Dopamine cross-sensitization between psychostimulant drugs and stress in healthy male volunteers

Dysregulation of the stress response system is a potential etiological factor in the development of and relapse to multiple neuropsychiatric disorders. Previously we reported that repeated intermittent d-amphetamine administration can lead to progressively greater dopamine release, thereby providing evidence of drug-induced neurochemical sensitization. Here, we test the hypothesis that repeated exposure to d-amphetamine increases dopaminergic responses to stress; that is, produces cross-sensitization. Using positron emission tomography, we measured in 17 healthy male volunteers (mean ± s.d. = 22.1 ± 3.4 years) [(11)C]raclopride binding responses to a validated psychosocial stress task before and 2 weeks after a regimen of repeated d-amphetamine (3 × 0.3 mg kg(-1), by mouth; n = 8) or placebo (3 × lactose, by mouth; n = 9). Mood and physiological measurements were recorded throughout each session. Before the d-amphetamine regimen, exposure to the stress task increased behavioral and physiological indices of stress (anxiety, heart rate, cortisol, all P ⩽ 0.05). Following the d-amphetamine regimen, the stress-induced cortisol responses were augmented (P < 0.04), and voxel-based analyses showed larger stress-induced decreases in [(11)C]raclopride non-displaceable binding potential across the striatum. In the placebo group, re-exposure to stress led to smaller clusters of decreased [(11)C]raclopride binding, primarily in the sensorimotor striatum (P < 0.05). Together, this study provides evidence for drug × stress cross-sensitization; moreover, random exposure to stimulants and/or stress cumulatively, while enhancing dopamine release in striatal areas, may contribute to a lowered set point for psychopathologies in which altered dopamine neurotransmission is invoked.

Limbic system mGluR5 availability in cocaine dependent subjects: a high-resolution PET [(11)C]ABP688 study

Cocaine self-administration decreases type 5 metabotropic glutamate receptor (mGluR5) tissue concentrations in laboratory rats during early abstinence. These changes are thought to influence the drug's reinforcing properties and the ability of drug-related cues to induce relapse. Here, our goal was to measure brain regional mGluR5 availability in recently abstinent cocaine dependent humans. Participants meeting DSM-IV diagnostic criteria for current cocaine dependence (n=9) were recruited from the general population. mGluR5 availability (binding potential, non-displaceable; BPND) was measured with high-resolution positron emission tomography (PET HRRT) and [(11)C]ABP688. Compared to age- and sex-matched healthy controls (n=9), cocaine dependent subjects showed significantly lower BPND values in the ventral (bilateral: -28.2%, p=0.011), associative (right: -21.4%, p=0.043), and sensorimotor striatum (bilateral: -21.7%, p=0.045), amygdala (left: -26%, p=0.046) and insula (right: -23.3%, p=0.041). Among the cocaine users, receptor availabilities were related to abstinence (range: 2 to 14days). The longer the duration of abstinence, the lower the BPND values in the sensorimotor striatum (r=-0.71, p=0.034), left amygdala (r=-0.73, p=0.026) and right insula (r=-0.67, p=0.046). Compared to healthy controls, BPND values were significantly reduced in those who tested negative for cocaine on the PET test session in the ventral (p=0.018) and sensorimotor striatum (p=0.017), left amygdala (p=0.008), and right insula (p=0.029), but not in those who tested positive. Together, these results provide evidence of time-related mGluR5 alterations in striatal and limbic regions in humans during early cocaine abstinence.

Tryptophan hydroxylase(2) gene polymorphisms predict brain serotonin synthesis in the orbitofrontal cortex in humans

Brain regional serotonin synthesis can be estimated in vivo using positron emission tomography (PET) and α-[((11))C]methyl-L-tryptophan ((11)C-AMT) trapping (K*) as a proxy. Recently, we reported evidence of lower normalized (11)C-AMT trapping in the orbitofrontal cortex (OBFC) of subjects meeting the criteria for an impulsive and/or aggressive behavioral phenotype. In this study, we examined whether part of the variance in OBFC serotonin synthesis is related to polymorphisms of the gene that encodes for the indoleamine's rate-limiting enzyme in the brain, tryptophan hydroxylase-2 (TPH(2)). In all, 46 healthy controls had PET (11)C-AMT scans and were genotyped for 11 single-nucleotide polymorphisms (SNPs) distributed across the TPH(2) gene and its 5' upstream region. Several TPH(2) SNPs were associated with lower normalized blood-to-brain clearance of (11)C-AMT in the OBFC. Dose-effect relationships were found for two variants (rs6582071 and rs4641527, respectively, located in the 5' upstream region and intron 1) that have previously been associated with suicide. Associations in the OBFC remained statistically significant in a mixed larger sample of patients and controls. These results suggest that in humans, genetic factors might partly account for variations in serotonin synthesis in the OBFC.

Patterns of gene expression in the limbic system of suicides with and without major depression

The limbic system has consistently been associated with the control of emotions and with mood disorders. The goal of this study was to identify new molecular targets associated with suicide and with major depression using oligonucleotide microarrays in the limbic system (amygdala, hippocampus, anterior cingulate gryus (BA24) and posterior cingulate gyrus (BA29)). A total of 39 subjects were included in this study. They were all male subjects and comprised 26 suicides (depressed suicides=18, non depressed suicides=8) and 13 matched controls. Brain gene expression analysis was carried out on human brain samples using the Affymetrix HG U133 chip set. Differential expression in each of the limbic regions showed group-specific patterns of expression, supporting particular neurobiological mechanisms implicated in suicide and depression. Confirmation of genes selected based on their significance and the interest of their function with reverse transcriptase-polymerase chain reaction showed consistently correlated signals with the results obtained in the microarray analysis. Gene ontology analysis with differentially expressed genes revealed an overrepresentation of transcription and metabolism-related genes in the hippocampus and amygdala, whereas differentially expressed genes in BA24 and BA29 were more generally related to RNA-binding, regulation of enzymatic activity and protein metabolism. Limbic expression patterns were most extensively altered in the hippocampus, where processes related to major depression were associated with altered expression of factors involved with transcription and cellular metabolism. Additionally, our results confirm previous evidence pointing to global alteration of gabaergic neurotransmission in suicide and major depression, offering new avenues in the study and possibly treatment of such complex disorders. Overall, these data suggest that specific patterns of expression in the limbic system contribute to the etiology of depression and suicidal behaviors and highlight the role of the hippocampus in major depression.

Acute prefrontal cortex TMS in healthy volunteers: Effects on brain 11C-αMtrp trapping

High-frequency repetitive transcranial magnetic stimulation (rTMS) of the left dorsolateral prefrontal cortex (LDLPFC) is a technique with purported efficacy as a treatment for major depression. Here, we assessed in vivo, in healthy volunteers, the effect of acute rTMS of the LDLPFC, relative to the stimulation of the left occipital cortex (LOC), on brain regional serotonin synthesis capacity, using the [(11)C]-alpha-methyl-tryptophan ((11)C-alphaMtrp)/PET method. Ten subjects were studied twice, once following rTMS of the LDLPFC and once following rTMS of the LOC in a randomized counterbalanced order. Three blocks of 15 trains of 10 Hz rTMS were delivered 10 min apart. Behavioural and autonomic measures were recorded before and after each rTMS session. Comparisons of TMS-related changes in regional normalized brain uptake and trapping of (11)C-alphaMtrp (K*) values were carried out using SPM99. Statistically significant regional differences were identified on the basis of an extent threshold of 50 voxels, with a peak threshold of p=0.005 uncorrected. Behavioural and autonomic measures were unaffected by rTMS. Relative to LOC stimulation, LDLPFC rTMS was associated with marked changes in normalized K* in limbic areas, with significantly lower values in the left parahippocampal gyrus (BA 28) and the right insula (BA 13), and higher values in the right cingulate gyrus (BA 31) and cuneus (BA 18). These findings indicate that acute rTMS of the LDLPFC in healthy volunteers modulates aspects of tryptophan/5-HT metabolism in limbic areas. Such adaptive changes may contribute to the mechanism of action of prefrontal rTMS in major depression.

Cortical trapping of alpha-[(11)C]methyl-l-tryptophan, an index of serotonin synthesis, is lower in females than males

One neural system that may exhibit gender differences is serotonin (5-HT), a neurotransmitter implicated in the regulation of mood, cognitive processes, and impulse-control. However, most of the available evidence of gender-related differences in this system has been indirect and at times contradictory. The objective of the present study was to follow up on preliminary evidence that there are gender differences in brain regional 5-HT synthesis, as measured by trapping of alpha-[(11)C]methyl-l-tryptophan (alpha-[(11)C]MTrp). Sixty-minute dynamic scans were performed in healthy volunteers, 28 women and 31 men. Functional images of the brain trapping constant, used as a proxy for 5-HT synthesis, which correlate in the rat brain with tryptophan's conversion into 5-HT, were transferred to the standardized 3D space. The voxel based comparison was performed by Statistical Parametric Mapping with proportional normalization. There was lower normalized alpha-[(11)C]MTrp trapping in females than males throughout much of the cerebral cortex, including the left middle frontal gyrus, the bilateral inferior frontal gyrus, the bilateral precentral gyrus, the left supramarginal gyrus, the bilateral inferior parietal lobule, the left superior temporal gyrus, the bilateral posterior cingulate gyrus, and the bilateral precuneus. There were no regions in which the normalized trapping was significantly higher in females than in males. Gender differences in sub-cortical sites were not found. Women, compared to men, may have lower rates of this tracer trapping, used as a proxy for 5-HT synthesis, throughout much of the cerebral cortex which is likely related to differences in 5-HT synthesis because relative differences in the normalized trapping should be the same as those in 5-HT synthesis. These differences may be related, at least in part, to previously suggested gender differences in affect, cognitive processes, and susceptibility to 5-HT-related neuropsychiatric and neurological disorders.

Risk factors for suicide completion in major depression: a case-control study of impulsive and aggressive behaviors in men

OBJECTIVE

Major depression is a major risk factor for suicide. However, not all individuals with major depression commit suicide. Impulsive and aggressive behaviors have been proposed as risk factors for suicide, but it remains unclear whether their effect on the risk of suicide is at least partly explained by axis I disorders commonly associated with suicide, such as major depression. With a case-control design, a comparison of the level of impulsive and aggressive behaviors and the prevalence of associated psychopathology was carried out with control for the presence of primary psychopathology.

METHOD

One hundred and four male suicide completers who died during an episode of major depression and 74 living depressed male comparison subjects were investigated with proxy-based interviews by using structured diagnostic instruments and personality trait assessments.

RESULTS

The authors found that current (6-month prevalence) alcohol abuse/dependence, current drug abuse/dependence, and cluster B personality disorders increased the risk of suicide in individuals with major depression. Also, higher levels of impulsivity and aggression were associated with suicide. An analysis by age showed that these risk factors were more specific to younger suicide victims (ages 18-40). A multivariate analysis indicated that current alcohol abuse/dependence and cluster B personality disorder were two independent predictors of suicide.

CONCLUSIONS

Impulsive-aggressive personality disorders and alcohol abuse/dependence were two independent predictors of suicide in major depression, and impulsive and aggressive behaviors seem to underlie these risk factors. A developmental hypothesis of suicidal behavior, with impulsive and aggressive behaviors as the starting point, is discussed.

Increasing blood oxygen increases an index of 5-HT synthesis in human brain as measured using alpha-[(11)C]methyl-L-tryptophan and positron emission tomography

The main objective of this investigation was to test the hypothesis that brain serotonin (5-HT) synthesis, as measured by trapping of alpha-[(11)C]methyl-L-tryptophan (alpha-MTrp) using positron emission tomography (PET), can be modulated by changes in blood oxygen. The study involved six healthy participants (three male and three female), who breathed a 15% or 60% oxygen mixture starting 15 min before the injection of tracer and continuing during the entire acquisition period. Participants were injected with up to 12m Ci of alpha-MTrp. Two sets of PET images were acquired while the participants were breathing each of the oxygen mixtures and, after reconstruction, all images were converted into brain functional images illustrating the brain trapping constant K(*) (microL/g/min). The K(*) values were obtained for 12 regions of interest outlined on the magnetic resonance images. The K(*) values obtained at high and low blood oxygen content were compared by paired statistics using Tukey's post hoc correction. As there were no difference in plasma tryptophan concentrations, these K(*) values are directly related to regional 5-HT synthesis. The results showed highly significant increases (50% on average) in brain serotonin synthesis (K(*) values) at high (mean value of 223+/-41 mmHg) relative to low (mean value 77.1+/-7.7 mmHg) blood oxygen levels. This suggests that tryptophan hydroxylase is not saturated with oxygen in the living human brain and that increases in blood oxygen can elevate brain serotonin synthesis.

A systematic review of association studies investigating genes coding for serotonin receptors and the serotonin transporter: II. Suicidal behavior

The different serotonin (5-HT) receptors, including the serotonin transporter (5-HTT), are excellent candidate genes for suicide and suicidal behavior, and thus, they have been investigated in a large number of allelic association studies. The individual results of these studies have been inconsistent and definite conclusions are difficult to establish. A reliable method for assessing individual studies and generating combined results is provided by systematic reviews using meta-analytical techniques. In this study, we carried out a systematic review of studies investigating 5-HT receptors and the 5-HTT in suicidal behavior. Studies were identified by means of MEDLINE database searches and by scanning reference lists. More than 190 articles were reviewed and 26 met the inclusion criteria. In all, 14 studies investigated six different 5-HT receptor loci and 12 studies investigated the 5-HTT promoter 44 bp insertion/deletion polymorphism. Two specific meta-analyses were carried out, pooling studies investigating the 5-HT2A 102 T/C and the 5-HTT promoter loci that included, respectively, a total of 1599 and 2539 subjects. The combined evidence was significant for association with the 5-HTT locus (Mantel-Haenszel weighted odds ratio (M-H(w) OR)=1.17 CI : 1.04-1.32, P=0.009), but not for the 5-HT2A 102 T/C variant (M-H(w) OR)=1.09 CI : 0.93-1.27, P=0.319). The 5-HTT result was robust and remained significant following sensitivity analysis, suggesting that 5-HTT may play a role in the predisposition to suicide.

A systematic review of association studies investigating genes coding for serotonin receptors and the serotonin transporter: I. Affective disorders

The different 5-HT (serotonin) receptors including the serotonin transporter (5-HTT) are candidate genes for affective disorders such as major depressive disorder (MDD) and bipolar disorder (BD). They have been investigated in a number of allelic association studies where the individual results have been inconsistent, and therefore, definite conclusions are difficult to make. Systematic reviews using meta-analytical techniques are a reliable method for objectively and reproducibly assessing individual studies and generating combined result. This study aimed at reviewing published studies investigating the association between affective disorders (MDD and BD) and variation at genes coding for serotonin receptors and the serotonin transporter. We performed National Library of Medicine database searches to identify potential studies. More than 430 articles were reviewed and 86 studies met the inclusion criteria for participation in our review. Of these, 41 studies investigated 45 different 5-HT receptor variants and 45 studies investigated at least one of two commonly studied 5-HTT polymorphisms in MDD. Many studies investigated the association between MDD and BD with the 5-HT2A 102 T/C, the 5-HTT promoter 44 bp insertion/deletion and the intron 2 VNTR polymorphisms, and thus, these could be pooled using meta-analytic techniques. The overall odds ratio (OR) for the combined individual results was significant for BD and the two 5-HTT polymorphisms: Mantel-Haenszel weighted OR=1.14, CI: 1.03-1.26, P=0.015 for the promoter locus (N=3467) and Mantel-Haenszel Weighted odds ratio OR=1.18, CI: 1.05-1.32, P=0.004 for the VNTR locus (N=3620). However, sensitivity analysis indicated that, in each case, the overall positive association could be mostly attributed to the large effect of one individual study. Therefore, these results suggest that, although promising, further studies are required to assess appropriately the evidence suggesting an association between BD and 5-HTT.

Suicide and serotonin: study of variation at seven serotonin receptor genes in suicide completers

Suicide is an important public health problem, accounting for a significant proportion of total mortality among young people, particularly males. There is growing and consistent evidence suggesting that genetic factors play an important role in the predisposition to suicide. Based on several lines of evidence supporting a reduced serotonergic neurotransmission in subjects who committed suicide, we investigated variation at genes that code for serotonin receptor 1B (5-HTR1B), 1Dalpha (5-HTR1Dalpha), 1E (5-HTR1E), 1F (5-HTR1F), 2C (5-HTR2C), 5A (5-HTR5A), and 6 (5-HTR6) in a total sample of 106 suicide completers and 120 normal controls. No differences were observed in allelic or genotypic distributions between groups for any of the loci investigated. Moreover, further analysis according to suicide method or psychopathology also failed to reveal differences between groups. Our results do not support a substantial role of these serotonergic receptors in suicide completion.

Effect on mood of subthalamic DBS for Parkinson's disease: a consecutive series of 24 patients

A series of 24 consecutive PD patients were prospectively studied prior to and within 6 months postoperatively for mood, motor, and cognitive status to investigate the effects on mood of subthalamic deep brain stimulation (DBS) in PD. In six patients (25%), mood state worsened significantly, and three were transiently suicidal despite clear motor improvement. Caregivers and patients should be educated about the potential impact of this neurosurgical procedure on mood.

Amygdala-hippocampal volume and verbal memory in first-degree relatives of schizophrenic patients

Verbal memory deficits have been related to reduced volume of medial temporal structures in several neurological and psychiatric populations, including schizophrenic patients. Impairments in verbal memory have been proposed to be a marker of risk for schizophrenia. Recently, relatives of schizophrenic patients have been reported to have reduced volume of the amygdala-hippocampal complex. In this study, we evaluate the possibility that amygdala-hippocampal volume reductions may constitute one neural substrate of verbal memory deficits in first-degree relatives. Subjects were 20 healthy first-degree relatives of schizophrenic patients and 14 demographically similar controls. Verbal memory was assessed with the Logical Memory Test. Subjects were scanned with high-resolution MRI and the images were transformed into Talairach space. Volumes of interest were amygdala-anterior hippocampus and posterior hippocampus. Relatives of schizophrenic patients had intact immediate verbal memory but significantly poorer delayed verbal memory than controls. Relatives also had significantly reduced amygdala-anterior hippocampus volumes. Across all subjects, delayed verbal memory was significantly correlated with amygdala-anterior hippocampus volume. The magnitude of the correlation did not differ between the groups. These data provide an empirical link between memory performance and volumetric abnormalities in the amygdala-hippocampal complex in the relatives of schizophrenic patients.

Clinical and neurochemical effect of acute tryptophan depletion in unaffected relatives of patients with bipolar affective disorder

BACKGROUND

The lowering of mood induced by an acute tryptophan depletion (ATD) has been proposed as a candidate endophenotype for the vulnerability to manic-depressive illness. This study tests this hypothesis in relatives of probands from well-characterized multiplex families affected with bipolar affective disorder (BAD).

METHODS

In a double-blind, crossover design, 20 unaffected relatives (URs) and 19 control subjects received either a 100-g amino acid (AA) drink devoid of tryptophan or a placebo, respectively. Clinical and biochemical effects of ATD were compared between unaffected relatives of BAD probands and age- and sex-matched control subjects.

RESULTS

At 5 hours after AA drink ingestion, relative to the placebo, ATD resulted in 74% and 84% decreases in total plasma tryptophan concentrations in control subjects and relatives of patients with BAD, respectively. Unlike control subjects unaffected relatives experienced a lowering of mood during ATD but not with the placebo. Furthermore, URs tended to show increased impulsivity in the ATD condition. Measurements obtained before ingestion of the AA drink indicated that, relative to control subjects URs exhibited lower serotonin platelet concentrations, lower affinity, and fewer binding sites of the serotonin transporter for imipramine; these differences were unaffected by ATD.

CONCLUSION

These results replicate and extend previous findings suggesting that URs of patients with BAD are more susceptible to low tryptophan availability. This finding may bear significance in the purported role of serotonergic mechanisms in the vulnerability to depressive syndrome and/or illness.

[Coronary surgery of the beating heart. First year of experience in a series of 317 non-selected coronary patients]

From May 1999 to May 2000, 317 unselected patients, representing 92.7% of all coronary artery surgery procedures, underwent open heart surgery of the beating heart by median sternotomy with the aid of a cardiac stabilising device. The main preoperative characteristics were: mean age = 66.1 years; men = 78.9%; left main stem disease = 31.8%; mean left ventricular ejection fraction = 54.1%; mean Parsonnet index = 16.9. These 317 patients were compared with a group of 303 patients who underwent coronary bypass surgery the year before by the same surgical team with cardiopulmonary bypass (CPB) and cardiac standstill. Seven hundred and eighty-six distal anastomoses were carried out in the beating heart group (2.48 grafts per patient) compared with 2.91 in the CPB group: p < 0.001). There were 10.1% single bypass, 37.5% double bypass, 47.3% triple bypass and 5% quadruple bypass procedures. A cardiopulmonary bypass was required in 13 patients (4.1%). The mortality at 30 days was 3.1% versus 4.6% in the CPB group (p = NS). The need for blood transfusion was reduced by nearly 40% in the beating heart group (23.7% versus 39.9%, p < 0.001). The incidence of cerebrovascular complications was reduced from 3% in the CPB group to 0.6% in the beating heart group (p = 0.06). The peak postoperative troponine I levels were much lower in the beating heart group (2.5 versus 6.4 ng/ml, p < 0.001). The authors conclude that surgery on the beating heart is feasible in most patients. Compared with conventional surgery under CPB, there seems to be less requirement for blood transfusion and a tendency to reduce the cerebral risk. Nevertheless, a large prospective randomised trial is required to validate the potential advantages and limitations of this technique with respect to conventional surgery and to determine the optimal indications of surgery on the beating heart.

Brain Regional alpha-[11C]methyl-L-tryptophan trapping in impulsive subjects with borderline personality disorder

OBJECTIVE

Neurotransmission of serotonin (or 5-hydroxytryptamine [5-HT]) is thought to be disturbed in patients exhibiting impulsive behaviors. However, until recently it has not been possible to test this hypothesis in the brains of living humans.

METHOD

Unidirectional trapping of the 5-HT precursor analog alpha-[(11)C]methyl-L-tryptophan (alpha-[(11)C]MTrp) has been proposed as an index of 5-HT synthesis capacity. The authors measured brain regional alpha-[(11)C]MTrp trapping with positron emission tomography in medication-free subjects with borderline personality disorder (N=13) and a healthy comparison group (N=11). Impulsivity was assessed by using a laboratory measure of behavioral disinhibition, go/no-go commission errors.

RESULTS

Compared to healthy men, the men with borderline personality disorder had significantly lower alpha-[(11)C]MTrp trapping in corticostriatal sites, including the medial frontal gyrus, anterior cingulate gyrus, superior temporal gyrus, and corpus striatum. In the women with borderline personality disorder, significantly lower alpha-[(11)C]MTrp trapping was seen in fewer regions, but in both men and women, negative correlations with impulsivity scores were identified in the medial frontal gyrus, anterior cingulate gyrus, temporal gyrus, and striatum.

CONCLUSIONS

Low 5-HT synthesis capacity in corticostriatal pathways may contribute to the development of impulsive behaviors in persons with borderline personality disorder.

Depressive relapse following acute tryptophan depletion in patients with major depressive disorder

Acute tryptophan depletion (ATD) lowers serotonin synthesis and elicits depressive symptoms in some, though not all, remitted patients with major depressive disorder (MDD). In the present study, eight medication-free remitted patients with MDD, seasonal pattern, were tested twice, once following the ingestion of a tryptophan-containing mixture, once following ATD. ATD significantly increased Hamilton depression scores (p < 0.001). Four of the patients had a family history of psychiatric disorders: substance abuse (n = 4), mood disorders (n = 3) or Cluster B personality disorders (n = 3). The mood-lowering response to ATD was significantly greater in those patients with, than without, affected relatives (p < 0.001). These preliminary findings (1) support the hypothesis that depressed states are related to disturbed serotonin neurotransmission and (2) suggest that depressive symptoms following ATD might identify a subgroup of patients at high genetic risk for disorders associated with affective lability and dysregulated impulse-control, conditions thought to be related to low serotonin neurotransmission.

TPH and suicidal behavior: a study in suicide completers

An association between the gene that codes for tryptophan hydroxylase (TPH)-the rate-limiting enzyme in the synthesis of serotonin-and suicidal behavior has been investigated with some detail in samples of living subjects who attempted suicide. In this study, we investigated TPH and suicide completion, the most severe form of suicidal behavior. A relatively large sample of suicide completers (n = 101) was genotyped at three TPH loci (two polymorphisms in the promoter region, A-6526G and G-5806T, and one in intron 7, A218C) and compared to psychiatrically normal living controls (n = 129). Although no significant differences were found between groups for genetic variation at single loci, haplotype analysis revealed that one haplotype (-6526G -5806T 218C) was significantly more frequent among suicide cases than in normal controls (chi(2) = 11.30, df = 2, P = 0.0008; OR = 2.0 CI: 1.30-3.6). Further analyses suggested that this haplotype is particularly more frequent among subjects who committed suicide using violent methods. Similar results were observed in recent haplotype analyses in suicide attempters, which found that the equivalent of haplotype -6526G -5806T 218C was more frequent in impulsive attempters (Rotondo et al, Mol Psychiatry 1999; 4: 360-368). Our results replicate in suicide completers previous data observed in suicide attempters. These and other results continue to point to the substantial role that the gene that codes for TPH may play in the neurobiology of suicidal behavior.

Statistical mapping analysis of serotonin synthesis images generated in healthy volunteers using positron-emission tomography and alpha-[11C]methyl-L-tryptophan

OBJECTIVES

To assess the suitability of analyzing functional images of brain serotonin (5-HT) synthesis with statistical parametric mapping (SPM), and to investigate further possible sex-related regional differences.

DESIGN

Prospective study.

PARTICIPANTS

Six healthy men and 5 healthy women.

INTERVENTION

Participants' brains were scanned with positron-emission tomography (PET) after intravenous injection of alpha-[11C]methyl-L-tryptophan (alpha-[11C]MTrp).

OUTCOME MEASURES

Tissue radioactivity images were converted into functional images using the Patlak plot approach, and analyzed with 2 methods for global normalization in the SPM program: proportional scaling and analysis of covariance (ANCOVA).

RESULTS

The data structure suggests that PET alpha-[11C]MTrp data meet the criteria for analysis with SPM, and that the proportional scaling method is more appropriate than the ANCOVA method for normalization. Regional differences in 5-HT synthesis were identified between men and women, and the significance of these findings was supported by region of interest (ROI) analyses.

CONCLUSION

SPM analyses of PET alpha-[11C]MTrp data may be of value for identifying regional differences in brain 5-HT synthesis between groups, and in investigating the effects of psychotropic drugs. Since we found regional differences between male and female subjects, men and women should not be grouped for data analysis in PET alpha-[11C]MTrp studies.

DRD3 and DAT1 genes in schizophrenia: an association study

OBJECTIVE

To investigate the role of the dopamine receptor 3 (DRD3) and transporter 1 (DAT1) genes in schizophrenia or in modulating its phenotype.

METHODS

a Ser9Gly polymorphism in codon 9 of the DRD3 and a VNTR polymorphism in the DAT1genes were examined in two groups of schizophrenic patients, one of excellent neuroleptic responders (N=42) and one of nonresponders (N=64). A group of healthy volunteers screened for major psychiatric disorders was also included (N=89). In addition, age at onset of psychotic symptoms, attention performance and family loading for schizophrenia spectrum disorders were compared between patients with different genotypes in the DRD3 and DAT1 genes.

RESULTS

No significant differences in the allelic distribution of the DRD3 and DAT1 polymorphisms were detected between schizophrenic patients and controls. A trend toward an excess of DRD3 genotype Gly/Gly was observed in neuroleptic nonresponder schizophrenic patients compared to controls (chi(2)=3. 30, df=1, p=0.07). No significant differences in age at onset of psychotic symptoms, attention task performance or family loading for schizophrenia spectrum disorders were observed between groups with different DRD3 and DAT1 genotypes.

CONCLUSION

These results do not support the role of either of these genes in increasing susceptibility to schizophrenia or in modulating its phenotype in the studied population.

A comparison of the effects of acute tryptophan depletion and acute phenylalanine/tyrosine depletion in healthy women

Acute tryptophan depletion (ATD), which is thought to lower serotonin levels, can result in a lowering of mood. In the present study we compared the effect of ATD with acute phenylalanine/tyrosine depletion (APTD) in healthy women. Although considerable evidence relates catecholamines to the regulation of anxiety, there was no difference in anxiety responses in the ATD and APTD groups when the women underwent a mildly stressful psychological challenge. Both ATD and APTD caused a similar lowering of mood. Both depletions also increased heart rate. These results suggest that APTD is a useful method for studying the effect of low catecholamine levels in humans, and that catecholamines are involved in the regulation of mood.

Pet studies of serotonin synthesis in the human brain

The method for measuring serotonin synthesis in human brain uses [11C]alpha-methyl-L-tryptophan as a tracer and positron emission tomography. The alpha-methyl-L-tryptophan is converted to alpha-methylserotonin, which is not a substrate for monoamine oxidase and therefore accumulates in the brain. In a pilot study published recently, rates of serotonin synthesis were found to be higher in men than in women. This was due to the lower plasma free tryptophan in the women under the experimental conditions used, and does not necessarily reflect the situation in all circumstances. Acute tryptophan depletion lowered brain serotonin synthesis by 90% or more. Patients with borderline personality disorder, who exhibit emotional lability and impulsivity, may have lower brain serotonin synthesis rates than healthy controls.

Association between the methylenetetrahydrofolate reductase 677C-->T missense mutation and schizophrenia

The schizophrenia phenotype is heterogeneous with respect to clinical presentation, long-term response to medication, and outcome, possibly reflecting genetic heterogeneity and/or the presence of modifier genes. Compared to non-responders, schizophrenic patients who are responders to neuroleptic medications are characterized by a high female/male ratio, a better long-term outcome and more frequently disturbed dopamine neurotransmission. In this study, we compared two groups of schizophrenic patients selected on the basis of their long-term response to neuroleptics (excellent responders and non-responders) and a group of healthy volunteers, with regard to a missense mutation (677C-->T) in the methylenetetrahydrofolate reductase (MTHFR) gene. This polymorphism was chosen because it is functional and was previously associated with schizophrenia. The present study revealed a significant association between schizophrenia and allele T of this gene. This association was entirely due to an over-representation of allele T in responder patients compared to controls; nonresponder patients did not differ from controls. Genotype TT was more frequent in responder patients compared to controls, thus replicating the findings of Arinami et al. These results strongly suggest that the MTHFR gene is involved in the pathogenesis of schizophrenia characterized by a rapid and sustained therapeutic response to typical neuroleptics and/or a good long-term prognosis/favorable therapeutic outcome.

Functional neuroanatomy of smooth pursuit and predictive saccades

We used PET to study differences in cerebral blood flow (CBF) in smooth pursuit, predictive saccades and fixation. Eye movements were monitored in the scanner. Compared with fixation, pursuit and predictive saccades activated a network of highly similar areas, including frontal eye fields, supplementary eye fields, V5 and medial cuneus. Our findings are consistent with non-human primate studies that suggest that pursuit and saccades are controlled by similar and adjacent neural areas. Pursuit was associated with greater activation of caudate than saccades, suggesting a role for basal ganglia in pursuit that is consistent with studies of neurological populations. Saccades were associated with greater activation of cerebellum and frontal eye fields. A frontal-cerebellar loop may be important in coordinating the preparation and timing of saccades in predictive tracking.

Acute tyrosine depletion and alcohol ingestion in healthy women

BACKGROUND

Recently we reported that, in vervet monkeys, ingestion of an amino acid mixture deficient in the catecholamine precursors, phenylalanine and tyrosine, produced a decrease in alcohol self-administration. We now report the results of a similar study in humans.

METHODS

Three groups of healthy female social drinkers were administered a nutritionally balanced amino acid mixture (B, n = 13), a mixture deficient in the serotonin precursor, tryptophan (Trp-free, n = 14), or a phenylalanine/tyrosine deficient mixture (Phe/Tyr-free, n = 12). Six hours after administration of the amino acid mixture, alcohol ingestion was measured during a free-choice "Taste Test."

RESULTS

Compared to the B mixture, Phe/Tyr-free, but not Trp-free, significantly decreased the ingestion of alcohol [p < 0.02]. Neither Phe/Tyr-free nor Trp-free significantly decreased orange juice ingestion or the self-reported "Liking" of either substance. Some subjects experienced transient nausea and/or regurgitated the amino acid mixtures, but excluding these subjects did not change the results.

CONCLUSIONS

The results suggest that (a) Phe/Tyr-free may be a suitable method for investigating the role of catecholamines in the self-administration and subjective effects of alcohol, (b) acutely decreased catecholamine neurotransmission might disrupt mechanisms mediating alcohol self-administration, and (c) acutely decreased serotonin neurotransmission seems not to alter alcohol self-administration.

Effects on mood of acute phenylalanine/tyrosine depletion in healthy women

Catecholamines have been implicated in the etiology and pathophysiology of mood and anxiety disorders. In the present study, we investigated the effects of experimentally reducing catecholamine neurotransmission by means of acute phenylalanine/tyrosine depletion (APTD). Healthy female volunteers ingested: (1) a nutritionally balanced amino acid (AA) mixture (n = 14); (2) a mixture deficient in the serotonin precursor, tryptophan (n = 15); or (3) one deficient in the catecholamine precursors, phenylalanine and tyrosine (n = 12). Mood was measured at three times: at baseline and both immediately before and after an aversive psychological challenge (public speaking and mental arithmetic) conducted 5 hours after AA mixture ingestion. Acute tryptophan depletion (ATD) lowered mood and energy and increased irritability scores. These effects were statistically significant only after the psychological challenge. The effect of APTD on mood was similar to that of ATD. APTD did not attenuate the anxiety caused by the psychological challenge. These findings suggest that, in healthy women, reduced serotonin and/or catecholamine neurotransmission increases vulnerability to lowered mood, especially following exposure to aversive psychological events.

Analysis of 14 CAG repeat-containing genes in schizophrenia

Recently, it has been suggested that trinucleotide repeat-containing genes may be involved in the etiology of schizophrenia. This study was aimed at investigating putative associations between allelic variants or expansions of CAG repeat-containing genes (CAGrCG) and schizophrenia or its variability with respect to responsiveness to conventional neuroleptics. CAG repeat allelic variants of 14 expressed sequences were compared among three groups of subjects: neuroleptic-responder (R; n = 43) and neuroleptic-nonresponder (NR; n = 63) schizophrenic patients, and a control group (C; n = 122). No CAG expansions, in the range of those observed in neurodegenerative diseases, were identified in these 14 expressed sequences. The sizes of CAG repeat for the hGT1 gene were marginally different among the three groups of subjects (Kruskal-Wallis H (2, 456) = 10.48, Bonferroni corrected P = 0.047). Comparisons among the different groups indicated that neuroleptic responders have shorter alleles compared to controls (Mann-Whitney adjusted Z = -3.23, P = 0.0012). NR patients were not different from controls. These preliminary results suggest that the hGT1 gene, or a gene in its vicinity, may be involved in the etiology of schizophrenia or in modifying the disease phenotype with regard to outcome and/or neuroleptic responsiveness. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:694-699, 1999.

[Postoperative infections after heart surgery under extracorporeal circulation]

Postoperative infection is still an important cause of mortality and morbidity after cardiac surgery. The aim of this study was to assess its incidence and causes in order to optimise treatment. Between January 1996 and December 1997, 1,000 consecutive patients (253 women and 747 men) were operated for cardiac aortic pathology under cardiopulmonary bypass. The mean age was 66 +/- 11 years. The initial pathology was coronary artery disease (N = 663), valvular heart disease (N = 193), an association of the two (N = 94), thoracic aortic pathology (N = 38) or other pathologies (N = 12). The global postoperative infection rate was 4.9% (N = 49). The incidence of sternal and/or mediastinal infections was 0.7%, of bronchopneumonia 0.9%, urinary infection 2.1%, and septicaemia 1.7%. Nine patients died of the consequences of an infection. The hospital stay was significantly longer in infected patients, irrespective of the site of infection. Statistical analysis of the whole population did not show any predictive factor related to the preoperative clinical status of the patients. The only predictive factor demonstrated was the day on which surgery was performed: the infection rate in patients operated during the first 4 days of the week was 2.2% compared with 7.3% for the patients operated during the last 3 days (p = 0.004, odds ratio (OR) = 3.57). In those patients who had an urinary infection, the two identified risk factors were the female gender (p = 0.006, OR = 3.34) and an operation performed at the end of the week (p = 0.017, OR = 3.77). In patients with sternal and medistinal infections, the only identified predictive factor was combined coronary artery and valvular surgery (p = 0.009, OR = 7.43). With respect to pulmonary infections, the only predictive factor was recent preoperative myocardial infarction (< 1 month) (p = 0.004, OR = 7.5). Finally, no predictive risk factors were identified in those patients who developed septicaemia. In conclusion, this study showed that postoperative infection remains a serious complication of cardiac surgery. The prevention of these complications should be a priority for quality health care.

Neural correlates of eye tracking deficits in first-degree relatives of schizophrenic patients: a positron emission tomography study

BACKGROUND

Schizophrenia is thought to arise from the interaction of genetically mediated and environmentally triggered abnormalities in brain function. Reduced frontal activation, reported in schizophrenic patients, may be one expression of genetic risk. The present study investigated whether frontal activation in relatives of schizophrenic patients would be related to eye tracking deficits (ETD), which are considered a behavioral marker of risk for schizophrenia.

METHODS

Subjects were first-degree relatives of schizophrenic patients (n = 17) and controls (n = 11). Relatives were divided into those with normal and abnormal pursuit based on qualitative ratings. Subjects were scanned using positron emission tomography and the H(2)15O bolus subtraction technique while performing smooth pursuit and fixation. Brain areas more active in pursuit than fixation were identified in the 3 groups. Correlations were used to investigate the relationship between activation of pursuit regions and pursuit gain in the relatives.

RESULTS

Controls significantly activated frontal eye fields (FEFs) and posterior areas, including the motion processing area, V5, and cuneus. The 2 groups of relatives activated the same posterior regions as controls, but differed from each other in activation of FEFs. Relatives with normal tracking activated right dorsal FEFs while relatives with ETD did not. Individual subtractions revealed that 90% of controls and 100% of the relatives with normal tracking activated FEFs during pursuit compared with 42% of relatives with ETD (P = .009). Pursuit gain was significantly and selectively associated with percent activation of right dorsal FEFs (r = 0.74).

CONCLUSIONS

Subtle frontal dysfunction seems to be a pathophysiological substrate of ETD in relatives of schizophrenic patients, and may be one aspect of genetically mediated differences in brain function relevant to schizophrenia.

Behavioral disinhibition induced by tryptophan depletion in nonalcoholic young men with multigenerational family histories of paternal alcoholism

OBJECTIVE

A deficit in serotonergic neurotransmission has been linked to impulsive behavior, as well as to disorders characterized by disinhibition. The present study tested the hypothesis that young men at high risk for alcoholism demonstrate greater behavioral disinhibition after acute dietary depletion of tryptophan, the amino acid precursor of serotonin.

METHOD

A double-blind, placebo-comparison, between-subjects study design was used. Nonalcoholic young men with a multigenerational paternal family history of alcoholism (N = 13) or with no family history of alcoholism (N = 15) in two previous generations were administered mixtures of tryptophan-deficient amino acid to achieve plasma tryptophan depletion. Comparison subjects with a multigenerational paternal family history of alcoholism (N = 1) and comparison subjects with no family history of alcoholism (N = 18) were given a balanced mixture. Five hours after this, all were tested on a modified Taylor task and a go/ no-go task measuring aggressive response and disinhibition, respectively.

RESULTS

Plasma tryptophan levels were reduced by 89% in both groups. Tryptophan depletion had no effect on aggressive response. In contrast, tryptophan-depleted individuals with a family history of alcoholism made more commission errors (responses to stimuli associated with punishment or loss of reward) than did tryptophan-depleted individuals with no family history of alcoholism and those receiving the balanced (comparison) mixture of amino acid in either group.

CONCLUSIONS

Low serotonin levels may be implicated in the high disinhibition or impulsivity observed in some individuals with a genetic vulnerability to alcohol abuse or dependence.

Prediction of level of serotonin 2A receptor binding by serotonin receptor 2A genetic variation in postmortem brain samples from subjects who did or did not commit suicide

OBJECTIVE

Postmortem studies have indicated that suicide victims have greater serotonin receptor 2A (5-HTR2A) binding in prefrontal brain regions. However, there remains some controversy regarding the biological specificity of these findings. The authors hypothesized that the variance observed in brain 5-HTR2A binding is genetically mediated, at least in part.

METHOD

Postmortem data from 56 subjects who had committed suicide and 126 normal comparison subjects were studied; brain tissue was available from 11 subjects who committed suicide and 11 comparison subjects. Homogenate binding assays were carried out with [3H]ketanserin. Variation at the 5-HTR2A gene (HTR2A) was investigated by means of two polymorphisms: T102C and A-1438G.

RESULTS

5-HTR2A binding was greater in the prefrontal cortex of the subjects who committed suicide. In addition, the findings suggest that HTR2A variation significantly affects 5-HTR2A binding. However, no interaction between suicidal behavior and this locus was observed.

CONCLUSIONS

These results confirm previous reports of greater 5-HTR2A binding in subjects who committed suicide; they also provide preliminary evidence suggesting that the number of 5-HTR2A receptors is genetically mediated.

Lack of association between the hSKCa3 channel gene CAG polymorphism and schizophrenia

Genetic anticipation, a phenomenon characterized by increased severity of symptoms and earlier age at onset of a disease in successive generations, is believed to be present in schizophrenia. In several neurodegenerative diseases showing anticipation, the mutation causing the disease is an expanded trinucleotide repeat. Therefore, genes containing trinucleotide repeats prone to expansion have become a suitable family of candidate genes in schizophrenia. A human calcium-activated potassium channel gene (hSKCa3), possibly mapping to chromosome 22q11-13, a region previously linked to schizophrenia, was recently described. This gene contains two contiguous expressed CAG repeat stretches. Recently, long allelic variants of one of these CAG repeats were found to be overrepresented in schizophrenic patients compared to normal controls. In this study we attempted to replicate this result and to study the relationship between the length of this CAG repeat on the one hand and the severity and age at onset of the disease on the other hand. No association with the disease or correlation with the severity of schizophrenia was identified. In addition, hSKCa3 was mapped to chromosome 1. Our results do not support the involvement of this particular CAG repeat-containing gene in schizophrenia.

T102C polymorphism in the 5HT2A gene and schizophrenia: relation to phenotype and drug response variability

Although genes play a major role in the etiology of schizophrenia, no major genes involved in this disease have been identified. However, several genes with small effect have been reported, though inconsistently, to increase the risk for schizophrenia. Recently, the 5HT2A 2 allele (T102C polymorphism) was reported to be over-represented in patients with schizophrenia. Other reports have found an excess of allele 2(C) only in schizophrenic patients who are resistant to clozapine, not in those who respond to clozapine. In this study, the 5HT2A receptor allele 2 frequencies were compared between 2 groups of patients with schizophrenia (39 responders and 63 nonresponders) based on long-term outcome and response to typical neuroleptics. A control group of 90 healthy volunteers screened for mental disorders was also included. Genotype 2/2 tended to be more frequent in patients with schizophrenia with poor long-term outcome and poor response to typical neuroleptics (Bonferroni corrected p = 0.09). This difference was significant in men (Bonferroni corrected p = 0.054) but not in women. In addition, the age at first contact with psychiatric care was significantly younger in the patients with schizophrenia with genotype 2/2 than in patients with genotype 1/1. These result suggest that the 5HT2A-receptor gene may play a role in a subset of schizophrenia characterized by poor long-term outcome and poor response to neuroleptics.

Polyglutamine-containing proteins in schizophrenia

Genetic anticipation, manifested by increased severity and earlier age-at-onset of the disease over successive generations, is reported in schizophrenia. The molecular basis of anticipation in several neurodegenerative diseases is unstable coding CAG repeat expansions. Anticipation was reported in schizophrenia. Recently, studies suggested that enlarged CAG/CTG repeats are over represented in schizophrenic patients compared to normal controls. Together, these observations suggest that unstable CAG repeats may play a role in the etiology of schizophrenia. The purpose of this study is to test for the presence of polyglutamine-expanded tracts, encoded by CAG repeats, in total protein extracts derived from lymphoblastoid cell lines of schizophrenic patients. Proteins from schizophrenic patients (n = 59) and normal controls (n = 73) were separated by means of SDS-polyacrylamide gel electrophoresis, wet blotted onto nitrocellulose membrane and probed with a monoclonal antibody (mab 1C2) recognizing expanded polyglutamine arrays. Three abnormal bands corresponding to protein(s) of molecular weight of approximately 50 kDa were identified in two unrelated schizophrenic patients and in a sibling of one of these patients. None of the normal controls tested positive for this abnormal band. These results suggest that expanded polyglutamine-containing proteins, though rare, may play a role in the pathogenesis of schizophrenia.

Acute tryptophan depletion in healthy young women with a family history of major affective disorder

BACKGROUND

Acute tryptophan depletion (ATD), a means of reducing brain serotonin synthesis, lowers mood in normal males with a multi-generational family history of major affective disorder (MAD) and in normal women devoid of any family history of psychiatric illness. As both a family history of MAD and female sex are factors predisposing to depression, the hypothesis that a mood lowering response to ATD may reflect a susceptibility to depression was further investigated in young women with an extensive, multi-generational family history of MAD. In addition, the temporal stability of mood change following repeated trials of ATD was also assessed in this study.

METHODS

To deplete tryptophan, a tryptophan deficient amino acid mixture was ingested on two separate occasions. The control treatment, administered on a third occasion, was a nutritionally balanced amino acid mixture containing tryptophan.

RESULTS

A marked lowering of plasma tryptophan (85-90 %) was achieved by both depletions. In comparison to the balanced condition, family history positive (FH +) women showed no lowering of mood to either the first or second ATD (N = 13) and N = 12, respectively). Mood change between the two ATD trials (N = 13) exhibited poor temporal stability.

CONCLUSIONS

These results may indicate that serotonin responsiveness is not an important characteristic of vulnerability to depression in these women. Alternately, these negative results may be due to the exclusion of a large number of FH + women who had already experienced an episode of depression, resulting in the selection of a biased FH + sample who are resistant to the mood lowering effects of ATD.

Regional cerebral metabolic asymmetries replicated in an independent group of patients with panic disorders

BACKGROUND

Abnormal left/right (L/R) hemispheric ratios of regional cerebral glucose metabolic rates (rCMRglc) (hippocampus and inferior prefrontal cortex) have been noted in unmedicated panic disorder patients.

METHODS

An independent group of panic disorder patients placed on imipramine was studied with positron-emission tomography, testing for evidence of normalization versus persistence of the abnormal rCMRglc ratios. Differences in orbital frontal rCMRglc values between the imipramine-treated and the previously reported unmedicated panic disorder patients were tested examining for evidence that the differences would resemble those noted in obsessive-compulsive disorder (OCD) patients treated with clomipramine.

RESULTS

We found the same abnormally low L/R hippocampal and posterior inferior prefrontal rCMRglc ratios in the imipramine-treated panic disorder patients. In addition, we found posterior orbital frontal rCMRglc decreases in the imipramine-treated panic disorder patients compared with the unmedicated panic disorder patients.

CONCLUSIONS

These abnormal asymmetries found in unmedicated panic disorder patients and now in imipramine-treated panic disorder patients may reflect a trait abnormality. The orbital frontal rCMRglc differences between the imipramine-treated and unmedicated patients are similar to changes noted in OCD patients treated with clomipramine and may reflect direct or indirect effects of imipramine treatment in panic disorder patients.

Validation of a less-invasive method for measurement of serotonin synthesis rate with alpha-[11C]methyl-tryptophan

We tested in normal human subjects a less invasive method to obtain plasma input function required in the calculation of the brain serotonin synthesis rate measured with positron emission tomography (PET) and alpha-[11C]methyl-tryptophan (alpha-MTrp). The synthesis rates derived with the arterial input function were compared to those derived from venous plasma and venous sinus time-radioactivity curves obtained from dynamic PET images. Dynamic PET images were obtained for the lengths up to 90 minutes after an injection of alpha-MTrp (400 to 800 MBq). Input functions were generated from both artery and vein in three subjects, and from artery only in two subjects. Net unidirectional uptake constants of alpha-MTrp (K*; mL/g/min) were calculated in several brain regions graphically using data between 20 and 60 minutes after injection with different input functions. In the five subjects with arterial sampling, we tested two methods for correcting the input functions from the venous samples: (1) normalization to the mean exposure time at 20 minutes from arterial curve; and (2) the use of the venous sinus curve for the first 20 minutes. Venous curves coincided with the arterial ones after about 20 minutes. When the venous curves were used, there was an underestimation of the area under the curves up to 20 minutes, resulting in a 5% to 30% overestimation of K* values. Combined use of the sinus curve up to 20 minutes and venous curve from 20 to 60 minutes as an input function resulted in the K* (mL/g/min) values larger by 7.1 +/- 3.8% than the K* values estimated with the arterial input function. Normalization of the venous curve to the exposure time at 20 minutes obtained from the arterial plasma curve resulted in a bias in the K* of about -0.34 +/- 3.32%. The bias from the K* values was propagated to the serotonin synthesis rates. The use of a combination of the venous blood samples and venous sinus as the input function resulted in an acceptable bias in the serotonin synthesis rates from the tissue time-radioactivity curves generated by PET.

Tryptophan depletion, executive functions, and disinhibition in aggressive, adolescent males

Low serotonin has been associated with aggressive behavior and impulsivity. Executive functions (cognitive abilities involved in the initiation/maintenance of goal attainment) have also been related to aggression. We tested whether dietary depletion of tryptophan, the amino acid precursor of serotonin, would increase disinhibition (impulsivity) in aggressive male adolescents. Cognitive-neuropsychological variables predictive of disinhibition were explored. Stable aggressive and nonaggressive adolescent men received balanced and tryptophan-depleted, amino acid mixtures separately (counterbalanced, double-blind). Commission errors on a go/no-go learning task (i.e., failures to inhibit responding to stimuli associated with punishment/nonreward) measured disinhibition. Aggressive adolescent males made more commission errors as compared to nonaggressives. Lower executive functioning was significantly related to commission errors over and above conventional memory abilities. Tryptophan depletion had no effect on commission errors in the aggressive adolescents, possibly because of a ceiling effect.

Differences between males and females in rates of serotonin synthesis in human brain

Rates of serotonin synthesis were measured in the human brain using positron emission tomography. The sensitivity of the method is indicated by the fact that measurements are possible even after a substantial lowering of synthesis induced by acute tryptophan depletion. Unlike serotonin levels in human brain, which vary greatly in different brain areas, rates of synthesis of the indolamine are rather uniform throughout the brain. The mean rate of synthesis in normal males was found to be 52% higher than in normal females; this marked difference may be a factor relevant to the lower incidence of major unipolar depression in males.

The effect of tryptophan depletion on mood in medication-free, former patients with major affective disorder

Acute tryptophan depletion (ATD) induces transient clinical relapse in medicated patients with major affective disorder. Our objective was to determine whether this effect persists once patients are euthymic and off antidepressants. Thus, we examined the effects of ATD in fully remitted, medication-free, former patients with major depression (n = 14). ATD had no significant effect on mood. These results suggest that the previous report that ATD substantially lowers mood in pharmacologically treated patients reflects a reversal of mechanisms involved in the therapeutic effects of antidepressants. Alternatively, ATD might induce clinical relapse only in subgroups that have yet to be identified.

Behavioral and neuroendocrine responses to m-chlorophenylpiperazine in subtypes of alcoholics and in healthy comparison subjects

OBJECTIVE

The purpose of this study was to explore central serotonergic functions in subgroups of alcoholics and in healthy comparison subjects.

METHOD

The mixed serotonin (5-HT) agonist/antagonist m-chlorophenylpiperazine (m-CPP) was administered to male alcoholic patients who were classified according to the criteria of von Knorring et al. as type I alcoholics (late onset) (N = 16) or type II alcoholics (early onset with antisocial traits) (N = 24) and to 22 healthy comparison subjects. Psychological, physiological, and neuroendocrine measures were obtained before and after the m-CPP infusion.

RESULTS

m-CPP elicited subtype-related differential effects among the alcoholics; the type I alcoholics reported more anger and anxiety, and the type II alcoholics reported increased euphoria and a greater likelihood of drinking. The healthy comparison subjects exhibited a greater increase in plasma ACTH response to the m-CPP infusion than the alcoholics regardless of subtype.

CONCLUSIONS

Differences in certain 5-HT receptor functions may explain some of the clinical characteristics that differentiate the type II and type I subgroups of alcoholic patients. Furthermore, alcoholics may have reduced sensitivity of 5-HT2C receptors in comparison with healthy subjects.