Serotonergic function and suicidal behavior in personality disorders

Vitamin D and the omega-3 fatty acids control serotonin synthesis and action, part 2: relevance for ADHD, bipolar disorder, schizophrenia, and impulsive behavior

Serotonin regulates a wide variety of brain functions and behaviors. Here, we synthesize previous findings that serotonin regulates executive function, sensory gating, and social behavior and that attention deficit hyperactivity disorder, bipolar disorder, schizophrenia, and impulsive behavior all share in common defects in these functions. It has remained unclear why supplementation with omega-3 fatty acids and vitamin D improve cognitive function and behavior in these brain disorders. Here, we propose mechanisms by which serotonin synthesis, release, and function in the brain are modulated by vitamin D and the 2 marine omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Brain serotonin is synthesized from tryptophan by tryptophan hydroxylase 2, which is transcriptionally activated by vitamin D hormone. Inadequate levels of vitamin D (∼70% of the population) and omega-3 fatty acids are common, suggesting that brain serotonin synthesis is not optimal. We propose mechanisms by which EPA increases serotonin release from presynaptic neurons by reducing E2 series prostaglandins and DHA influences serotonin receptor action by increasing cell membrane fluidity in postsynaptic neurons. We propose a model whereby insufficient levels of vitamin D, EPA, or DHA, in combination with genetic factors and at key periods during development, would lead to dysfunctional serotonin activation and function and may be one underlying mechanism that contributes to neuropsychiatric disorders and depression. This model suggests that optimizing vitamin D and marine omega-3 fatty acid intake may help prevent and modulate the severity of brain dysfunction.

Is there a shared neurobiology between aggression and Internet addiction disorder?

PURPOSE

Evidences indicate that Internet addiction disorder (IAD) has a higher risk of developing aggression and violent behavior. A few correlation studies between IAD and aggression have implicated a common biological mechanism. However, neurobiological approaches to IAD and aggression have not yet been studied.

METHODS

A literature search for studies for Internet addiction disorder or aggression was performed in the PubMed database and we selected articles about neurobiology of IAD or aggression.

RESULTS

This review includes (a) common neural substrates such as the prefrontal cortex and the limbic system between aggression and IAD; (b) common neuromodulators such as dopamine, norepinephrine, serotonin, opiate and nicotine between aggression and IAD.

CONCLUSIONS

Through reviewing the relevant literature, we suggested the possibility of common neurobiology between the two psychiatric phenomena and direction of research on aggression in IAD.

Loudness dependence of auditory evoked potentials (LDAEP) in clinical monitoring of suicidal patients with major depression: a pilot study

Loudness dependence of auditory evoked potentials (LDAEP) is a validated in vivo marker of central serotonergic function. We aimed at measuring serotonergic activity in a follow-up study of suicidal patients. It should be investigated whether suicide attempts or suicidal states cause changes in the LDAEP. Thirteen patients (mean age, 40.9 ± 11.3 years; age range, 20-61, 6 male) with a major depressive episode who had attempted suicide or had suicidal plans (Hamilton Depression Rating Scale item 3 [suicidality] ≥3) were included in the study. LDAEP and psychometric measurements took place about 2, 5, 9 and 16 days after attempted suicide or suicidal action. On day 9, LDAEP was significantly higher compared to day 2 and day 16; there was a similar tendency compared to day 5. Instability of central serotonergic function is suggested resulting in reduced serotonergic activity about 1 week after suicide attempt. Further studies are necessary that include larger samples in order to distinguish between different psychiatric diseases and to consider confounding factors like gender, smoking, medication, impulsivity or lethality of suicidal action.

Recent advances in the biological study of personality disorders

While it is premature to provide a simple model for the vulnerability to the development of either borderline (BPD) or schizotypal (SPD) personality disorder, it is clear that these heritable disorders lend themselves to fruitful neurobiological exploration. The most promising findings in BPD suggest that a diminished top-down control of affective responses, which is likely to relate to deceased responsiveness of specific midline regions of prefrontal cortex, may underlie the affective hyperresponsiveness in this disorder. In addition, genetic and neuroendocrine and molecular neuroimaging findings point to a role for serotonin in this affective disinhibition. Clearly SPD falls within the schizophrenia spectrum, but precisely the nature of what predicts full-blown schizophrenia as opposed to the milder symptoms of SPD is not yet clear.

Serotonergic responses in depressed patients with or without a history of alcohol use disorders and healthy controls

Dysfunction of serotonergic neurotransmission has been implicated in the etiopathogenesis of major depression (MDD) and alcohol use disorders (AUD). To compare serotonin function in MDD with co-occurring AUD (MDD/AUD), MDD without co-occurring AUD (MDD only) and healthy controls (HC) we sought to study differences in prolactin responses to fenfluramine administration in patients with MDD/AUD, patients with MDD only and HC. In all, 169 subjects (62 MDD/AUD, 75 MDD only, and 32 HC) were entered into the study. Controlling for gender, prolactin responses were lower in the MDD/AUD group compared to the MDD only or the HC group. Controlling for gender and aggression, prolactin responses in the MDD/AUD group remained significantly lower compared to the HC group but the difference between the MDD/AUD and the MDD only groups disappeared. The difference in prolactin responses between MDD/AUD and MDD only could be attributed to higher aggression scores in the MDD/AUD group compared to the MDD group.

Neural systems implicated in delayed and probabilistic reinforcement

This review considers the theoretical problems facing agents that must learn and choose on the basis of reward or reinforcement that is uncertain or delayed, in implicit or procedural (stimulus-response) representational systems and in explicit or declarative (action-outcome-value) representational systems. Individual differences in sensitivity to delays and uncertainty may contribute to impulsivity and risk taking. Learning and choice with delayed and uncertain reinforcement are related but in some cases dissociable processes. The contributions to delay and uncertainty discounting of neuromodulators including serotonin, dopamine, and noradrenaline, and of specific neural structures including the nucleus accumbens core, nucleus accumbens shell, orbitofrontal cortex, basolateral amygdala, anterior cingulate cortex, medial prefrontal (prelimbic/infralimbic) cortex, insula, subthalamic nucleus, and hippocampus are examined.

Brain perfusion SPECT in impulsivity-related personality disorders

BACKGROUND

Impulsive behaviours in patients with cluster B personality disorders are associated with low glucose metabolism and regional cerebral blood flow in the frontal cortex and subcortical structures. The aim of this study is to confirm the presence of a particular pattern of brain perfusion in a sample of borderline (BPD) and anti-social personality disorder (ASPD) patients using brain perfusion single photon emission computed tomography (SPECT).

METHODS

A brain perfusion SPECT study was performed in 37 patients with BPD or ASPD (and no Axis I diagnosis) and 34 healthy control participants. Data were acquired on a triple head Toshiba gamma camera. Scatter and attenuation correction was done. Reconstructed SPECT images were analyzed by Statistical Parametrical Mapping (SPM99).

RESULTS

There were no significant differences in age and gender distributions between the patients and the healthy controls. With regard to the functional imaging results, patients were characterized by a reduced regional cerebral blood flow (rCBF) in right temporal and prefrontal brain areas, including the right lateral temporal cortex (BA 21), the right frontopolar cortex (BA 10) and the right ventrolateral prefontal cortex (BA 47).

CONCLUSIONS

Patients with BPD and ASPD who showed impulsive behaviour have diminished rCBF in areas of the right prefrontal and temporal cortex.

Low prolactin response to fenfluramine in impulsive aggression

To examine the prolactin (prl) response to d,l-fenfluramine in a large sample of personality disorder patients with impulsive aggression. Patients were screened from clinics at the Bronx VAMC and the Mount Sinai Medical Center and from press releases. One hundred and forty-six personality disorder patients (90M;56F) and 23 normal controls (15M;8F) underwent oral d,l-fenfluramine challenge. The peak change in prolactin(deltapkprl) was calculated by subtracting baseline prolactin from peak response following fenfluramine administration (3 h). Analysis of variance and regression analysis were used to detect group differences in deltapkprl. Deltapkprl in impulsive aggressive men, but not women, with personality disorders was blunted compared with controls. Men with suicide histories also had a blunted deltapkprl compared with those without, which was not accounted for by depression. This study represents a replication of previous studies, in a much larger sample, showing a blunted PRL response to fenfluramine of male patients with personality disorder in relation to impulsive aggression and to suicide attempts.

Disinhibitory behavior and GABA(A) receptor function in serotonin-depleted adult male rats are reduced by gonadectomy

Impulsive and aggressive behaviors in, e.g., personality or substance abuse disorders in man and corresponding behaviors in rats may involve serotonin (5-HT), gamma-amino-butyric acid(A)/benzodiazepine receptor complexes (GABA(A)/BDZ-RC) and steroid hormones, e.g., testosterone. Here, we studied the effect of gonadectomy on disinhibitory behavior in individually housed 5-HT-depleted rats and on GABA(A)/BDZ-RC function in vitro, in corticohippocampal synaptoneurosomes prepared from the brain of these animals. 5-HT depletion by intracerebroventricular 5,7-dihydroxytryptamine (5,7-DHT)-induced disinhibitory behavior in a shock-induced behavioral inhibition model (punished conflict model) 14 days after operation. Gonadectomy in connection with the 5-HT depletion reduced the disinhibitory behavior and testosterone substitution prevented this effect. Shock threshold and drinking motivation were not affected by gonadectomy and/or 5-HT depletion. The relative epididymides weight was increased in 5-HT-depleted as compared to sham-operated rats. However, the serum concentrations of testosterone and the relative testes weights were not different in 5-HT-depleted rats as compared to controls. GABA-induced (30, 100, 300 microM) 36Cl(-)-uptake into synaptoneurosomes was lower in 5,7-DHT+gonadectomized rats compared to the control group. This effect was reversed by substitution with testosterone. These results demonstrate that gonadectomy reduces disinhibitory behavior in 5-HT-depleted rats and that GABA(A)/BDZ-RC may be involved in this effect.

Serotonin transporter gene polymorphisms, alcoholism, and suicidal behavior

BACKGROUND

Dysfunction of serotoninergic transmission could predispose to excessive alcohol consumption and dependence. The functional polymorphism of the serotonin transporter gene (5-HTTLPR) has been associated with different disorders, including alcoholism. Considering the likelihood of heterogeneity in the "alcohol dependence" phenotype, 5-HTTLPR may be more specifically implicated in subsamples of patients or in related traits of alcoholism, such as impulsivity.

METHODS

We analyzed the role of this functional polymorphism in the risk for suicide attempt in a population of male alcohol-dependent subjects. One hundred ten male alcohol-dependent patients (DSM-III-R criteria), French for at least two generations, were personally interviewed with the Diagnostic Interview for Genetic Studies and compared with 61 unaffected blood donors.

RESULTS

The "short" (S) allele of the 5-HTTLPR appeared to be unrelated to alcohol dependence and comorbid depression in our sample, but was found associated with an increased risk for suicide attempts. This association was predominantly observed in severe and repetitive suicide attempts, with a significant dose effect of the S allele (0, 1, or 2) on the number and the severity of suicide attempts.

CONCLUSIONS

Mood disorders and alcohol dependence may interact with a genetic (relative) deficiency in serotonin reuptake, thereby increasing the risk for aggressive/impulsive behaviors such as suicide attempts.

Gonadectomy enhances shock-induced behavioral inhibition in adult male rats: implications for impulsive behavior

The effects of gonadectomy on shock-induced behavioral inhibition in a modified Vogel's drinking conflict model and on diazepam-induced disinhibition and sedation were investigated in adult male rats. Gonadectomy enhanced shock-induced behavioral inhibition when determined 9, 21, 45, and 65 days, but not 3 days, after operation, without affecting shock sensitivity or drinking motivation. Testosterone-substitution for 21 days following gonadectomy prevented this enhanced inhibition without significantly affecting the behavior in sham-operated rats. Diazepam produced behavioral disinhibition both in sham-operated and gonadectomized rats. However, after the highest dose (16 mg/kg, IP) the disinhibited behavior decreased only in sham-operated animals, most likely due to sedation. Moreover, whereas there was no difference in basal rotarod-performance between controls and gonadectomized rats, the latter animals were less sensitive to diazepam-induced disruption of rotarod walking ability. Sham-operated or gonadectomized animals did not differ with respect to serum diazepam levels at the postinjection times used in the behavioral tests. Taken together, gonadectomized rats were less sensitive towards diazepam-induced sedation, possibly due to a subsensitivity at or beyond GABA(A)/benzodiazepine receptors. Furthermore, the finding that lack of testosterone enhanced shock-induced inhibition could be interpreted to reflect increased impulse control and may involve an altered activation of GABA(A)/benzodiazepine receptors.

A fenfluramine-activated FDG-PET study of borderline personality disorder

BACKGROUND

Impulsive aggression in patients with personality disorders is associated with diminished levels of cerebrospinal fluid (CSF) 5-HIAA, blunted neuroendocrine responses to serotonergic agonists, and decreased glucose utilization in the prefrontal cortex. We tested the hypothesis that impulsive aggression in borderline personality disorder (BPD) may be associated with diminished serotonergic regulation in the prefrontal cortex, using positron-emission tomography (PET) neuroimaging during pharmacologic challenge with d,l fenfluramine (FEN).

METHODS

A 2-day, single-blind, placebo-controlled FEN challenge study was conducted in five patients with BPD (and no Axis I MDD) and eight healthy control participants. On Day 1, 4 mCi [(18)F]-fluorodeoxyglucose (FDG) was injected 3 hours after ingestion of placebo; on Day 2, FDG was injected 3 hours after ingestion of.8 mg/kg to 60 mg of d,l fenfluramine. After 30 min, a 45-min emission scan was acquired on the Siemans/CTI 951r/31 scanner. PET data were aligned to MR images and analyzed by Statistical Parametric Mapping (SPM96).

RESULTS

In response to placebo, uptake of FDG was greater in control participants than patients in large areas of the prefrontal cortex including medial and orbital regions bilaterally (BA 10-11), left superior temporal gyrus, and right insular cortex. There were no areas in which patients had greater relative regional uptake than control participants. In response to FEN, relative regional uptake of FDG (relative to placebo) was greater in control participants compared to patients in medial and orbital regions of right prefrontal cortex (BA 10), left middle and superior temporal gyri (BA 22-23), left parietal lobe (BA 40), and left caudate body.

CONCLUSIONS

Patients with BPD have diminished response to serotonergic stimulation in areas of prefrontal cortex associated with regulation of impulsive behavior.

Recreational use of "ecstasy" (MDMA) is associated with elevated impulsivity

Recent preclinical evidence suggests that repeated exposure to 3, 4-methylenedioxy-methamphetamine (MDMA; "ecstasy") produces long-term reductions in serotonin (5-HT) levels. 5-HT has been implicated in the regulation of mood, anxiety, aggression, impulsivity, and cognition. Accordingly, in the first of two separate studies, these variables were investigated in three groups: (1) MDMA group--recreational ecstasy users (who also used other illicit substances); (2) polydrug controls--who had never taken ecstasy, but otherwise had drug histories and personal characteristics similar to the ecstasy users; and (3) nondrug controls--who had never used illicit drugs, but had similar personal characteristics. All participants completed mood (Likert) scales, personality questionnaires (which included the impulsiveness, venturesomeness and empathy questionnaire-IVE), spatial span and "Tower of London" (TOL) tests, and a behavioural measure of impulsivity, the matching familiar figures test (MFF20). There were no group differences in mood, anxiety, anger/hostility, and cognitive performance, but the MDMA group committed significantly more errors in the MFF20. Subsequently, a larger sample of participants were administered mood (the General Health Questionnaire or GHQ) and personality (IVE) questionnaires before the administration of a TOL test, followed by the MFF20, and a second TOL test. Although there were no group differences in TOL performance, ecstasy users were again found to commit more errors in the MFF20 than polydrug users. Furthermore, the GHQ and IVE scores of the ecstasy users in the second study indicated, respectively, that they were more psychologically disturbed and impulsive than nondrug controls. The combined data from the two studies indicated that ecstasy users exhibited elevated impulsivity on both self-report and behavioral measures and that those who had taken the most ecstasy had the most elevated trait impulsiveness scores. These findings are consistent with previous evidence that elevated levels of impulsivity in humans are associated with reduced levels of serotonergic function.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.