Neuropathology of suicide. A review and an approach

Modeling endophenotypes of suicidal behavior in animals

Suicide is a major public health concern. One of the common contributors to the increased risk for suicide is the genetic constitution of individuals, which determines certain endophenotypic traits used as quantifiable measure of neurobiological functions. Therefore, a logical deconstruction of the originating endophenotypes associated with suicidal risk could provide a better understanding of this complex disorder. In this regard, non-human animals can be a useful resource to test endophenotypes of suicidal behavior and the neurobiology underlying these endophenotypes. In this review, we have focused on the neurobiological abnormalities, primarily genetic and epigenetic abnormalities, associated with suicidal behavior and the scope of their modeling in animals. This can substantially advance the current understanding of suicidal behavior manifested with certain trait-based endophenotypes and may provide an opportunity to test novel hypotheses as well as aid in the development of treatment opportunities and risk assessment.

Neuropathological changes in the substantia nigra in schizophrenia but not depression

Schizophrenia is a chronic, disabling neuropsychiatric disorder characterised by positive, negative and cognitive symptoms. The aetiology is not known, although genetic, imaging and pathological studies have implicated both neurodevelopmental and neurodegenerative processes. The substantia nigra is a basal ganglia nucleus responsible for the production of dopamine and projection of dopaminergic neurons to the striatum. The substantia nigra is implicated in schizophrenia as dopamine has been heavily implicated in the dopamine hypothesis of schizophrenia and the prevalent psychotic symptoms and the monoamine theory of depression, and is a target for the development of new therapies. Studies into the major dopamine delivery pathways in the brain will therefore provide a strong base in improving knowledge of these psychiatric disorders. This post-mortem study examines the cytoarchitecture of dopaminergic neurons of the substantia nigra in schizophrenia (n = 12) and depression (n = 13) compared to matched controls (n = 13). Measures of nucleolar volume, nuclear length and nuclear area were taken in patients with chronic schizophrenia and major depressive disorder against matched controls. Astrocyte density was decreased in schizophrenia compared to controls (p = 0.030), with no change in oligodendrocyte density observed. Significantly increased nuclear cross-sectional area (p = 0.017) and length (p = 0.021), and increased nucleolar volume (p = 0.037) in dopaminergic neurons were observed in schizophrenia patients compared with controls, suggesting nuclear pleomorphic changes. No changes were observed in depression cases compared to control group. These changes may reflect pathological alterations in gene expression, neuronal structure and function in schizophrenia.

The association between suicidality and serotonergic dysfunction in depressed patients

The loudness dependence of auditory evoked potentials (LDAEP) has been proposed as a reliable indicator of central serotonin system activity in animal and some human studies. Since low central serotonergic activity is related to suicidality, it is possible that the LDAEP can be used to predict suicidality. The aim of the present study was to determine whether there is an association between suicidality and LDAEP in a depressed Korean population. Data from 38 depressive subjects (10 males, 28 females; mean age: 40.79 years) were analyzed. The subjects were divided into two groups: with prior suicide attempts (SA; n=17) and no prior suicide attempts (NSA; n=21). The LDAEP was evaluated by measuring auditory event-related potentials. Peak-to-peak N1/P2 amplitudes were calculated at five stimulus intensities, and the LDAEP was calculated as the slope of the linear-regression curve. The LDAEP values differed significantly between the SA and NSA groups. Depressed subjects with a history of suicide attempts seem to be characterized by large LDAEP values, indicating low serotonergic activity. The findings of the present study support the view that low serotonergic activity is related to the suicidality of depressed subjects. Thus, LDAEP, which can reflect serotonergic activity, may be a practical biological marker for suicidality.

Anger- and aggression-related traits are associated with polymorphisms in the 5-HT-2A gene

BACKGROUND

This study investigates the association of four single nucleotide polymorphisms (SNPs) in the serotonin 2A (5-HT-2A) receptor gene with anger-, aggression- and suicide-related behavior in a total of 566 subjects (203 German suicide attempters and 363 German community-based healthy volunteers).

METHODS

Anger- and aggression-related traits were assessed by using the State Trait Anger Expression Inventory (STAXI) and the Questionnaire for Measuring Factors of Aggression (FAF).

RESULTS

Three (rs643627-rs594242-rs6311: A-C-T), two (rs594242-rs6311: C-T) and a single functional (rs6311: T) marker were protective against suicidal behavior. The complementary makers (rs594242-rs6311: G-C and rs6311: C) were associated with increased risk for non-violent (p=0.01; p=0.009 respectively) and impulsive suicidal behavior (p=0.03; p=0.01 respectively). Furthermore, CC-homozygotes for the functional SNP rs6311 reported more anger- (p=0.004) and aggression-related behavior (p=0.011).

CONCLUSION

We conclude that variations in the 5-HT-2A gene may modify the phenotype of suicide-, anger-, and aggression-related behavior. Further studies should especially focus on intermediate personality traits in this context.

Lower cerebrospinal fluid homovanillic acid levels in depressed suicide attempters

BACKGROUND

Studies suggest that the dopaminergic system is involved in the pathogenesis of major depression, Axis II disorders, and suicidal behavior. Depressed suicide attempters constitute a heterogenous group and important differences may exist between depressed suicide attempters with or without Axis II disorders. Therefore, we compared demographic and clinical parameters, and cerebrospinal fluid (CSF) homovanillic acid (HVA) levels in depressed suicide attempters without comorbid Axis II disorders, depressed non-attempters without comorbid Axis II disorders, and normal controls.

METHODS

Thirty-one depressed subjects with a history of a suicide attempt, 27 depressed subjects without a history of a suicide attempt, and 50 healthy controls were included in the study. Subjects with comorbid Axis II disorders were excluded. Demographic and clinical parameters, and CSF HVA levels were examined.

RESULTS

The two depressed groups did not differ with regard to depression, aggression, hopelessness, and total hostility scale scores. Depressed suicide attempters had higher current suicidal ideation scores compared to depressed non-attempters. Depressed suicide attempters had lower CSF HVA levels compared to depressed non-attempters (t = 4.4, df = 56, p < 0.0001) and to controls (t = -4.09, df = 79, p < 0.0001). There was no difference in CSF HVA levels between depressed non-attempters and controls (t < 1, df = 75, NS).

CONCLUSIONS

Dopaminergic abnormalities are associated with suicidality but not with depression. The variability in the rates of comorbid Axis II disorders and in the prevalence of suicide attempters in different patient populations may affect both clinical and biological results of studies of mood disorders.

Serotonin dysfunction and suicide attempts in major depressives: an auditory event-related potential study

BACKGROUND

Serotonergic dysfunction is believed to be involved in suicide attempts. The loudness-dependent auditory evoked potential (LDAEP) is one of the validated indicators of the activity of the central serotonin system in humans.

OBJECTIVES

This study was designed to investigate possible differences in the LDAEP and P300 between those depressed patients who attempted suicide and those who did not.

METHODS

The LDAEP and P300 levels were recorded for 66 depressive patients (among which 16 had attempted suicide).

RESULTS

Those who had attempted suicide showed a sharper slope of the LDAEP and increased frontal P300 amplitude. A high correlation between the LDAEP and P300, and a gender difference were also noted.

CONCLUSIONS

Our results are concordant with previous assumptions about serotonin dysfunction in depressives who attempt suicide.

Reduction of synapsin in the hippocampus of patients with bipolar disorder and schizophrenia

Several studies suggest that decreased expression of presynaptic proteins may be characteristic of schizophrenia. We examined one such protein, synapsin, in schizophrenia and bipolar disorder. Samples of hippocampal tissue from controls (n = 13), patients with schizophrenia (n = 16), or bipolar disorder (n = 6), and suicide victims (n = 7) were used. The membrane and cytosolic fractions were analyzed by Western immunoblotting for synapsin using an antibody that detects synapsin Ia, IIa, and IIIa proteins. Synaptophysin was also measured for comparison. Total synapsin was decreased significantly in patients with schizophrenia (P = 0.034) and in bipolar disorder (P = 0.00008) as compared to controls. The synapsin/synaptophysin ratios were decreased in schizophrenia and bipolar disorder, and additionally in suicide victims (P = 0.014). Age, postmortem interval, percentage of protein extracted, and pH of brain were not different between groups. No changes in total synapsin or synaptophysin in the hippocampus were produced by injecting rats with either lithium or haloperidol for 30 days. Reductions in synapsin in both patients with schizophrenia (synapsin IIa and IIIa) and bipolar disorder (synapsin Ia, IIa and IIIa) imply that altered or reduced synaptic function in the hippocampus may be involved in these disorders.

G protein-coupled receptor kinases, beta-arrestin-2 and associated regulatory proteins in the human brain: postmortem changes, effect of age and subcellular distribution

G protein-coupled receptor kinases (GRKs) and beta-arrestin-2 play a crucial role in the regulation of neurotransmitter receptors in brain. In this study, GRK2, GRK6, beta-arrestin-2 and associated regulatory proteins (Gbeta proteins and protein phosphatase (PP)-2A) were quantitated in human brains (immunodensity with specific antibodies) to assess for postmortem changes (pattern of protein degradation) and to investigate the effect of aging on these regulatory proteins as well as their subcellular distribution (cytosol and membrane fractions). In brain (prefrontal cortex, total homogenate) of healthy subjects (n=14) the immunodensities of GRK2 (r=-0.76), GRK6 (r=-0.64), beta-arrestin-2 (r=-0.57), Gbeta proteins (r=-0.59) and neurofilament (NF)-L (r=-0.64), but not PP-2A, declined markedly with the length of postmortem delay (PMD, 3-81 h). With these linear decay models, the average decreases per 12 h of PMD (from 12 to 72 h) were 7-11% for the various proteins. The immunodensities of GRK2 (r=-0.71), GRK6 (r=-0.61), and beta-arrestin-2 (r=-0.54) in human brain (n=12) also declined with aging (16 to 87 years) and the average decreases per decade (from 20 to 80 years) were 3-5%. In contrast, the immunodensities of PP-2A, Gbeta and NF-L in brain did not correlate significantly with the age of the subject at death (16-87 years). The immunodensities of GRK2/6 and beta-arrestin-2 showed marked individual variations and were strongly reduced after several freeze/thaw cycles. In the prefrontal cortex the subcellular distribution (cytosol/membrane) of the two GRKs differed markedly (GRK2: 60%/40%; GRK6: 5%/95%), and that of beta-arrestin-2 was as expected for a soluble protein (60%/40%). In brains of healthy subjects, the immunodensities of cytosolic GRK2 and beta-arrestin-2 correlated, respectively, with those of membrane-associated GRK2 (r=0.67, P=0.049, n=9) and membrane-associated beta-arrestin-2 (r=0.77, P=0.01, n=9). The results of this study emphasize the importance of examining relevant variables (PMD, age) and potential artifacts (individual variation, freeze-thawing effect) when designing signal transduction studies in neuropsychiatric disorders using the postmortem human brain.

Understanding the neurobiology of suicidal behavior

Our current knowledge about the neurobiology of suicide is still limited. Technical limitations and the complexity of the CNS are major obstacles. However, there is evidence for a hereditary disposition to suicide, which appears to be independent of diagnosis. Clinical, postmortem, genetic, and animal studies suggest that serotonin has a central role. The main regions of interest in the CNS have been the dorsal and median raphe nuclei in the midbrain that host the main serotonergic cell bodies and the prefrontal cortex, particularly the ventral PFC, innervated by the serotonergic system. In vivo and postmortem studies indicate serotonergic hypofunction in suicide and serious suicide attempts. This deficiency in turn can lead to a predisposition to impulsive and aggressive behavior, probably due to a breakdown in the inhibitory function of the ventral prefrontal cortex as a result of less serotonin input. In the context of this predisposition and the development of mental illness or other life stressors, the individual is at risk of acting on suicidal thoughts. Such deficient serotonin input into the PFC may arise as a result of genetic, parenting, head injury, and other effects. Identifying psychiatric, social, and environmental predictors of suicide are studied to improve prediction and prevention of suicide. A better understanding of the neurobiology of suicide can help detect at risk populations and help develop better treatment interventions.

Suicide and Alzheimer's pathology in the elderly: a case-control study

BACKGROUND

The single most important risk factor for Alzheimer's pathology is age. Elderly individuals are also at increased risk for suicide, but comprehensive studies of the association between Alzheimer's pathology and suicide are lacking. We designed the current study to determine if Alzheimer's disease changes are overrepresented in elderly people committing suicide.

METHODS

The design is a case-control study. Cases (n = 28) were subjects older than 60 years of age who completed suicide. For each case, two age- and gender-matched individuals who died naturally were selected as control subjects (n = 56). Neuropathologic examination of hippocampal sections was performed blindly and included a modified Braak scoring system and semiquantitative assessment of neurofibrillary tangles, amyloid deposition, Lewy bodies, and Lewy-associated neurites. Data were analyzed by conditional logistic regression.

RESULTS

The brains of individuals who committed suicide had higher modified Braak scores than those of matching control subjects (p =.0028). The number of neurofibrillary tangles in CA1 was not an independent predictor of suicide status in the statistical analysis (p =.16), although the distribution was more highly skewed among the cases (75th percentile of 10.5 for cases, vs. 2 for control subjects).

CONCLUSIONS

Severe Alzheimer's disease pathology is overrepresented in elderly patients who complete suicide.