Lower 3H-paroxetine binding in cerebral cortex of suicide victims is partly due to fewer high affinity, non-transporter sites

Is there a relationship between morphological and functional platelet changes and depressive disorder?

BACKGROUND

Blood platelets, due to shared biochemical and functional properties with presynaptic serotonergic neurons, constituted, over the years, an attractive peripheral biomarker of neuronal activity. Therefore, the literature strongly focused on the investigation of eventual structural and functional platelet abnormalities in neuropsychiatric disorders, particularly in depressive disorder. Given their impact in biological psychiatry, the goal of the present paper was to review and critically analyze studies exploring platelet activity, functionality, and morpho-structure in subjects with depressive disorder.

METHODS

According to the PRISMA guidelines, we performed a systematic review through the PubMed database up to March 2020 with the search terms: (1) platelets in depression [Title/Abstract]"; (2) "(platelets[Title]) AND depressive disorder[Title/Abstract]"; (3) "(Platelet[Title]) AND major depressive disorder[Title]"; (4) (platelets[Title]) AND depressed[Title]"; (5) (platelets[Title]) AND depressive episode[Title]"; (6) (platelets[Title]) AND major depression[Title]"; (7) platelet activation in depression[All fields]"; and (8) platelet reactivity in depression[All fields]."

RESULTS

After a detailed screening analysis and the application of specific selection criteria, we included in our review a total of 106 for qualitative synthesis. The studies were classified into various subparagraphs according to platelet characteristics analyzed: serotonergic system (5-HT2A receptors, SERT activity, and 5-HT content), adrenergic system, MAO activity, biomarkers of activation, responsivity, morphological changes, and other molecular pathways.

CONCLUSIONS

Despite the large amount of the literature examined, nonunivocal and, occasionally, conflicting results emerged. However, the findings on structural and metabolic alterations, modifications in the expression of specific proteins, changes in the aggregability, or in the responsivity to different pro-activating stimuli, may be suggestive of potential platelet dysfunctions in depressed subjects, which would result in a kind of hyperreactive state. This condition could potentially lead to an increased cardiovascular risk. In line with this hypothesis, we speculated that antidepressant treatments would seem to reduce this hyperreactivity while representing a potential tool for reducing cardiovascular risk in depressed patients and, maybe, in other neuropsychiatric conditions. However, the problem of the specificity of platelet biomarkers is still at issue and would deserve to be deepened in future studies.

SLC6A3 (DAT1) as a Novel Candidate Biomarker Gene for Suicidal Behavior

It has been previously shown that the serotonin and dopamine neurotransmitter systems might influence the predisposition to suicidal behavior. This study aims to estimate the contribution of 11 polymorphisms in the genes SLC6A4 (5HTT), HTR1A, HTR2A, HTR1B, SLC6A3 (DAT1), DRD4, DRD2, COMT, and BDNF to suicidal behavior and severity of symptoms of depression and anxiety in the Russian population. The study was performed on 100 patients with repeated suicide attempts and 154 controls. We first found an association between SLC6A3 (DAT1) 40 bp VNTR locus and suicidal behavior. This association was significant; when using the codominant (p = 0.006), dominant (p = 0.001), overdominant (p = 0.004), and log-additive (p = 0.004) models, LL genotype played a protective role (OR = 0.48, 0.29–0.82, p = 0.005). Difference in the distribution of COMT rs4680 genotypes was significant in the codominant (p = 0.04), dominant (p = 0.013), and log-additive (p = 0.02) models, and AA genotype might protect against suicide (OR = 0.49, 0.26–0.91, p = 0.025). SLC6A4 5-HTTLPR + rs25531 locus was significant in the recessive model (p = 0.024), and also affected the severity of symptoms of depression (p = 0.044) and personal anxiety (p = 0.029). Our results suggest that allelic variants of SLC6A3, COMT, and SLC6A4 genes might be considered as risk factors for suicidal attempts.

Sunshine, temperature and suicidal behaviour in patients treated with antidepressants: an explorative nested case-control study

Our aim was to explore if different exposure windows for sunshine or temperature are associated with increased suicidal behaviour among people starting antidepressant treatment. 307 completed and 1674 attempted suicides were included as cases in the conditional logistic regression analyses, while controlling for potential confounders, including season, as well as temperature and hours of sunshine when these variables were not the main exposure variable. Ten controls were matched to each case using risk-set sampling. The role of season, age, and sex was examined with likelihood ratio tests (LRTs) with and without the respective interaction terms and with stratified analyses. There was no overall association between temperature or sunshine with suicidal behaviour. Age was a significant effect modifier for suicide and suicide attempt for both sunshine and temperature exposure. In stratified analyses, an increase of one degree Celsius in the average daily temperature during the last 4 weeks was associated, in the unadjusted model, with a 3% increase in the rate of suicide (p = 0.023) amongst older patients (65+). In the same age group, an increase of 1 h in the average daily sunshine during the last 4 weeks was associated with an 8% increase in the rate of suicide attempt (p = 0.002), while the respective increase for the exposure period of 5–8 weeks was 7% (p = 0.007). An increase of one degree Celsius in the average daily temperature during the last 4 weeks was associated with a 3% increase in the rate of suicide attempt (p = 0.007). These associations did not retain statistical significance in the adjusted models. No associations were found in the other age groups. Our results point to a possible effect modification by age, with higher risk of suicidal behavior associated with an increase in sunshine and temperature found in the older age groups.

Season of treatment initiation with antidepressants and suicidal behavior: A population-based cohort study in Sweden

BACKGROUND

Decreased binding capacity of SERT in the prefrontal cortex has been observed in both suicide victims and suicide attempters. Moreover, some studies have shown that SERT has a seasonal variation with lower binding capacity in the spring and summer, which coincides with a seasonal peak of suicides. Our aim was to explore whether the season of treatment initiation with antidepressants is associated with suicide or suicide attempt and compare it with the underlying suicide seasonality in the general population.

METHODS

Using Swedish registers, patients who initiated treatment with an antidepressant were followed up to three months for suicidal behavior. Cox regression analyses were used. Results were compared with the underlying seasonal pattern by calculating standardized mortality ratios (SMRs) for suicides and standardized incidence ratios (SIRs) for suicide attempts.

RESULTS

Patients aged ≥65 years had higher risk for suicide when initiating antidepressant treatment in the summer, and also a higher risk for suicide attempt when initiating treatment in the spring and summer. Young patients (0-24 years) presented a higher risk for suicide attempt when initiating treatment in the autumn. Patients with previous suicide attempt had a seasonal pattern, with a higher risk to carry out a suicide attempt in the summer and autumn. Results from the SMR and SIR calculations numerically support these findings.

LIMITATIONS

We used information of filling an antidepressant prescription as a proxy of actual antidepressant treatment. Patients with combination, augmentation therapy or those switching antidepressant during follow-up were excluded. Thus, our results refer to less complicated psychopathology.

CONCLUSIONS

Our results indicate an interaction between biological and health care-related factors for the observed seasonal pattern of suicidal behavior in the elderly, whereas psychological and societal factors may be more important for the seasonality observed in the younger patients.

Suicide: scientific overview and relevance for trauma care providers

The World Health Organization estimates that in the year 2000, approximately one million people died from suicide worldwide. Over the last 45 years, suicide rates have increased by 60%, with a particularly precipitous rise among young people. The underlying psychology of suicide is complex and individual. However, certain themes emerge from studying individuals who have attempted or completed suicides. This paper will provide an overview of suicide and suicidal behaviour as it relates to trauma practitioners, detailing risk factors, biologic and genetic interactions, and opportunities for prevention and treatment.

No association between the HTR1A gene and suicidal behavior: a meta-analysis

OBJECTIVE

Dysfunction of serotonin 1A receptors (HTR1A) may play a role in the genesis of suicidal behavior. We studied the association between a functional polymorphism in the HTR1A gene and suicidal behavior.

METHOD

We performed a meta-analysis of published genetic association studies by searching through Medline, PubMed, and Web of Science databases to analyze a possible correlation between the rs6295 polymorphism and suicidal behavior in different populations.

RESULTS

Four studies comprising a total of nine hundred and fifty seven patients with suicidal behavior and nine hundred and fifty seven controls were the eligible. The G allele of the rs6295 polymorphism may not be associated with suicidal behavior (Random-effects model: OR = 1.08; 95% CI: 0.80-1.45; p(Z) = 0.80) in presence of heterogeneity (Q = 17.84, df = 4, p = 0.0013). In a second analysis that presented no heterogeneity, a negative association was also observed (OR = 0.94; 95%CI: 0.79-1.13; p(Z) = 0.99).

CONCLUSION

To our knowledge, the present study is the first meta-analysis searching for a correlation between rs6295 of HTR1A and suicidal behavior. Our results showed no association between HTR1A and suicidal behavior. However, more studies assessing different populations, as well as larger samples, are needed.

Depression and thoughts of death among disadvantaged mothers: risk factors and impact on maternal and child health

Our hypothesess were that modifiable societal risk factors would contribute to depression and thoughts of death (DTD) and that DTD would affect maternal and infant well-being. Retrospective database analysis with bivariate and multivariate statistics utilizing 3 years of data from the prospective Fragile Families and Child Wellbeing Study. Eight hundred and eighty mothers (18%) were clinically depressed; of these, 286 (33%) reported thoughts of death. DTD were significantly associated with family violence and alcohol use; a combination of DTD with family violence or maternal alcohol use markedly increased the risk of infant hospitalization (p-value < 0.001). The association of DTD with problems of violence, substance abuse, and health outcomes underscores the complex relationships among these risk factors. Routine screening for these issues should be implemented.

Suicide neurobiology

In this review, we examine the history of the neurobiology of suicide, as well as the genetics, molecular and neurochemical findings in suicide research. Our analysis begins with a summary of family, twin, and adoption studies, which provide support for the investigation of genetic variation in suicide risk. This leads to an overview of neurochemical findings restricted to neurotransmitters and their receptors, including recent findings in whole genome gene expression studies. Next, we look at recent studies investigating lipid metabolism, cell signalling with a particular emphasis on growth factors, stress systems with a focus on the role of polyamines, and finally, glial cell pathology in suicide. We conclude with a description of new ideas to study the neurobiology of suicide, including subject-specific analysis, protein modification assessment, neuroarchitecture studies, and study design strategies to investigate the complex suicide phenotype.

TPH2 -703G/T SNP may have important effect on susceptibility to suicidal behavior in major depression

BACKGROUND

Serotonergic system-related genes can be good candidate genes for both major depressive disorder (MDD) and suicidal behavior. In this study, we aimed to investigate the association of serotonin 2A receptor gene -1438A/G SNP (HTR2A -1438A/G), tryptophan hydroxylase 2 gene -703G/T SNP (TPH2 -703G/T) and serotonin 1A receptor C-1019G (HTR1A C-1019G) with suicidal behavior.

METHODS

One hundred and eighty one suicidal depressed patients and 143 non-suicidal depressed patients who met DSM-IV criteria for major depressive disorder were recruited from patients who were admitted to Korea University Ansan Hospital. One hundred seventy six normal controls were healthy volunteers who were recruited by local advertisement. Patients and normal controls were genotyped for HTR2A -1438A/G, TPH2 -703G/T and 5-HT1A C-1019G. The suicidal depressed patients were evaluated by the lethality of individual suicide attempts using Weisman and Worden's risk-rescue rating (RRR) and the Lethality Suicide Attempt Rating Scale-updated (LSARS-II). In order to assess the severity of depressive symptoms of patients, Hamilton's Depression Rating Scale (HDRS) was administered. Genotype and allele frequencies were compared between groups by chi(2) statistics. Association of genotype of the candidate genes with the lethality of suicidal behavior was examined with ANOVA by comparing the mean scores of LSARS and RRR according to the genotype.

RESULTS

There were statistically significant differences in the genotype distributions and allele frequencies of TPH2 -703G/T between the suicidal depressive group and the normal control group. The homozygous allele G (G/G genotype) frequency was significantly higher in suicidal depressed patients than in controls. However, no differences in either genotype distribution or in allele frequencies of HTR2A -1438A/G and HTR1A C-1019G were observed between the suicidal depressed patients, the non-suicidal depressed patients, and the normal controls. There were no differences in the lethality of suicidal behavior in suicidal depressed patients according to the genotypes of three polymorphisms.

CONCLUSION

Our results suggest that TPH2 -703G/T SNP may have an important effect on susceptibility to suicidal behavior. Furthermore, an increased frequency of G allele of TPH2 SNP may be associated with elevated suicidal behavior itself rather than with the diagnosis of major depression and may increase risk of suicidality, independent of diagnosis.

Altered expression of genes involved in ATP biosynthesis and GABAergic neurotransmission in the ventral prefrontal cortex of suicides with and without major depression

The prefrontal cortex is believed to play a major role in depression and suicidal behavior through regulation of cognition, memory, recognition of emotion, and anxiety-like states, with numerous post-mortem studies documenting a prefrontal serotonergic dysregulation considered to be characteristic of depressive psychopathology. This study was carried out to detect changes in gene expression associated with both suicide and major depression using oligonucleotide microarrays (Affymetrix HG-U133 chip set) summarizing expression patterns in primarily ventral regions of the prefrontal cortex (BA44, 45, 46 and 47). A total of 37 male subjects were included in this study, of which 24 were suicides (depressed suicides=16, nondepressed suicides=8) and 13 were matched controls. All subjects were clinically characterized by means of psychological autopsies using structured interviews. Unique patterns of differential expression were validated in each of the cortical regions evaluated, with group-specific changes highlighting the involvement of several key neurobiological pathways that have been implicated in both suicide and depression. An overrepresentation of factors involved in cell cycle control and cell division (BA44), transcription (BA44 and 47) and myelination (BA46) was seen in gene ontology analysis of differentially expressed genes, which also highlights changes in the expression of genes involved in ATP biosynthesis and utilization across all areas. Gene misexpression in BA46 was most pronounced between the two suicide groups, with many significant genes involved in GABAergic neurotransmission. The pronounced misexpression of genes central to GABAergic signaling and astrocyte/oligodendrocyte function provides further support for a central glial pathology in depression and suicidal behavior.

Differences in cytokines between non-suicidal patients and suicidal patients in major depression

Several studies have shown that there is an imbalance between pro-inflammatory and anti-inflammatory cytokines in major depressive disorder (MDD). However, little is known about the role of cytokines in suicide. In the present study, amounts of IL-6, IL-2, IFN-gamma, IL-4, and TGF-beta1 produced by mitogen-stimulated whole blood were measured in 36 MDD patients who had recently attempted suicide, 33 non-suicidal MDD patients, and 40 normal controls. The severity of depression symptoms and suicidal behaviors was evaluated using Hamilton's depression rating scale (HDRS), the Lethality Suicide Attempt Rating Scale (LSARS), and the Risk-Rescue Rating (RRR). Non-suicidal MDD patients had significantly higher IL-6 production than suicidal MDD patients and normal controls (p<0.001). Suicidal MDD patients had significantly lower IL-2 compared with non-suicidal patients and normal controls (p<0.001). Both MDD groups, with or without attempted suicide, had significantly lower IFN-gamma and IL-4 and higher TGF-beta1 production. HDRS scores had significant positive correlations with IL-6, IFN-gamma, and the Th1/Th2 ratio and significant negative correlations with IL-4 in non-suicidal depression patients (p<0.005); however, these correlations did not hold true for suicidal patients. Suicidal MDD patients had no significant correlations between the LSARS or RRR scores and cytokine release. Our findings suggest that the immune response has distinct differences between non-suicidal patients and suicidal patients. Non-suicidal MDD may be associated with increased IL-6 production and a Th1/Th2 imbalance with a shift to Th1, while suicidal MDD may be associated with decreased IL-2.

Platelet serotonin concentration and suicidal behavior in combat related posttraumatic stress disorder

Posttraumatic stress disorder (PTSD) is a serious and global problem, a psychiatric disorder that frequently occurs with different comorbidities, and is associated with a high suicide rate. Pathophysiologically, both PTSD and suicidal behavior are related to disturbances in the central serotonergic system. Serotonin (5-hydroxytryptamine, 5-HT) controls emotional behavior, anxiety, impulsivity and aggression, and nearly all known antidepressants and antianxiety drugs affect 5-HT transmission. Platelet 5-HT can be used as a limited peripheral marker of the central serotonergic synaptosomes, since it is related to particular basic psychopathological characteristics of several psychiatric disorders. Platelet 5-HT concentration has been reported to be similar in PTSD subjects and healthy controls, but suicidal patients across different psychiatric diagnoses have reduced platelet 5-HT concentration. This study examined platelet 5-HT concentration by the spectrofluorimetric method in male subjects: 73 suicidal and 47 non-suicidal veterans with current and chronic combat related PTSD, 45 suicidal and 30 non-suicidal comparative non-PTSD subjects and 147 healthy men. The presence of suicidal behavior (score=0, non-suicidal; scores > or =1, suicidal) was assessed with the Hamilton Depression Rating Scale-17 (HDRS). Platelet 5-HT concentration was significantly lower in suicidal PTSD and non-PTSD patients compared to non-suicidal patients or healthy controls. Since the majority of patients scored very low on item 3 of HDRS, no significant correlation between suicidal scores and platelet 5-HT concentration was found. These results show that reduced platelet 5-HT concentration is related to suicidal behavior in PTSD, and suggest that platelet 5-HT concentration might be used as a peripheral marker to predict suicidal behavior across psychiatric diagnoses.

Positron emission tomography study of regional brain metabolic responses to a serotonergic challenge in major depressive disorder with and without comorbid lifetime alcohol dependence

This is the first study contrasting regional glucose metabolic rate (rCMRglu) responses to a serotonergic challenge in major depressive disorder (MDD) with and without comorbid alcohol dependence. In a university hospital, patients with MDD without a history of alcohol dependence (MDD only) and patients with MDD and comorbid alcohol dependence (MDD/ALC) were enrolled in this study. Subjects with comorbid borderline personality disorder were excluded. A bolus injection of approximately 5 mCi of (18)fluorodeoxyglucose was administered 3 h after the administration of placebo or fenfluramine. We found an anterior medial prefrontal cortical area where MDD/ALC subjects had more severe hypofrontality than MDD only patients. This area encompassed the left medial frontal and left and right anterior cingulate gyri. This group difference disappeared after fenfluramine administration. The fact that the observed group difference disappeared after the fenfluramine challenge suggests that serotonergic mechanisms play a role in the observed differences between the groups.

A prospective study of the association of cerebrospinal fluid monoamine metabolite levels with lethality of suicide attempts in patients with bipolar disorder

OBJECTIVES

Bipolar disorder is a severe illness that is associated with suicidal behavior. A biological predictor of highly lethal suicide attempts in patients with bipolar disorder would be valuable. We hypothesized that cerebrospinal fluid (CSF) monoamine metabolite levels are related to lethality of suicide attempts in bipolar patients and examined the relation between CSF 5-hydroxyindolacetic acid (5-HIAA), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG) levels and maximum lethality of suicide attempts at baseline and during a 2-year follow up.

METHODS

Twenty-seven bipolar depressed patients participated in the study. Demographic and clinical parameters were examined and recorded. Lumbar punctures were performed and CSF 5-HIAA, HVA, and MHPG were assayed by high-performance liquid chromatography with electrochemical detection. Following discharge, patients were evaluated after 3 months, 1 year, and 2 years. Each follow-up interview included an in-depth assessment of suicidal behavior during the intervening time period.

RESULTS

Six subjects made suicide attempts during the 2-year follow-up. Bipolar patients who attempted suicide during the follow-up period had higher aggression and hostility scale scores compared to bipolar subjects who did not make a suicide attempt during the follow-up period. CSF 5-HIAA, HVA, and MHPG levels were negatively correlated with the maximum lethality of suicide attempts during the 2-year follow-up period.

CONCLUSIONS

Our finding is the first observation that CSF monoamine metabolite levels may be predictors of lethality of suicide attempts in patients with bipolar disorder. Further studies are necessary to answer the question whether CSF monoamine metabolite levels are clinically useful biochemical predictors of highly lethal suicide attempts or completed suicides.

Serotonergic and Noradrenergic Neurobiology of Alcoholic Suicide

BACKGROUND

Alcoholism is associated with alterations in the serotonergic and noradrenergic systems. Alcoholics are at a significantly higher risk for suicide than the general population. Altered serotonin (5-HT) function is associated with suicide and serious suicide attempts. We hypothesized patterns of abnormality associated independently with suicide and with alcoholism.

METHODS

Quantitative autoradiographic experiments were performed in human postmortem brain tissue sections from alcoholics, alcoholic-suicide decedents, nonalcoholic suicide decedents, and normal controls diagnosed by psychological autopsy.

RESULTS

Binding to 5-HT1A receptors is lower in both alcoholic suicides and alcoholic nonsuicides, suggesting that this effect is related to alcoholism and not suicide. In nonalcoholic suicides, there is a localized increase in 5-HT1A binding in ventral prefrontal cortex, hypothesized to be a response to less serotonin input. Therefore, alcoholic suicides may fail to up-regulate ventral prefrontal 5-HT1A receptors in response to decreased serotonergic transmission, failing to mitigate the impact of less serotonin upon signal transduction and thereby increasing the risk of suicidal behavior. Binding to the serotonin transporter is low in alcoholic suicides but not in alcoholic nonsuicides, suggesting an association with suicide, as nonalcoholic suicides also have decreased binding compared with controls. Evidence of impaired serotonergic innervation associated with alcoholism is also manifested by less 5-HT1D terminal autoreceptor binding in alcoholics. Nonalcoholic suicides do not have lower 5-HT1D binding. In the noradrenergic system, alcoholics (suicide and nonsuicide) and nonalcoholic suicide victims all have fewer pigmented locus ceruleus neurons compared with controls, yet beta1-adrenergic binding is low in both alcoholic groups, whereas alpha1-and alpha2-adrenergic binding decreases are more pronounced in the alcoholic suicide group. These noradrenergic findings differ from those in nonalcoholic suicides, which have a common feature with alcoholics in having less alpha2-and beta1-adrenergic binding but more alpha1-adrenergic binding in ventrolateral and orbital cortex.

CONCLUSION

Extensive but different abnormalities in both the serotonergic and noradrenergic systems have been identified in alcoholics and suicides, suggesting two separate patterns: one related to alcoholism and the other related to suicide. The different patterns suggest different causes and homeostatic responses for alcoholism and suicide.

Genetics of suicide

The concept that genetic factors contribute to the complex trait of suicidal behaviour has stimulated much work aimed at identifying susceptibility genes. So far molecular genetic studies focused on the serotonergic pathway as the intent to die and the lethality of suicide acts were related to the serotonergic system. Two genes have so far emerged as being involved in the vulnerability for suicidality: first, the intronic polymorphisms (A218C or A779C) of the tryptophan hydroxylase 1 (TPH1) gene, which was suggested as a quantitative risk factor for suicidal behaviour; second, the insertion/deletion polymorphism of the serotonin transporter gene (5-HTTLPR), which does not seem to be involved in general suicidal behaviour, but in violent and repeated suicide attempts. The data have further shown that the MAOA gene, which is consistently associated with impulsive-aggressive personality traits, is not related to suicide but might induce violent methods in subjects with other suicide risk factors. Predominantly negative were the findings with any type of the serotonin receptors and inconsistent with catecholamine-synthesizing and -metabolizing enzymes or with the dopaminergic receptors. This paper reviews the status of current knowledge in this area, points to the weakness of the investigations and presents new approaches beyond the serotonergic system.

Postmortem serotonin (5-HT) concentrations in the cerebrospinal fluid of medicolegal cases

In a medicolegal study the postmortem serotonin (5-HT) cerebrospinal fluid (CSF) concentrations were determined in routine autopsies using a high performance liquid chromatographic procedure with electrochemical detection. There was no correlation between 5-HT concentrations and age, sex or blood alcohol concentration using a postmortem delay < or = 3 days. In suicides the suboccipital CSF concentrations were significantly decreased compared to the levels measured in the control group (8.55+/-5.99 ng/ml versus 20.15+/-13.56 ng/ml). Additionally, a decrease of 5-HT was found in the suboccipital CSF of opiate fatalities (15.56+/-13.52 ng/ml). The results support the hypothesis that decreased 5-HT concentrations in the CSF are characteristic in suicides. However, due to a rather broad overlapping of values between suicides and controls the results failed to define a possible cut-off level in the 5-HT CSF concentration to distinguish between a suicidal and a non-suicidal incident.

Serotonin transporter: a potential substrate in the biology of suicide

Suicide is a serious public health problem in the US, yet its neurobiological underpinnings are poorly understood. Suicide is highly correlated with depressive symptoms, and considerable evidence suggests that depression is associated with a relative deficiency in serotonergic neurotransmission. Serotonergic circuits also mediate impulsivity, a trait obviously relevant to suicide. These findings, taken together, suggest that alterations in the serotonergic system might contribute to suicidal behavior, serving as an impetus for researchers to scrutinize the serotonin transporter (SERT) as a potential substrate for the pathophysiology of suicide. Using post-mortem brain tissue, platelets, and DNA from suicide completers and attempters have not provided unequivocal evidence for a pre-eminent role for the SERT in the pathophysiology of suicide. This paper provides a review of several studies that have evaluated the role of the SERT in the pathophysiology of suicide.

Molecular genetics in the analysis of suicide

Each year, one million people die of suicide. Among the different identified risk factors, genetic factors seem to be part of a multidimensional behavior, including psychiatric, psychosocial, biological factors and physical illness. Family studies have provided evidence for familial transmission in suicide, confirmed in twin and adoption studies. At a molecular level, serotonin seems to be one of the key neurotransmitters implicated in suicidal behavior. Therefore, genes coding for proteins involved in serotonergic neurotransmission have been extensively studied in case-control association studies on suicide. Major findings concern Tryptophan hydroxylase (TPH) gene, particularly in violent suicidal behavior. Though they may seem contradictory, studies on Serotonin transporter (5-HTT), Monaomine oxidase (MAOA), Serotonin 2A and 2C receptors (5-HT2A and 5-HT2C) and Tyrosine hydroxylase (TH) genes are promising. In spite of those observations having some limitations, it appears that genetic factors are a serious risk factor, besides environmental aspects of suicidal behavior.

Serotonin brain circuits involved in major depression and suicide

Throughout his life and his work, Cajal realized the potential of the neurons he was so carefully studying and how, grouped in systems, they served the special senses and the maintenance and proper functioning of the organism. Over the past 25 years, major depression and suicide have come to be recognized as associated with alteration in serotonergic neurons and their target receptors. We examined whether prefrontal cortical (PFC) serotonin transporter sites (SERT) differ in major depression and suicide by quantitative receptor autoradiography. Clinical information was obtained by psychological autopsy. We found regionally distinct neurobiological correlates of major depression and suicide. A diffuse reduction of SERT binding throughout the dorsoventral extent of the PFC in major depression may reflect a widespread impairment of serotonergic function consistent with the range of psychopathology in major depression. The localized reduction in SERT binding in ventral PFC found in suicide victims may reflect reduced serotonin input to that brain region, underlying the predisposition to act on suicidal thoughts. It is conceivable that Cajal envisioned that psychiatric illness would be the result of "psychic neuron" pathophysiology. Today's informed psychiatrists will not be able to deny the role of the brain in the mental ailments that afflict their patients.

Alterations in serotonin transporter expression in brain regions of rats exposed neonatally to chlorpyrifos

Chlorpyrifos (CPF), one of the most widely-used organophosphate pesticides, is a suspected neuroteratogen. We administered CPF to neonatal rats on postnatal days (PN) 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), treatments devoid of overt toxicity. At the end of the treatment period (PN5 and 15, respectively) and 5-7 days later, we then examined the effects on paroxetine (PXT) binding to the presynaptic 5HT high-affinity transporter, a marker for serotonin (5HT) projections. In males, we found a persistent decrease in PXT binding across the two different treatment regimens, with deficits apparent in a brain region containing 5HT terminal fields (forebrain) as well as in a region containing 5HT cell bodies (brainstem). In contrast, females given the early treatment regimen (PN1-4) showed deficits in the brainstem but transient elevations in the forebrain; the later treatment regimen (PN11-14) had no significant effect on PXT binding in females. These data are consistent with earlier work showing brainstem cell injury resulting from neonatal CPF exposure, and indicate specific damage to 5HT neurons, with a consequent loss of transporter expression in both terminal fields and perikarya. In females, the damage may be temporarily offset by initial trophic effects in the terminal region, consequent to the cholinergic stimulation evoked by cholinesterase inhibition via the active metabolite, CPF oxon. The gender-selective effects on 5HT systems are likely to contribute to similar gender dimorphism in behavioral performance. Because the CPF effects involve 5HT, a neurotransmitter intimately involved in the control of mood, we suggest the need to evaluate behaviors that typify animal models of depression.

Decreased platelet [3H]paroxetine binding sites in suicide attempters

Research to date would suggest the possible involvement of the serotonin (5-HT) system in the pathophysiology of suicide. With this study, we aimed to investigate the platelet 5-HT transporter, by means of the specific binding of tritiated paroxetine ([3H]Par), in a sample of 20 suicide attempters recruited at a first-aid service, as compared with healthy control subjects and psychiatric patients with no current or previous history of suicide attempt. The results, showing a decreased number of [3H]Par binding sites in suicide attempters, would suggest the involvement of the presynaptic 5-HT transporter in self-aggressive behavior.

Anxiety/aggression--driven depression. A paradigm of functionalization and verticalization of psychiatric diagnosis

A new subtype of depression is proposed, named: anxiety/aggression-driven depression. The psychopathological, psychopharmacological and biochemical evidence on which this construct is based, is being discussed. Selective postsynaptic 5-HT1A agonists together with CRH and/or cortisol antagonists are hypothesized to be a specific biological treatment for this depression type, in conjunction with psychological interventions to raise the stressor-threshold and to increase coping skills. The development of this depression construct has been contingent on the introduction of two new diagnostic procedures, called functionalization and verticalization of psychiatric diagnosis. These procedures are explained and it is stressed that they are essential to psychiatric diagnosing, in order to put this process on a scientific footing.

The serotonin transporter in the midbrain of suicide victims with major depression

BACKGROUND

The involvement of serotonin in depression and suicide has been proposed, because major depression is successfully treated by medications that specifically block the serotonin transporter, and there is evidence for a decrease in serotonin transporters in major depression and suicide. The midbrain dorsal raphe nucleus (DR) has been implicated as a site for diminished serotonergic activity in that suicide victims with major depression have a significant increase in serotonin-1A autoreceptors in the DR.

METHODS

[(3)H]Paroxetine was used to label the serotonin transporter in the subnuclei of the DR at several rostral-to-caudal levels of the midbrain in ten pairs of suicide victims with major depression and age-matched psychiatrically normal control subjects.

RESULTS

There was a significant increase in serotonin transporters in the entire DR progressing from rostral-to-caudal levels in both normal control subjects and suicide victims with major depression. At comparable rostral-to-caudal levels, there were no significant differences in [(3)H]paroxetine binding between depressed suicide victims and normal control subjects in either the entire DR or its constituent subnuclei.

CONCLUSIONS

The pathophysiology of serotonin mechanisms in suicide victims with major depression does not appear to involve alterations in the binding of [(3)H]paroxetine to the serotonin transporter in the midbrain DR.

The biology of impulsivity and suicidality

Abnormalities of 5-HT and noradrenergic functioning have been implicated in aggressive impulsivity, SIB, and suicidal behavior. The role of DA and GABA in human studies of these behaviors requires further investigation. Most studies suggest that impulsive aggression is related to lower levels of CNS 5-HT. Some studies demonstrate that increasing NE correlates to impulsive aggression, whereas other studies demonstrate an opposite relationship. The role of NE in impulsive aggressive behavior is still unclear. Self-injurious behavior is similar to impulsive aggression in that it seems to be mediated by the neurotransmitter systems previously mentioned. For example, the presence of lower levels of 5-HT and abnormalities in the DA system are related to SIB in patients with BPD and depression. SIB severity also seems to be influenced by neglect (e.g., severe isolation during rearing). As animal studies suggest, increasing the amount of isolation and an earlier onset of isolation increase the severity of SIB. Suicidal behaviors and the lethality of suicide attempts may also be linked to the abnormalities in neurotransmitter systems similar to those found in patients with impulsive aggression and SIB, namely, lowered 5-HT transmission and enhanced DA and NE functioning. Understanding the biological triggers of impulsive aggression or SIB may allow for the evaluation of suicidal attempts and completion from a different perspective and, in conjunction with genetic predictors, may eventually help with the early prediction and prevention of suicidal behaviors. Additional studies of live subjects and postmortem brains will assist in clarifying the neurobiology of suicidal behaviors that are common to many disorders and are clinically relevant to BPD.

Morphometry of the dorsal raphe nucleus serotonergic neurons in suicide victims

BACKGROUND

The serotonin deficiency hypothesis of suicide has been important heuristically. Few studies have directly examined the brainstem dorsal raphe nucleus (DRN) serotonin neurons. We determined the number and morphometry of DRN serotonergic neurons in suicide victims (n = 7) compared to controls (n = 6).

METHODS

Brainstems were collected at autopsy, fixed and cryoprotected. Tissue was sectioned, stained for Nissl and processed with an antiserum that cross-reacts with tryptophan hydroxylase. All DRN neurons were identified, counted and analyzed every 1000 microns. Neuron morphometry was characterized by soma area (micron 2), sphericity, perimeter, length and density (neurons per mm3).

RESULTS

Neuron number and density was higher in suicide victims (1,780 +/- 127 neurons/mm3) than controls (1,349 +/- 68). The DRN volume did not differ between groups (66 +/- 9 mm3 for controls vs. 67 +/- 5 mm3 for suicides). Mean neuronal area and sphericity did not differ between suicides and controls. The total number and the density of DRN neurons did not correlate with age.

CONCLUSIONS

The finding of an increased number of neurons indicates that impaired serotonergic transmission found in association with serious suicide attempts is not due to fewer neurons.

Neuropathology of suicide. A review and an approach

Neuropathology is one approach to the effort to elucidate the pathophysiology of suicide. Initial neurochemical studies focusing on the roles of serotonin (5-HT) and noradrenaline (NE) abnormalities in brains of suicide victims have been somewhat inconsistent. More recently developed methodologies, including quantitative receptor autoradiography, immunoblotting, immunohistochemistry, cell morphometry, in situ hybridization, Northern analysis, solution hybridization/RNase protection assay, reverse transcriptase polymerase chain reaction, and genotyping, which have already been applied successfully in studies of other disorders of brain structure or function, are now increasingly being adopted for postmortem studies of suicide. These new strategies are adding convergent evidence for brain 5-HT and NE dysfunction in the etiology of suicide susceptibility, refining the neuroanatomical localization of this dysfunction, and in addition, implicating heretofore unsuspected candidate neurotransmitter systems in the neuropathological substrates of suicide susceptibility. It is argued here that the confluence of the availability of suitable postmortem samples and this augmentation of our armamentarium of techniques promises the attainment of important new insights into the biological underpinnings of suicide from postmortem research. It is to be hoped that this new knowledge might inspire novel pharmacotherapeutic strategies for the prevention of suicide.

Postmortem findings in suicide victims. Implications for in vivo imaging studies

Alterations in serotonergic and noradrenergic receptor binding in membrane homogenates from the brain of suicide victims suggest a biological substrate for the vulnerability to commit suicide. We and others have employed high-resolution quantitative autoradiography of full coronal sections of the prefrontal cortex to map the locus of maximal change in receptor binding. We found alterations in binding to the serotonin transporter, the 5-HT1A, and the 5-HT2A receptors primarily in the ventral and ventrolateral prefrontal cortex of suicide victims. Importantly, these changes are often modest in magnitude and anatomically restricted to one or two Brodmann areas. Furthermore, we have found that care in case selection is essential, because sex, age, drugs, and comorbid diagnoses contribute to receptor binding. The implications for in vivo imaging are considerable, directing the focus of such studies toward the ventrolateral prefrontal cortex. However, because ligands are limited, as is the resolution of current methods, including PET, automated analyses that produce statistical images, rather than manual selection of individual slices, will likely lack the ability to detect the discrete receptor changes found postmortem. Alternatively, the advantages of examining large numbers of subjects, imaging the entire brain, obtaining detailed clinical information in the living patient, and magnifying the changes with neuropharmacological challenges present a promising outlook for making major advances into the identification of brain abnormalities associated with suicide risk.

Biologic alterations in the brainstem of suicides

This article reviews the data supporting the notion that there are alterations in serotonin and norepinephrine in the ventral prefrontal cortex and brainstem of suicide victims. Normal amounts of serotonin are found in terminal fields such as the dorsolateral prefrontal cortex, but serotonin responses are defective at least in the hypothalamus. Suicide victims appear to have fewer noradrenergic LC neurons, containing more of the tyrosine hydroxylase enzyme needed for transmitter synthesis. A failure of behavior restraint mechanisms involving the prefrontal cortex as a consequence of alterations in brainstem monoaminergic nuclei may result in a predisposition to suicidal behavior.