non-Responders (29%), Responders
(44%), and Remitters (27%). For Responders and Remitters, maximal improvements were achieved by Day 1.
Improvements in SI occurred independently of improvements in a composite Depressed Mood variable for
Responders, and partially independently for Remitters. Indicators of chronic SI and self-injury were associated
with belonging to the Non-Responder group. Higher levels of baseline plasma interleukin-5 (IL-5) were linked to
Remitters rather than Responders.
Limitations: : Subjects were not selected for active suicidal thoughts; findings only extend to Day 3; and plasma,
rather than CSF, markers were used.
Conclusion: : The results underscore the heterogeneity of SI response to ketamine and its potential independence
from changes in Depressed Mood. Individuals reporting symptoms suggesting a longstanding history of chronic
SI were less likely to respond or remit post-ketamine.

1. Introduction
Suicide poses a serious threat to public health. Worldwide, suicide
accounts for approximately 1 million deaths, and 10 million suicide
attempts are reported annually (World Health Organization, 2014). In
the United States, the national suicide rate has increased by approximately
28% over the last 15 years (Curtin et al., 2016). At the same
time, relatively few interventions for suicide risk exist. While treatments
such as clozapine and lithium have demonstrated effects on
suicidal behavior over weeks to months, these effects may be limited to
specific diagnoses (Cipriani et al., 2005; Griffiths et al., 2014). Currently,
no FDA-approved medications exist to treat suicidal ideation
(SI), leaving those who experience a suicidal crisis with limited options
for a reprieve of symptoms. Consequently, a critical need exists for
rapid-acting treatments that can be used in emergency settings.
A promising off-label agent for this purpose is the rapid-acting antidepressant
ketamine, which past studies have suggested reduces suicidal
thoughts (Diazgranados et al., 2010a; Murrough et al., 2015; Price
et al., 2009). A recent meta-analysis of 167 patients with a range of
mood disorder diagnoses found that ketamine reduced suicidal
thoughts compared to placebo as rapidly as within a few hours, with
effects lasting as long as seven days (Wilkinson et al., 2017). These
results are reinforced by newer findings of reduced active suicidal
ideation post-ketamine compared to a midazolam control(Grunebaum et al., 2018). As the efficacy literature develops in the era
of personalized medicine, two important issues must be addressed.
First, little is known about the acute course of SI following ketamine.
The speed with which antidepressant response occurs, and how much
improvement can be expected on average, has been documented for
single administrations of ketamine (Mathew et al., 2012; Sanacora
et al., 2017); in the limited available literature, researchers have
emulated previous studies examining antidepressant effect, where a
cutoff of 50% improvement demarcated response (Nierenberg and
DeCecco, 2001). Nevertheless, it remains unknown whether this categorization
accurately reflects the phenomenon of suicidal thoughts.
Empirically-derived approaches to the description of SI trajectory after
ketamine may be useful in operationalizing “response” in future clinical
trials.
Second, identifying demographic, clinical, or biological predictors
of SI response to ketamine would allow researchers and clinicians to
determine who is most likely to exhibit an SI response to ketamine. A
broad literature describes clinical and demographic predictors for suicide
risk (Franklin et al., 2017), and a smaller literature connects suicidal
thoughts and behaviors to plasma markers such as brain-derived
neurotrophic factor (BDNF) and cytokines (Bay-Richter et al., 2015;
Falcone et al., 2010; Isung et al., 2012; Serafini et al., 2017; Serafini
et al., 2013). However, no biomarkers have been shown to predict SI/
behavior response to intervention, a finding reinforced by the National
Action Alliance for Suicide Prevention’s Research Prioritization Task
Force’s Portfolio Analysis (National Action Alliance for Suicide
Prevention: Research Prioritization Task Force, 2015). Notably, predictor
analyses have the potential to reveal insights into personalized
treatments for suicidal individuals, as well as the neurobiology of SI
response. With respect to antidepressant response, for example, this
approach yielded the observation that individuals with a family history
of alcohol dependence may be more likely to exhibit an antidepressant
response to ketamine (Krystal et al., 2003; Niciu et al., 2014; PermodaOsip
et al., 2014).
The goals of this study were to elucidate trajectories of SI response
and identify predictors of that response, with the ultimate goal of
adding to the growing literature surrounding ketamine’s specific effects
on SI. In particular, we sought to determine whether the heterogeneous
patterns of change in SI after ketamine administration were better explained
by a model with two or more latent groups of trajectories rather
than a single average trajectory, using secondary analyses from previously
published clinical trials. These classes were then used to evaluate
potential clinical, demographic, and plasma biomarker predictors
of SI response to ketamine in order to generate hypotheses.. Discussion
This analysis used a data-driven approach to characterize SI response
to ketamine. The data were best explained by three trajectory
classes: one with severe average baseline SI and little to no response to
ketamine (Non-Responders), one with moderate average baseline levels
of SI and significant response to ketamine (Responders), and a third
with moderate average baseline levels of SI and complete remission of
SI by two days post-ketamine (Remitters). These findings suggest a
diversity of post-ketamine changes in SI that may not be captured under
traditional methods of categorizing response to treatment.
Furthermore, we found evidence that SI response and antidepressant
response could be distinguished from each other; one subset of participants
experienced improvement in SI that was partially explained by
improvements in Depressed Mood, while the other group’s improvements
in SI occurred independently of antidepressant response. With
regard to predictors of SI response trajectory, preliminary results suggest
the individuals least likely to experience improvement in SI postketamine
were those with the most severe SI and a history of self-injury.
Few plasma markers emerged as predictors of SI response in this study,
highlighting the limitations of connecting SI ratings of response with
biological markers.
The growth mixture modeling approach used here underscored the
heterogeneity of SI response to ketamine, which would not have been
captured by simply calculating the average trajectory. The class assignment
from this approach also differed from the definition of response
(50% reduction in symptoms) traditionally used in the antidepressant
literature, which often focuses on a specific timepoint rather
than the entire symptom trajectory. In comparing classification using a
50% response at Day 1 and Day 3 with the latent trajectory classes, we
found representation of almost every SI class across each responder
group, highlighting the potential limitations of the 50% response approach.
Further study is needed to determine which of these approaches
will prove more fruitful. Complete remission of SI has previously been
used as an outcome measure in clinical trials and in a meta-analysis of
ketamine’s efficacy (Grunebaum et al., 2017; Grunebaum et al., 2018;
Wilkinson et al., 2017), as well as in a study examining the relationship
between SI response to ketamine and changes in nocturnal wakefulness
(Vande Voort et al., 2017). One strength of the present study is that this
data-driven approach provides classifications that directly reflect the
phenomena under study as they are, as opposed to what they should be.
Especially when used in larger samples than the current study, this
approach is particularly promising in its ability to provide a more
nuanced understanding of the nature of SI response to ketamine.
Our results also support the idea that SI response in particular can target. First, it should be noted here that SI classes were not distinguishable
by baseline Depressed Mood scores; patients with the most
severe SI did not differ meaningfully in Depressed Mood scores from
those with the mildest SI. Second, while previous analyses of these data
documented that BMI and family history of alcohol dependence predicted
antidepressant response (Niciu et al., 2014), SI response was not
associated with these variables in the current analysis. Third, the antidepressant
response profiles of the SI classes suggest that SI response
and antidepressant response are not wholly redundant. This aligns with
previous clinical trials and meta-analytic reviews of the literature suggesting
that SI response to ketamine occurs partially independently of
antidepressant response (Grunebaum et al., 2018; Wilkinson et al.,
2017). Nevertheless, this independence did not hold true across both SI
response groups. Specifically, antidepressant and SI response were
clearly linked in Remitters, with depression accounting for half of the
changes in SI; however, in Responders, improvements in SI occurred
independently from improvements in Depressed Mood. These discrepancies
could be related to ketamine’s complex neurobiological
mechanisms or to the potentially low levels of clinical severity observed
in the Remitters.
Interestingly, the current analyses found no baseline demographic
variables that reliably distinguished Responders from Remitters. Some
phenotypic characteristics were uniquely associated with belonging to
the Non-Responder group, suggesting that a long-standing history of
self-injury or SI may indicate resistance to rapid changes in SI.
Relatedly, a recent, randomized clinical trial of repeat-dose ketamine
compared to placebo found that ketamine had no effect on SI in a
sample of patients selected for their longstanding, chronic history of SI
(Ionescu, 2017). These results highlight the importance of patient selection,
particularly for suicide risk. It should be stressed, however, that
SI does not necessarily translate to suicidal attempts or deaths; to our
knowledge, no study has yet linked ketamine with reduced risk of
suicidal behavior. Indeed, in the present study the SI Non-Responders
experienced limited antidepressant effects in response to ketamine, but
may nevertheless have improved on other, unmeasured symptoms that
could provide important benefit and relief. As the ketamine literature
develops, it will be important to identify which clinical symptom profiles
are most likely to have a robust anti-SI and anti-suicidal behavior
response to ketamine and which ones may benefit from other interventions.
While we evaluated a range of potential plasma markers previously
linked to suicidal ideation and behavior, in the present analysis only IL5
was associated with the SI Responder subgroup. Ketamine is known to
have anti-inflammatory effects (Zunszain et al., 2013), but the relationship
between antidepressant response and change in cytokine
levels remains unclear (Park et al., 2017). Cytokines have been linked
to suicidal behavior in the past; a recent meta-analysis found that lower
levels of IL-2 and IL-4, and higher levels of TGFbeta, were associated
with suicidal thoughts and behaviors (Serafini et al., 2013); however, toour knowledge IL-5 has not previously been linked to SI. Given the large
number of comparisons and lack of precedent in the literature, this
result may have been spurious and should be interpreted with caution.
A number of other results may reflect meaningful relationships, but the
high degree of variability—and the associated wide confidence intervals—suggests
that larger sample sizes are needed to better elucidate
the nature of any such relationships (e.g. baseline VEGF: χ2 = 6.13,
p = .05, but OR (95% CI) 13.33 (0.93–200.00)). Somewhat surprisingly,
plasma BDNF levels were not associated with responder class.
Previous studies of bipolar, but not MDD, samples found that plasma
BDNF levels were associated with SI response after ketamine
(Grunebaum, 2017; Grunebaum et al., 2017), suggesting that the mixed
diagnostic composition of this study may explain differences from
previous work. Studies exploring the relationship between BDNF and
antidepressant response to ketamine have also yielded mixed findings
(Haile et al., 2014; Machado-Vieira et al., 2009). Other data-driven
approaches have considered both biological and behavioral variables in
characterizing depression (Drysdale et al., 2017); a similar approach
might prove useful for predicting SI response.
The present study is associated with several strengths as well as
limitations. Strengths include the relatively large sample size of participants
who received ketamine, the use of composite SI scores from
previous exploratory factor analyses as opposed to individual items,
and the combination of clinical and biological markers as potential
predictors of class membership. Limitations include patient selection
methods, as these patients were part of an antidepressant trial and were
not selected for active suicidal thoughts, as well as the exploratory
nature of the analysis. As stated above, suicidal thoughts do not necessarily
equate to suicidal behavior, and class membership would thus
not necessarily correspond with an overall reduction in suicide risk.
Another limitation is that results were collapsed across several clinical
trials with slight variations in study design, and findings were thus only
extended to Day 3 rather than a week after ketamine administration. As
a result, only a subset of the sample could be used for predictive analyses.
In addition, plasma—rather than CSF—markers were used, and
the latter might better indicate underlying biology due to proximity to
the brain, though certain markers such as plasma BDNF may be related
to platelet storage, rather than the brain (Chacón-Fernández et al.,
2016). Comparison of results to trajectories of suicide-specific measures,
such as the Scale for Suicide Ideation (Beck et al., 1979), may also
give further insight into specific SI content. Finally, many clinical
predictors were collected upon hospital admission; future analyses
could use formal assessments, such as the Childhood Traumatic Questionnaire
(Bernstein et al., 1994), assessment of personality disorders,
or diagnoses such as post-traumatic stress disorder (PTSD) as potential
indicators of response.
Despite these limitations, the study demonstrates the utility of a
data-driven approach for characterizing the heterogeneity of SI response
to a rapid-acting intervention. This allows for a more finegrained
analysis of symptoms than would be permitted by traditionalapproaches, such as overall average response or dichotomization at
50% reduction in symptoms. This study identified several findings of
note. These included distinguishing at least three patterns of SI response
to ketamine and finding that subjects who exhibited more severe SI at
baseline were not likely to experience an SI response to ketamine.

 

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Ketamine for resistant depression: Outstanding promise, outstanding issues.

Outstanding Promise.

Ketamine has been around for many years, firstly as a dissociative anaesthetic and then as a psychedelic drug. But it might become best known for it’s powerful antidepressant properties (Berman et al 2000Zarate et al 2006). Compared to existing antidepressants, which take around 2 weeks to work, ketamine exerts a large antidepressant effect on the first day of treatment.

depression ketamine murrough

Figure 1: The antidepressant effect of ketamine over 6 treatment sessions. The improvement on day 1 (measured using the MADRAS scale) was predictive of the response achieved following the sixth treatment session.

The robust antidepressant effect of ketamine also occurs in patients who have not found relief with existing drugs or with ECT. In the latest study to be reported, 24 patients with treatment-resistant depression underwent up to 6 sessions of intravenous ketamine (0.5mg/Kg in 40 mins) over ~2 weeks. Over 70% of patients responded to ketamine, and the overall reduction in depression was large and rapid (Murrough et al 2013) (Figure 1).

Outstanding Issues.

To date a major issue has been the lack of persistence of the antidepressant effect. In previous studies, involving a single ketamine treatment, depression returned within one week of the session or less. In the study by Murrough et al, this was extended to an average of 18 days. This is an improvement, but further work will be needed to solve the problem of the relatively short-lived antidepressant effect of ketamine.

An understanding of the mechanism by which ketamine alleviates depression may be necessary if we are to extend the duration of it’s beneficial effects. Pre-clinical work suggests that ketamine boosts the health and integrity of synapses and neuronal networks. Much of the action is believed to take place within dendritic spines, and involves local protein synthesis (Duman et al 2012) (Figure2).

ketamine mechanism
Ketamine | Ketamine virginia | Fairfax Ketamine | Ketamine infusions | 703-844-0184

Figure 2: The antidepressant effects of ketamine may depend upon activation of mTOR and local protein synthesis in dendritic spines.

Two molecules of relevance are mTOR and GSK-3. Ketamine enhances local protein synthesis by activating mTOR and by inhibiting GSK-3. [GSK-3 inhibits mTOR]. A drug, such as lithium, which inhibits GSK-3 might enhance the antidepressant effect of ketamine. This has now been demonstrated in pre-clinical studies (Liu et al 2013). The clinical question, which will now be addressed in trials is whether lithium treatment extends and enhances the antidepressant effects of ketamine. Lithium has been used for treatment-resistant depression for many years, and has a good evidence base (Bauer et al 2010) so that the combination of ketamine and lithium presents as an interesting and relatively straightforward strategy for stubborn depression.

However it is somewhat odd that the proposed mechanism for ketamine involves new protein synthesis and synaptogenesis (which take time, and are sustained) whereas the clinical effects of ketamine are very rapid (and transient). Other mechanisms may have more explanatory power. For instance a recent fMRI study showed that ketamine decreased the connectivity of limbic and prefrontal regions which are known to be overactive in depression (Scheidegger et al 2012). More provocatively, it appears that the antidepressant effect of ketamine depends upon the extent of the acute psychological reaction produced by the drug. Although the dissociative/psychedelic properties of ketamine are sometimes regarded as unwanted “side-effects”, a recent paper showed that the acute psychedelic and subsequent antidepressant effects are related (Sos et al 2013).

 2013;34(4):287-93.

Relationship of ketamine’s antidepressant and psychotomimetic effects in unipolar depression.

Abstract

OBJECTIVES:

Ketamine and other NMDA (N-methyl-D-aspartate) antagonists produce fast-acting antidepressant-like effects, although the underlying mechanism is unclear. Furthermore, high affinity NMDA antagonists such as ketamine are associated with psychotomimetic effects. To date the link between the antidepressant and psychotomimetic effects of ketamine has not been explored. We examined the relationship between the antidepressant and psychotomimetic effects of a single ketamine infusion in subjects diagnosed with major depressive disorder.

METHODS:

In a double-blind, cross-over, placebo-controlled, two weeks clinical trial we studied the effects of ketamine (0.54 mg/kg within 30 min) in a group of 27 hospitalized depressive patients.

RESULTS:

Higher intensity of psychotomimetic symptoms, measured using BPRS, during ketamine administration correlated with alleviation in mood ratings during the following week with maximum on day seven. Ketamine was superior to placebo in all visits (day 1, 4, and 7) assessed by MADRS with effect size (Cohen´s d) of 0.62, 0.57, and 0.44 respectively. There was no significant correlation between ketamine and nor-ketamine plasma levels and MADRS score change at any study time point.

CONCLUSION:

The substantial relationship between ketamine’s antidepressant and psychotomimetic effects was found. This relationship could be mediated by the initial steps of ketamine’s action, trough NMDA receptors, shared by both ketamine’s clinical effects.

GSK-3 Inhibition Potentiates the Synaptogenic and Antidepressant-Like Effects of Subthreshold Doses of Ketamine

Lithium’s Emerging Role in the Treatment of refractory major depression episodes – augmentation of antidepressants

Subanesthetic ketamine decreases the incentive-motivational value of reward-related cues.

The effects of subanesthetic ketamine infusions on motivation to quit and cue-induced craving in cocaine-dependent research volunteers.

Signaling Pathways Underlying the Rapid Antidepressant Actions of Ketamine

 

Cognitive disorders: the role of dendritic spines.

Cognitive disorders: the role of dendritic spines.

www.paulmorrison.org/cognitive-disorders-the-role-of-dendritic-spines/

Neuronal plasticity:

A major contribution of neuroscience to the humanities is the knowledge that the structure of the brain is moulded by the experiences the mind goes through – the phenomenon known as plasticity. It means that the circuits of the brain are sculpted by habitat, schooling, language, relationships, and culture, as well as by the unfolding genetic programme. The action occurs below the micrometre scale – at synapses (the points of connection between neurons) – and involves the exquisite choreography of a number of molecular machines. These molecular processes are so fundamental for cognition that their failure (whether driven by gene mutation or by harsh environments) results in neuropsychological disability. A major locus of plasticity (and hence, cognitive disability) is the dendritic spine.

pyramidal neuron

The dendrites of pyramidal neurons express thousands of dendritic spines. P=pyramidal neuron.

Principal neurons in the brain, such as cortical pyramidal neurons, express tens of thousands of small protruberances on their dendritic trees. These structures (dendritic spines) receive excitatory information from other neurons, and are highly dynamic. They can adjust their responsiveness to glutamate (the major excitatory neurotransmitter), becoming stronger (potentiation) or weaker (depression), as local circumstances dictate. This strengthening (LTP) or weakening (LTD) can be transient, or persist over long periods and as such, serves as an ideal substrate for learning and memory at synapses and in circuits. Potentiated spines increase in size, and express more AMPA glutamate receptors, whilst the opposite pattern occurs in synaptic depression to the extent that spines can be ‘absorbed’ back into the dendritic tree.

Over the course of childhood, dendritic spines (excitatory synapses) increase in number, but their numbers are ‘pruned’ back during adolescence to reach a plateau. Enriched environments have been shown to increase spine density, impoverished environments the opposite. In common psychiatric disorders, spine density is altered. For example, the most robust histological finding in schizophrenia is a reduction of spine density in the frontal cortex, auditory cortex and the hippocampus. In major depression, spines (and dendrites) are lost in the hippocampus. In autism, spine density actually increases. Finally, in Alzheimer’s and other dementias there is a catastrophic, and progressive loss of cortical and sub-cortical spines.

REGULATION OF THE SPINE:

The molecular biology of dendritic spines involves hundreds of proteins, but the outlines are now reasonably well understood. Scaffolding proteins [such as PSD95, shank(s), AKAP, stargazin and homer(s)] provide structural support and provide orientatation for membrane bound receptors, ion-channels and their downstream signalling pathways. The scaffold (post-synaptic density), facilitates effective signalling by ensuring that the correct protein partners are in close apposition. The scaffold is also tethered to proteins which bridge the synaptic cleft (cell adhesion molecules) and to bundles of actin filaments which provide the structure and force for spine enlargement (and retraction).

dendritic spine

Spine plasticity is fundamental for learning and memory. The shuttling of AMPA receptors underlies early phase plasticity. Modification of the actin cytoskeleton and local protein synthesis underlie long term plastic changes.

There is a constant remodelling of the actin cytoskeleton within the spine in response to synaptic and network signalling. Remodelling is via small, cytoplasmic G-proteins from the RHOfamily. Some family members promote the growth and stabilisation of actin filaments, whereas others promote actin disassembly. Mutations in the proteins which regulate actin dynamics are a cause of learning disability. Finally local protein synthesis (and degradation) occurs within dendritic spines, is tightly controlled and is essential for plasticity. Abnormalities in local protein synthesis within the spine underlie learning disability syndromes such as fragile X, neurofibromatosis and tuberous sclerosis.

Spine pathology:

Recent years have seen glutamate synapses move to centre stage in neuropsychiatry. This is not surprising given the role of pyramidal neurons (glutamate containing neurons) in information processing, and the role of glutamate transmission in learning and memory [see link]. But it is remarkable that so many psychological and cognitive disorders appear to ‘coalesce’ at dendritic spines.

The enclosed vector-graphic image [click here] highlights a selection of some of the proteins which are now known to be involved in autism, learning disability and schizoprenia.

Research will continue to decipher the complexity (and beauty) of the dendritic spine, but potential treatments are starting to emerge for disorders like fragile X, (which until recently were thought to be not amenable for drug treatment, as was the case for schizophrenia until the 1950s). Molecular neuroscientists will, almost certainly, continue to uncover more treatment targets. The task for psychiatry, as ever, is to keep abreast of neuroscience in all it’s complexity (and beauty).

Glutamate & GABA for psychiatrists

Rapid Dissemination of Information
Glutamate and GABA are the archetypal ‘fast’ transmitters. If a neuron in the brain ‘wishes’ to communicate rapidly with another cell, the chances are that it will utilise glutamate or GABA. Of course, glutamate neurons exert an excitatory influence on the cells they contact, whereas GABA, at least on first glance, is inhibitory.

Fast transmitters bind to receptors on membrane-spanning ion channels. An ion-channel is in constant flux between various conformations: e.g. open, closed, desensitised. Binding of fast transmitter ‘causes’ the ion channel to snap open for brief periods, and ions rush down their concentration gradients causing an abrupt, short-lived, change in the local membrane potential of the post-synaptic cell (Figure 1). From start to finish the whole process is over within tens of milliseconds, and constitutes a discrete electrical signal (termed an excitatory or inhibitory post-synaptic potential; EPSP, IPSP).

nmda receptor

Figure 1. The NMDA Receptor mediates an EPSP.

Neurotransmission v neuromodulation
Fast transmission, as a concept, pre-supposes slow transmission. The classical slow transmitters are the monoamines, e.g. noradrenaline and dopamine. These substances are used as transmitters by neurons within specific brainstem nuclei, whose axons project to numerous subcortical structures and large areas of cortex. There are relatively few monoamine neurons (tens of thousands), but their projections show massive arborisation within the ‘higher centres’ and the limbic system. Anatomically, glutamate and GABA signalling is characterised by point-to-point communication between narrowly separated (and tethered) pre-synaptic and post-synaptic elements, whereas for monoamine systems, the release sites (boutons) and post-synaptic receptors are not necessarily in close proximity. In contrast to glutamate and GABA, which convey a fast, discrete, short-lived electrical signal, monoamines evoke slower-onset, diffuse, longer-duration biochemical changes in their target neurons. Monoamine systems are not optimised for the rapid dissemination of specific information, but instead for modulating those neurons that are.

Ensemble formation and Gestalts
Pyramidal neurons (the principal output neuron of the hippocampus and cortex) use glutamate as a transmitter to communicate rapidly with neurons in ‘lower centres’ such as the striatum, thalamus, pontine nuclei and the cord although most communication is with other pyramidal neurons. Pyramidal neurons organise themselves into ensembles. This process, in which pyramidal neurons fire in synchrony for brief periods of time is thought to be essential for object perception and for movement, speech and thinking.

Consider a pyramidal neuron ‘sitting’ at resting-membrane-potential (-70mV). It receives tens of thousands of excitatory (glutamate) inputs on its dendritic spines, (dynamic structures that are moulded by experience over a lifetime). A single excitatory input (by itself) has little overall impact on the pyramidal neuron. But when numerous EPSP’s from a multitude of inputs arrive ‘synchronously’, the depolarisation may be sufficient for the pyramidal neuron to fire an action potential (AP). In short, the pyramidal neuron is recruited (by the ensemble) into joining the ensemble.

It can be grasped that for AP firing to occur in a pyramidal neuron, there has to be a convergence of excitatory information from numerous sources. Excitatory inputs come from various thalamic nuclei and from stellate cells (in primary sensory cortices), although the overwhelming majority come from other pyramidal neurons. Regardless of the source, timing is key. In order to generate enough depolarisation to trigger an AP, inputs must arrive (and summate) within the same narrow time window (of the order of milliseconds).

Precise Timing and cortical dynamics
The output of a pyramidal neuron (AP spiking) is finely controlled. Precise timing is so fundamental for cortical processing that various auxiliary neurons appear to be tasked with a pacemaker role. These neurons utilise GABA as a transmitter. Classical neuroscience conceptualised GABA containing neurons as nothing more than inhibitory interneurons – this is no longer tenable. There are various populations of GABA containing neuron, which have been classified according to their morphology, their location in the cortex, which proteins they use to sequester calcium, and their electrophysiological properties. Some are even excitatory. For simplicity, we shall restrict ourselves to a simple classification based upon where the GABA neuron contacts the pyramidal neuron (Figure 2).

glutamate and gaba neurons

Figure 2. A pyramidal neuron receives inhibitory GABA-ergic input to its dendrites. GABA pacemakers synapse on the soma and axon initial segment.

 

Contacts formed with the dendrites of pyramidal neurons function as inhibitory interneurons in the classical sense (i.e. they oppose excitatory drive), whereas GABA neurons targeting the soma or the proximal axon (of the pyramidal neuron) function as pacemakers. We can consider how these GABA pacemaker neurons are optimised for their task. Firstly they have very fast dynamics, swifter for example than the pyramidal neurons that they make contact with. Secondly, they provide a very strong and reliable signal to the pyramidal neuron by engulfing the soma or the proximal axon with numerous terminals. A strong, brief, recurrent signal to the soma and proximal axon creates a series of time windows, which determine precisely when the pyramidal neuron fires. Thirdly, individual pacemaker neurons make contact with numerous local pyramidal neurons. And finally, groups of pacemaker neurons are connected by electrical synapses (gap junctions) so that they can function as an interconnected single entity, a syncytium. For completion, pyramidal neurons make strong, reliable synapses (excitatory) with pacemaker neurons.

It is readily apparent that the interconnectivity of pyramidal neurons and GABA interneurons favours the emergence of oscillations, with successive, precisely timed periods of integration followed by periods of AP discharge. Experiments have shown that the population of neurons in an active ensemble generate the rhythm, whilst the rhythm puts precise constraints upon when an individual neuron can fire.

Systems and levels
For slow, diffuse modulators such as noradrenaline, it makes sense to talk of a system. To recap, noradrenaline [NA] is synthesized by no more than tens of thousands of neurons, confined to discrete nuclei within the brainstem, and is ‘sprayed’ from en-passant boutons over large territories of CNS tissue, in a hormone-like manner. Crucially, the release patterns of noradrenaline [and other neuromodulators] can be clearly mapped onto distinct behavioural states, the most marked differences arising in the sleep-state [noradrenaline – ‘off’] versus the waking-state [noradrenaline – ‘on’]. Since the extracellular concentrations of noradrenaline [and other neuromodulators] can inform directly about higher brain/mind levels, the idea of a noradrenergic system has utility.

Glutamate and GABA are too ubiquitous as fast point-to-point transmitters for the term ‘system’ to be applicable in the same way. Particular patterns of behaviour cannot be mapped onto the release of GABA or glutamate at a specific locus. All we can say is that neurons in an ensemble use glutamate and GABA to communicate with each other. Whereas transient fluctuations in the extracellular concentrations of GABA/glutamate do not reveal anything about behaviour, the dynamics of neuronal ensembles correspond with distinct behavioural states. Again the sleep wake-cycle is illustrative. Oscillatory activity generated by the ensemble can be mapped unambiguously onto the sleep-state and the waking-state.

Learning & Memory
In the 1970s it became clear that excitatory connections onto pyramidal neurons could be made stronger, if they were subjected to particular patterns of input. This was the first experimental support for an idea that can be traced back to Ramon y Cajal – the idea that synapses are modifiable (plastic) and that such plasticity might serve as the physical basis of memory.

There are various forms of plasticity, but the most widely studied is NMDA-dependent long-term potentiation (LTP). In the early 1980’s, researchers based in Bristol showed that NMDA receptor antagonists could block the initiation of LTP [and subsequent behavioural experiments, (most famously, by Richard Morris in Edinburgh) showed that such drugs could inhibit new learning].

NMDA receptor channels are found at the heads of dendritic spines, adjacent to the glutamate terminal. AMPA receptor channels are found in the same locale. When activated, both receptor channels produce an excitatory-post-synaptic-potential (EPSP). In the case of the AMPA receptor, the EPSP is mediated by sodium ions flowing into the spine. For NMDA receptors, the EPSP is mediated by a combination of sodium and calcium ions. [It is the calcium signal that initiates LTP (Figure 3). Early-phase LTP is mediated by phosphorylation of AMPA receptors (increasing their conductance) and by insertion of new AMPA receptors into the post-synaptic membrane].

long term potentiation

Long Term Potentiation (LTP) is induced by NMDA receptor activation. The mechanism of early-phase LTP involves the enhancement of AMPA receptor conductances and insertion of new AMPA receptors into the post-synaptic membrane.

AMPA and NMDA receptor channels differ in one other key property. The NMDA channel is voltage-dependent. At membrane potentials less than -50mV, the NMDA channel remains closed, even if glutamate is bound to the receptor. For the NMDA channel to snap open, the membrane potential must be already depolarised to at least -30mV. So two conditions are necessary for NMDA conductance; binding of glutamate and membrane depolarisation. For this reason, the NMDA receptor is said to be a coincidence detector (or in engineering terms, an AND gate).

Sufficient post-synaptic depolarisation can occur from backward-propagating action potentials (APs) or from temporally or spatially summated excitatory input to a dendritic branch. Research in the last decade has revealed that the timing of pre-synaptic activity (glutamate release) and of post-synaptic activity (post-synaptic-depolarisation) is critical in determining whether synaptic strength will be altered. Pre and post synaptic ‘events’ must occur within approximately 20 milliseconds, otherwise synaptic strength remains unchanged. This form of plasticity, known as Spike-Timing-Dependent-Plasticity (SDTP), is likely to become increasingly relevant as we begin to conceptualise ‘micro-circuit’ abnormalities in major neurodevelopmental disorders. Two final points about SDTP will be made here. Plasticity is bidirectional (potentiation or depression) depending on the order of pre and post-synaptic events. And conventional modulators such as dopamine can impact upon the timing rules and alter the direction of the plasticity, (LTP or LTD).

Some Psychiatry: The K-Hole and beyond
Ketamine, a drug that has attracted the attention of psychiatrists in the past few decades, ‘blocks’ the NMDA channel. It has been used as a model psychosis, and latterly has been demonstrated to have acute anti-depressant properties. (It certainly impairs new learning, as would be expected).

Downstream of NMDA blockade, there is no clear consensus as to how ketamine produces a psychosis. Counter-intuitively (for a glutamate antagonist), ketamine increases the excitability (spiking) of pyramidal neurons. Ketamine also increases the power of gamma band (~40 Hz oscillations) and some have proposed that ‘kernels’ of ‘abnormal’ gamma underlie the psychotic-like effect.

But the behavioural pharmacology of ketamine is far from straightforward. Rating-scales used in schizophrenia research, are probably not ideal for capturing the nuances of the drug. Those who have taken a more phenomenological approach [in the sense of ‘bracketing-out’ existing assumptions, whilst focussing on clear descriptions] have identified a much richer and more complex behavioural psychopharmacology, which includes euphoria, near-death experiences, the cessation of time, the dissolution of the ego, and the experience of being immersed in fractal geometries or boundless oneness (Jansen K, Ketamine: Dreams & Realities 2000).

Close observation reveals the dose-dependent emergence of an oneroid (dream-like) state, and other catatonic features (ambitendency, posturing) but not a classic paranoid psychosis. Researchers have also tended to assume that ketamine can ‘cause’ negative symptoms, but reports of euphoria, terror and awe are inconsistent with this categorisation. Motor output (which includes speech of course) is certainly restricted following ketamine, but because the concurrent inner world is a kaleidoscope of strange, mystical and fantastic experiences with extremes of emotion, the overall picture is far removed from the negative syndrome.

Nevertheless, ketamine is frequently championed as the most convincing drug-model of schizophrenia because it can induce negative symptoms, on a rating scale. The irony perhaps is that the ketamine experience might actually be more schizophrenia-like than many of its proponents have suggested. Ketamine elicits phenomena, which are now very rarely encountered in psychiatric clinics, given the modern-day domination of the softer, paranoid form of the illness.

Update

Paul Janssen’s genius was in predicting that a drug which blocked the effects of amphetamine in animals, would be an effective treatment for those cases of schizophrenia that resembled an amphetamine psychosis (characterised by agitation, hallucinations and delusions)[link]. That drug was haloperidol, and that class of drug (D2 dopamine receptor antagonists) changed the landscape of psychiatry.

Janssen’s logic would also suggest that a drug which inhibited the effects of ketamine in animals, would be an effective treatment for those cases of schizophrenia which resemble ketamine-elicited psychopathology (characterised by bizarre, inaccessible dream-like states, and psychotic motor phenomena. i.e. cases where ECT becomes a sensible option). A pharmacological antagonist of ketamine (in animals) proved to be ineffective against human paranoid schizophrenia. Perhaps this could have been predicted, by closer attention to the phenomenology of ketamine. The question now is whether ‘The Lilly compound‘ has efficacy against non-paranoid schizophrenia?

Natural antidepressants & new brain cells

New Brain Cells

In the last decade it has become clear that new cells can form in the adult brain. This happens in a region known as the hippocampal complex. The hippocampal complex is found deep inside either temple and is crucial for memory and emotion. The hippocampal complex inhibits the human stress response, but can itself be damaged by persistent stress, leading to a vicious cycle in which the stress response is amplified further and depression ensues.

hippocampus from nieuwenhuys et al

The hippocampal complex is found in the temporal lobe, and has a crucial role in regulating the stress response.

Experimental work suggests that neurogenesis (the birth of new neurons) in the hippocampal complex is vital for the action of conventional antidepressant drugs. Exercise and enriched environments also promote neurogenesis, whilst stress has the opposite effect.The current picture is that hippocampal health (including the birth of new neurons) is essential for protecting the organism against the effects of stress, so that if hippocampal functioning is compromised, anxiety and depression can emerge.

 

Natural Antidepressants

There has been recent interest in the antidepressant properties of a natural molecule called curcumin. This substance is found in the herb turmeric. As well as a foodstuff, turmeric has been used for centuries in traditional Indian medicine (Ayurveda). In pre-clinical studies, curcumin exhibited clear antidepressant effects.

curcumin

Research has focused on the mechanism of action of curcumin. Remarkably it appears that curcumin can also increase the birth of new neurons in the hippocampal complex. This is an intriguing finding which hints at the possibility of a new class of antidepressant drug.

A new paper from researchers at King’s College London provides an excellent summary of work in this area. The full paper can be read here.