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Converging lines of behavioral, electrophysiological, and biochemical evidence suggest that 5-HT 2C receptor signaling may bidirectionally influence reward-related behavior through an interaction with the mesolimbic dopamine (DA) system. Here we directly test this hypothesis by examining how modulating 5-HT 2C receptor activity affects DA-dependent behaviors and relate these effects to changes in nucleus accumbens (NAc) DA release. In C57BL/6 mice, locomotor activity and responding for a conditioned reinforcer (CRf), a measure of incentive motivation, were examined following treatment with three 5-HT 2C receptor ligands: the agonist CP809101 (0.25-3 mg/kg), the antagonist SB242084 (0.25-1 mg/kg), or the antagonist/inverse agonist SB206553 (1-5 mg/kg). We further tested whether doses of these compounds that changed locomotor activity and responding for a CRf (1 mg/kg CP809101, 0.5 mg/kg SB242084, or 2.5 mg/kg SB206553) also altered NAc DA release using in vivo microdialysis in anesthetized mice. CP809101 reduced locomotor activity, responding for a CRf, and NAc DA release. In contrast, both SB242084 and SB206553 enhanced locomotor activity, responding for a CRf, and NAc DA release, although higher doses of SB206553 produced opposite behavioral effects. Pretreatment with the non-selective DA receptor antagonist α-flupenthixol prevented SB242084 from enhancing responding for a CRf. Thus blocking tonic 5-HT 2C receptor signaling can release serotonergic inhibition of mesolimbic DA activity and enhance reward-related behavior. The observed bidirectional effects of 5-HT 2C receptor ligands may have important implications when considering the 5-HT 2C receptor as a therapeutic target for psychiatric disorders, particularly those presenting with motivational dysfunctions.

3,4-Methylenedioxymethamphetamine (MDMA) increases sociality in humans and animals. Release of serotonin (5-HT) is thought to have an important role in the increase in social behaviors, but the mechanisms underlying these effects are poorly understood. Despite the advantages of nonhuman primate models, no studies have examined the mechanisms of the social effects of MDMA in nonhuman primates. The behavior and vocalizations of four group-housed squirrel monkeys were examined following administration of MDMA, its enantiomers, and methamphetamine. 5-HT receptor antagonists and agonists were given as drug pretreatments. Data were analyzed using linear mixed-effects models. MDMA and its enantiomers increased affiliative social behaviors and vocalizations, whereas methamphetamine had only modest effects on affiliative behaviors. Pretreatment with a 5-HT 2A receptor antagonist and a 5-HT 2C receptor agonist attenuated the MDMA-induced increase in social behaviors, while a 5-HT 1A receptor antagonist did not alter affiliative vocalizations and increased MDMA-induced social contact. Nonhuman primates show MDMA-specific increases in affiliative social behaviors following MDMA administration, in concordance with human and rodent studies. MDMA-induced increases in social behaviors are 5-HT 2A , but not 5-HT 1A , receptor dependent. Understanding the neurochemical mechanisms mediating the prosocial effects of MDMA could help in the development of novel therapeutics with the unique social effects of MDMA but fewer of its limitations.

Impulsivity is an important feature of multiple neuropsychiatric disorders, and individual variation in the degree of inherent impulsivity could play a role in the generation or exacerbation of problematic behaviors. Serotonin (5-HT) actions at the 5-HT2AR receptor (5-HT2AR) promote and 5-HT2AR antagonists suppress impulsive action (the inability to withhold premature responses; motor impulsivity) upon systemic administration or microinfusion directly into the medial prefrontal cortex (mPFC), a node in the corticostriatal circuit that is thought to play a role in the regulation of impulsive action. We hypothesized that the functional capacity of the 5-HT2AR, which is governed by its expression, localization, and protein/protein interactions (eg, postsynaptic density 95 (PSD95)), may drive the predisposition to inherent impulsive action. Stable high-impulsive (HI) and low-impulsive (LI) phenotypes were identified from an outbred rodent population with the 1-choice serial reaction time (1-CSRT) task. HI rats exhibited a greater head-twitch response following administration of the preferential 5-HT2AR agonist 2,5-dimethoxy-4-iodoamphetamine (DOI) and were more sensitive to the effects of the selective 5-HT2AR antagonist M100907 to suppress impulsive action relative to LI rats. A positive correlation was observed between levels of premature responses and 5-HT2AR binding density in frontal cortex ([(3)H]-ketanserin radioligand binding). Elevated mPFC 5-HT2AR protein expression concomitant with augmented association of the 5-HT2AR with PSD95 differentiated HI from LI rats. The observed differential sensitivity of HI and LI rats to 5-HT2AR ligands and associated distinct 5-HT2AR protein profiles provide evidence that spontaneously occurring individual differences in impulsive action reflect variation in the cortical 5-HT2AR system.

The nonmedical use of synthetic cathinones is increasing on a global scale. 4-Methyl-N-methylcathinone (mephedrone) is a popular synthetic cathinone that is now illegal in the United States and other countries. Since the legislative ban on mephedrone, a number of 'second-generation' analogs have appeared in the street drug marketplace, including 4-methyl-N-ethylcathinone (4-MEC) and 4'-methyl-α-pyrrolidinopropiophenone (4-MePPP). Here we characterized the interactions of 4-MEC and 4-MePPP with transporters for 5-HT (SERT) and dopamine (DAT) using molecular, cellular, and whole-animal methods. In vitro transporter assays revealed that 4-MEC displays unusual 'hybrid' activity as a SERT substrate (ie, 5-HT releaser) and DAT blocker, whereas 4-MePPP is a blocker at both transporters but more potent at DAT. In vivo microdialysis experiments in rat brain demonstrated that 4-MEC (1-3 mg/kg, i.v.) produced large increases in extracellular 5-HT, small increases in dopamine, and minimal motor stimulation. In contrast, 4-MePPP (1-3 mg/kg, i.v.) produced selective increases in dopamine and robust motor stimulation. Consistent with its activity as a SERT substrate, 4-MEC evoked inward current in SERT-expressing Xenopus oocytes, whereas 4-MePPP was inactive in this regard. To examine drug-transporter interactions at the molecular level, we modeled the fit of 4-MEC and 4-MePPP into the binding pockets for DAT and SERT. Subtle distinctions in ligand-transporter binding were found that account for the differential effects of 4-MEC and 4-MePPP at SERT. Collectively, our results provide key information about the pharmacology of newly emerging mephedrone analogs, and give clues to structural requirements that govern drug selectivity at DAT vs SERT.

Serotonin (5-HT) transporter (SERT) substrates like fenfluramine and 3,4-methylenedioxymethamphetamine cause long-term depletion of brain 5-HT, while certain other substrates do not. The 5-HT deficits produced by SERT substrates are dependent upon transporter proteins, but the exact mechanisms responsible are unclear. Here, we compared the pharmacology of several SERT substrates: fenfluramine, d-fenfluramine, 1-(m-chlorophenyl)piperazine (mCPP) and 1-(m-trifluoromethylphenyl)piperainze (TFMPP), to establish relationships between acute drug mechanisms and the propensity for long-term 5-HT depletions. In vivo microdialysis was carried out in rat nucleus accumbens to examine acute 5-HT release and long-term depletion in the same subjects. In vitro assays were performed to measure efflux of [(3)H]5-HT in rat brain synaptosomes and transporter-mediated ionic currents in SERT-expressing Xenopus oocytes. When administered repeatedly to rats (6 mg/kg, i.p., four doses), all drugs produce large sustained elevations in extracellular 5-HT (>5-fold) with minimal effects on dopamine. Importantly, 2 weeks after dosing, only rats exposed to fenfluramine and d-fenfluramine display depletion of brain 5-HT. All test drugs evoke fluoxetine-sensitive efflux of [(3)H]5-HT from synaptosomes, but d-fenfluramine and its bioactive metabolite d-norfenfluramine induce significantly greater SERT-mediated currents than phenylpiperazines. Our data confirm that drug-induced 5-HT release probably does not mediate 5-HT depletion. However, the magnitude of transporter-mediated inward current may be a critical factor in the cascade of events leading to 5-HT deficits. This hypothesis warrants further study, especially given the growing popularity of designer drugs that target SERT.

Polymorphisms in the gene encoding the serotonin synthesis enzyme Tph2 have been identified in mental illnesses, including bipolar disorder, major depression, autism, schizophrenia, and ADHD. Deficits in cognitive flexibility and perseverative behaviors are shared common symptoms in these disorders. However, little is known about the impact of Tph2 gene variants on cognition. Mice expressing a human TPH2 variant (Tph2-KI) were used to investigate cognitive consequences of TPH2 loss of function and pharmacological treatments. We applied a recently developed behavioral assay, the automated H-maze, to study cognitive functions in Tph2-KI mice. This assay involves the consecutive discovery of three different rules: a delayed alternation task, a non-alternation task, and a delayed reversal task. Possible contribution of locomotion, reward, and sensory perception were also investigated. The expression of loss-of-function mutant Tph2 in mice was associated with impairments in reversal learning and cognitive flexibility, accompanied by perseverative behaviors similar to those observed in human clinical studies. Pharmacological restoration of 5-HT synthesis with 5-hydroxytryptophan or treatment with the 5-HT(2C) receptor agonist CP809.101 reduced cognitive deficits in Tph2-KI mice and abolished perseveration. In contrast, treatment with the psychostimulant methylphenidate exacerbated cognitive deficits in mutant mice. Results from this study suggest a contribution of TPH2 in the regulation of cognition. Furthermore, identification of a role for a 5-HT(2) receptor agonist as a cognition-enhancing agent in mutant mice suggests a potential avenue to explore for the personalized treatment of cognitive symptoms in humans with reduced 5-HT synthesis and TPH2 polymorphisms.

Whereas the majority of cocaine users quit as they experience the negative consequences of drug use, some lose control over their drug taking and compulsively seek drugs. We report that 20% of rats compulsively seek cocaine despite intermittent negative outcomes after escalating their cocaine self-administration. This compulsive subgroup showed marked reductions in forebrain serotonin utilization; increasing serotonin transmission reduced their compulsive cocaine seeking. Depleting forebrain serotonin induced compulsive cocaine seeking in rats with a limited cocaine taking history; this was reversed by systemic treatment with a 5-hydroxytryptamine (5-HT2C) receptor agonist and mimicked by systemic treatment with a 5-HT2C receptor antagonist in intact animals. These results indicate the causal involvement of reduced serotoninergic transmission in the emergence of compulsive drug seeking after a long cocaine-taking history.

The dentate gyrus of the hippocampus has been implicated in mechanisms of action of selective serotonin reuptake inhibitors (SSRIs). We have recently demonstrated that the SSRI fluoxetine can reverse the state of maturation of the adult dentate granule cells and enhances serotonin 5-HT₄ receptor-mediated synaptic potentiation at the synapses formed by their mossy fiber axons. Here, we show that fluoxetine can induce long-lasting enhancement of dopaminergic modulation at the mossy fiber synapse. Synaptic responses arising from the mossy fiber-CA3 pyramidal cell synapse were recorded using acute mouse hippocampal slices. Dopamine potentiates mossy fiber synaptic transmission by activating D₁-like receptors. Chronic fluoxetine treatment induced a prominent increase in the magnitude of dopamine-induced synaptic potentiation, and this effect was maintained at least up to 1 month after withdrawal of fluoxetine. Quantitative autoradiography revealed that binding of the D₁-like receptor ligand [³H]SCH23390 was selectively increased in the dentate gyrus and along the mossy fiber in fluoxetine-treated mice. However, binding of the 5-HT₄ receptor ligand [³H]GR113808 was not significantly changed. These results suggest that chronic fluoxetine enhanced the dopaminergic modulation at least in part by upregulating expression of D₁-like receptors, while the enhanced serotonergic modulation may be mediated by modifications of downstream signaling pathways. These enhanced monoaminergic modulations would greatly increase excitatory drive to the hippocampal circuit through the dentate gyrus. The highly localized upregulation of D₁-like receptors further supports the importance of the dentate gyrus in the mechanism of action of SSRIs.

Neurophysiological experiments in primates, alongside neuropsychological and functional magnetic resonance investigations in humans, have significantly enhanced our understanding of the neural architecture of decision making. In this review, I consider the more limited database of experiments that have investigated how dopamine and serotonin activity influences the choices of human adults. These include those experiments that have involved the administration of drugs to healthy controls, experiments that have tested genotypic influences upon dopamine and serotonin function, and, finally, some of those experiments that have examined the effects of drugs on the decision making of clinical samples. Pharmacological experiments in humans are few in number and face considerable methodological challenges in terms of drug specificity, uncertainties about pre- vs post-synaptic modes of action, and interactions with baseline cognitive performance. However, the available data are broadly consistent with current computational models of dopamine function in decision making and highlight the dissociable roles of dopamine receptor systems in the learning about outcomes that underpins value-based decision making. Moreover, genotypic influences on (interacting) prefrontal and striatal dopamine activity are associated with changes in choice behavior that might be relevant to understanding exploratory behaviors and vulnerability to addictive disorders. Manipulations of serotonin in laboratory tests of decision making in human participants have provided less consistent results, but the information gathered to date indicates a role for serotonin in learning about bad decision outcomes, non-normative aspects of risk-seeking behavior, and social choices involving affiliation and notions of fairness. Finally, I suggest that the role played by serotonin in the regulation of cognitive biases, and representation of context in learning, point toward a role in the cortically mediated cognitive appraisal of reinforcers when selecting between actions, potentially accounting for its influence upon the processing salient aversive outcomes and social choice.

Pharmacological blockade of the anandamide-degrading enzyme, fatty acid amide hydrolase (FAAH), produces CB(1) receptor (CB(1)R)-mediated analgesic, anxiolytic-like and antidepressant-like effects in murids. Using behavioral and electrophysiological approaches, we have characterized the emotional phenotype and serotonergic (5-HT) activity of mice lacking the FAAH gene in comparison to their wild type counterparts, and their response to a challenge of the CB(1)R antagonist, rimonabant. FAAH null-mutant (FAAH(-/-)) mice exhibited reduced immobility in the forced swim and tail suspension tests, predictive of antidepressant activity, which was attenuated by rimonabant. FAAH(-/-) mice showed an increase in the duration of open arm visits in the elevated plus maze, and a decrease in thigmotaxis and an increase in exploratory rearing displayed in the open field, indicating anxiolytic-like effects that were reversed by rimonabant. Rimonabant also prolonged the initiation of feeding in the novelty-suppressed feeding test. Electrophysiological recordings revealed a marked 34.68% increase in dorsal raphe 5-HT neural firing that was reversed by rimonabant in a subset of neurons exhibiting high firing rates (33.15% mean decrease). The response of the prefrontocortical pyramidal cells to the 5-HT(2A/2C) agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane ((+/-)-DOI) revealed desensitized 5-HT(2A/2C) receptors, likely linked to the observed anxiolytic-like behaviors. The hippocampal pyramidal response to the 5-HT(1A) antagonist, WAY-100635, indicates enhanced tonus on the hippocampal 5-HT(1A) heteroreceptors, a hallmark of antidepressant-like action. Together, these results suggest that FAAH genetic deletion enhances anxiolytic-like and antidepressant-like effects, paralleled by altered 5-HT transmission and postsynaptic 5-HT(1A) and 5-HT(2A/2C) receptor function.

Blunted neurohormonal responses to serotonergic agents are found in major depression and suicidal behavior, but there have been no prospective studies of their relationship to later suicide attempt. In this study, healthy volunteers and depressed subjects were administered a fenfluramine (FEN) and placebo challenge test at baseline and then followed for 2 years. Seven subjects made suicide attempts within the follow-up period. Healthy volunteers, depressed non-attempters, depressed past suicide attempters, and depressed future attempters were compared on plasma prolactin and cortisol responses, as well as on mood (Profile of Mood States; POMS) and behavioral measures that were assessed at baseline and at the end of each challenge testing day. Both past and future attempters had lower total prolactin output (area under the curve) in response to FEN relative to non-patients. Future attempters had lower cortisol response relative to all other groups. All subject groups reported a decrease in POMS Fatigue subscale score and increase in finger tapping rate after receiving FEN. Depressed subjects reported a significant decline in POMS Total, Depression, and Tension/Anxiety scores, but future attempters' did not, showing a slight mean increase. Lower cortisol response correlated with greater suicidal ideation 3 months and 1 year post-study. Logistic regression revealed that blunting of cortisol response and worsening of mood after FEN, and younger age could be used to predict later suicide attempt in the majority of cases (4/7). Results suggest that blunted cortisol and unfavorable acute mood response to serotonergic challenge, in the context of the general activating effects of these drugs, may be a risk factor for later suicide attempt.

A challenge in drug dependence is to delineate long-term neurochemical modifications induced by drugs of abuse. Repeated d-amphetamine was recently shown to disrupt a mutual regulatory link between noradrenergic and serotonergic neurons, thus inducing long-term increased responses to d-amphetamine and para-chloroamphetamine, respectively. We show here that such a sensitization of noradrenergic and serotonergic neurons also occurs following repeated treatment with cocaine, morphine, or alcohol, three compounds belonging to main groups of addictive substances. In all cases, this sensitization is prevented by alpha 1b-adrenergic and 5-HT2A receptors blockade, indicating the critical role of these receptors on long-term effects of drugs of abuse. However, repeated treatments with two non-addictive antidepressants, venlafaxine, and clorimipramine, which nevertheless inhibit noradrenergic and serotonergic reuptake, do not induce noradrenergic and serotonergic neurons sensitization. Similarly, this sensitization does not occur following repeated treatments with a specific inhibitor of dopamine (DA) reuptake, GBR12783. Moreover, we show that the effects of SCH23390, a D1 receptor antagonist known to inhibit development of d-amphetamine behavioral sensitization, are due to its 5-HT2C receptor agonist property. SCH23390 blocks amphetamine-induced release of norepinephrine and RS102221, a 5-HT2C antagonist, can reverse this inhibition as well as inhibition of noradrenergic sensitization and development of behavioral sensitization induced by repeated d-amphetamine. We propose that noradrenergic/serotonergic uncoupling is a common neurochemical consequence of repeated consumption of drugs of abuse, unrelated with DA release. Our data also suggest that compounds able to restore the link between noradrenergic and serotonergic modulatory systems could represent important therapeutic targets for investigation.

It is well documented that N-methyl-3,4-methylenedioxyamphetamine (MDMA, ecstasy) releases brain serotonin (5-HT; 5-hydroxytryptamine), noradrenaline (NE; norepinephrine), and dopamine, but the consequent effect on brain functioning remains elusive. In this study, we characterized the effects of MDMA on electrically evoked responses in the ventral CA1 region of a rat hippocampal slice preparation. Superfusion with MDMA (10 microM, 30 min) increased the population spike amplitude (PSA) by 48.9+/-31.2% and decreased population spike latency (PSL) by 103+/-139 mus (both: mean+/-SD, n=123; p<0.0001, Wilcoxon test), without affecting field excitatory postsynaptic potential (fEPSP). This effect persisted for at least 1 h after MDMA washout; we have called this EPSP-spike potentiation (ESP) by MDMA, ESP MDMA. Antagonism of GABAergic transmission did not prevent ESP MDMA, suggesting that an increase in excitability of pyramidal cells underlies this MDMA action. Block of serotonin transporter (SERT) with citalopram or 5-HT depletion with (+/-)-p-chlorophenylalanine pretreatment partially inhibited the ESP MDMA. Block of both SERT and NE transporter prevented ESP MDMA, indicating its dependence on release of both 5-HT and NE. ESP MDMA is produced by simultaneous activation of 5-HT4 and beta1 receptors, with a predominant role of 5-HT4 receptors. Block of both 5-HT4 and beta1 receptors revealed an inhibitory component of the MDMA action mediated by 5-HT1A receptor. The concentration range of MDMA which produced ESP MDMA (1-30 microM) corresponds to that commonly reached in human plasma following the ingestion of psychoactive MDMA doses, suggesting that release of both 5-HT and NE, and consequent ESP MDMA may underlie some of the psychoactive effects of MDMA in humans.

The striatum is richly innervated by serotonergic afferents from the raphe nucleus. We explored the effects of this input on striatal cholinergic interneurons from rat brain slices, by means of both conventional intracellular and whole-cell patch-clamp recordings. Bath-applied serotonin (5-HT, 3-300 microM), induced a dose-dependent membrane depolarization and increased the rate of spiking. This effect was mimicked by the 5-HT reuptake blockers citalopram and fluvoxamine. In voltage-clamped neurons, 5-HT induced an inward current, whose reversal potential was close to the K(+) equilibrium potential. Accordingly, the involvement of K(+) channels was confirmed either by increasing extracellular K(+) concentration and by blockade of K(+) channels with barium. Single-cell reverse transcriptase-polymerase chain reaction (RT-PCR) profiling demonstrated the presence of 5-HT2C, 5-HT6, and 5-HT7 receptor mRNAs in identified cholinergic interneurons. The depolarization/inward current induced by 5-HT was partially mimicked by the 5-HT2 receptor agonist 2,5-dimethoxy-4-iodoamphetamine and antagonized by both ketanserin and the selective 5-HT2C antagonist RS102221, whereas the selective 5-HT3 and 5-HT4 receptor antagonists tropisetron and RS23597-190 had no effect. The depolarizing response to 5-HT was also reduced by the selective 5-HT6 and 5-HT7 receptor antagonists SB258585 and SB269970, respectively, and mimicked by the 5-HT7 agonist, 5-CT. Accordingly, activation of either 5-HT6 or 5-HT7 receptor induced an inward current. The 5-HT response was attenuated by U73122, blocker of phospholipase C, and by SQ22,536, an inhibitor of adenylyl cyclase. These results suggest that 5-HT released by serotonergic fibers originating in the raphe nuclei has a potent excitatory effect on striatal cholinergic interneurons.

(+) 3,4,-Methylenedioxymethamphetamine (MDMA) is an abused drug that acutely releases serotonin (5-HT) and dopamine (DA) but produces long-term damage to 5-HT terminals. MDMA-induced DA release has been shown to be dampened by 5-HT. Although stress also activates the mesolimbic DA pathway, it is unknown if chronic stress after exposure to neurotoxic doses of MDMA will augment MDMA-induced DA release in the nucleus accumbens shell (NAcc(sh)). Rats were pretreated with MDMA (10 mg/kg x 4, intraperitoneal (i.p.)). After 7 days, rats were subjected to 10 days of chronic unpredictable stress. DA release in the NAcc(sh) and 5-HT in the ventral tegmental area (VTA) were measured after a challenge injection of MDMA (5 mg/kg, i.p.). The combination of pretreatment with MDMA+stress decreased basal concentrations of 5-HT in the VTA and DA in the NAcc(sh) and enhanced MDMA-stimulated DA release in the NAcc(sh). Pretreatment with MDMA or stress alone blunted MDMA-induced 5-HT release in the VTA. The augmentation of MDMA-induced DA release in rats pretreated with MDMA+chronic stress was attenuated by perfusion of the 5-HT(1B) antagonist, GR127935 into the VTA before the MDMA challenge injection. These results suggest that prior exposure to both MDMA and stress can produce a long-term augmentation in mesolimbic DA transmission and enhanced drug abuse vulnerability that is mediated, in part, by the 5-HT(1B) receptor in the VTA.

Repeated moderate doses of methamphetamine (mAMPH) damage forebrain monoaminergic terminals and nonmonoaminergic cells in somatosensory cortex, and impair performance in a novelty preference task of object recognition (OR). This study aimed to determine whether the memory deficit seen after a neurotoxic mAMPH regimen results from damage to dopamine (DA) and/or serotonin (5-HT) terminals. Animals were given a neurotoxic regimen of mAMPH, p-chloroamphetamine (PCA, preferentially damages 5-HT terminals), d-amphetamine (d-AMPH, preferentially damages DA terminals), or saline. After 1 week, animals were trained and tested for OR memory. Rats treated with mAMPH showed no recognition memory during the short-term memory (STM) test, whereas both PCA- and d-AMPH-treated rats showed OR STM scores comparable to controls. After behavioral testing, the specificity of monoaminergic lesions was determined by postmortem [125I]RTI-55 binding to dopamine (DAT) and serotonin (SERT) transporter proteins. Tissue from a separate group of animals killed 3 days after drug treatment was processed for Fluoro-Jade (F-J) fluorescence histochemistry to detect damaged cortical neurons. mAMPH-treated rats showed reductions in striatal DAT and hippocampal (HC) and perirhinal (pRh) SERT, as well as degeneration of neurons in primary somatosensory cortex. In PCA-treated rats, HC and pRh SERT were substantially depleted, but striatal DAT and cortical neuron survival were unaffected. By contrast, d-AMPH-treated animals showed marked depletions in striatal DAT and cortical neurodegeneration, but HC and pRh SERT were unaffected. This pattern of results indicates that no single feature of mAMPH-induced neurotoxicity is sufficient to produce the OR impairments seen after mAMPH treatment.

3,4-Methylenedioxymethamphetamine (MDMA) produces acute dopamine and 5-HT release in rat brain and a hyperthermic response, which is dependent on the ambient room temperature in which the animal is housed. We examined the effect of ambient room temperature (20 and 30 degrees C) on MDMA-induced dopamine and 5-HT efflux in the striatum and shell of nucleus accumbens (NAc) of freely moving rats by using microdialysis. Locomotor activity and rectal temperature were also evaluated. In the NAc, MDMA (2.5 or 5 mg/kg, i.p.) produced a substantial increase in extracellular dopamine, which was more marked at 30 degrees C. 5-HT release was also increased by MDMA given at 30 degrees C. In contrast, MDMA-induced extracellular dopamine and 5-HT increases in the striatum were unaffected by ambient temperature. At 20 degrees C room temperature, MDMA did not modify the rectal temperature but at 30 degrees C it produced a rapid and sustained hyperthermia. MDMA at 20 degrees C room temperature produced a two-fold increase in activity compared with saline-treated controls. The MDMA-induced increase in locomotor activity was more marked at 30 degrees C due to a decrease in the activity of the saline-treated controls at this high ambient temperature. These results show that high ambient temperature enhances MDMA-induced locomotor activity and monoamine release in the shell of NAc, a region involved in the incentive motivational properties of drugs of abuse, and suggest that the rewarding effects of MDMA may be more pronounced at high ambient temperature.

Previous neuroimaging studies of major depression have not controlled for the presence of personality disorders characterized by impulsive aggressive behavior, such as borderline personality disorder (BPD). Using positron emission tomography (PET), we studied regional glucose uptake in response to fenfluramine (FEN) in depressed subjects with BPD (n=11) and depressed patients without Cluster B Axis II disorders (n=8). Subjects were scanned while medication-free after a single blind placebo administration and after FEN on a second day. Brain responses were measured by PET imaging of [18F]fluorodeoxyglucose (FDG) and serial prolactin levels. Scans were compared at a voxel level using statistical parametric mapping. Correlations of changes in relative regional cerebral uptake (rCMRglu) with clinical measures were assessed. Depressed borderline patients had greater relative activity in parietotemporal cortical regions (BA 40, BA 22, and BA 42) before and after FEN activation compared to those without BPD. They also had less relative uptake in the anterior cingulate cortex (BA 32) at baseline compared to depressed patients without BPD and FEN abolished this difference. Impulsivity was positively correlated with rCMRglu in superior and middle frontal cortex (BA 6 and 44). Hostility was positively correlated with rCMRglu in temporal cortical regions (BA 21 and 22). In conclusions, borderline pathology in the context of a Major Depressive Disorder is associated with altered activity in parietotemporal and anterior cingulate cortical regions. Controlling for the presence of BPD in future imaging studies of mood disorders may elucidate similarities and differences in regional serotonergic function in these two often comorbid disorders.

Few studies have examined the relationship between genetics, stress, and sex-linked differences in neurotransmitter systems. Examining serotonin (5-HT) receptor knockout mice on stress-induced behavioral depression, female 5-HT1B receptor knockout mice demonstrated significantly reduced immobility than either male 5-HT1B receptor knockout mice or male and female wild-type mice on the tail suspension test (TST) and forced swimming test. The behavioral phenotype was identified as likely due to a disinhibition of 5-HT release, because depletion of 5-HT with parachlorophenylalanine selectively reduced immobility of female 5-HT1B receptor knockout mice in the TST. In contrast, male and female 5-HT1A receptor knockout mice demonstrated reduced immobility compared with control mice, but the depletion of 5-HT with PCPA did not reverse the antidepressant-like phenotype. Microdialysis studies confirmed significantly higher baseline levels of hippocampal 5-HT in female, but not male, 5-HT1B receptor knockout mice. Both male and female 5-HT1B receptor knockout mice demonstrated augmented dialysate responses to fluoxetine. Also, both male and female 5-HT1B receptor knockout mice demonstrated reductions of immobility in the TST after treatment with fluoxetine. Therefore, female 5-HT1B receptor knockout mice demonstrate a sex-linked disinhibition of 5-HT release that sustained higher baseline levels of hippocampal 5-HT and behavioral vulnerability to 5-HT depletion.

Forebrain serotonergic lesions attenuate the ability of d-amphetamine to decrease impulsivity in a delay-discounting paradigm, potentially through interactions between the serotonin (5-HT) and dopamine (DA) systems. Nucleus accumbens (NAC) lesions increase impulsivity, but the extent to which accumbal DA is involved in regulating impulsive choice is unknown. In the current study, the effects of intra-accumbal infusions of 6-hydroxydopamine (6-OHDA) on impulsive choice were evaluated, in combination with d-amphetamine and serotonergic drugs, in order to investigate the importance of 5-HT : DA interactions in the control of impulsive behavior. Following training on a delay-discounting task, animals received intra-NAC 6-OHDA or sham surgery. Postoperatively, subjects received systemic injections of d-amphetamine (0, 0.3, 1.0, 1.5 mg/kg) and the 5-HT(1A) receptor agonist 8-OH-DPAT (0, 0.1, 0.3, 1.0 mg/kg). Intra-NAC 6-OHDA, which reduced local DA and NA levels by 70-75%, had no effect on delay-discounting, but transiently potentiated the d-amphetamine-induced decrease in impulsive choice. 8-OH-DPAT (1.0 mg/kg) increased impulsivity in sham-operated controls, an effect which was blocked by the 5-HT(1A) receptor antagonist WAY 100635. However, 8-OH-DPAT had no effect on impulsivity in 6-OHDA NAC lesioned rats. 8-OH-DPAT (0.3 mg/kg), which did not itself alter task performance, blocked the effect of d-amphetamine in sham-operated controls, while WAY 100635 augmented the effect of amphetamine in all subjects. In an additional experiment, intracerebroventricular administration of the selective serotonergic toxin 5,7-dihydroxytryptamine, which decreased forebrain 5-HT levels by 85-90%, did not block 8-OH-DPAT's ability to increase impulsive choice. These data suggest a significant role for 5-HT : DA interactions within the NAC in the control of impulsivity, and in the mechanism by which amphetamine decreases impulsive choice.

This series of experiments explores the interaction between corticosterone and serotonin (5-HT) in the regulation of cell proliferation in the dentate gyrus of the adult rat. Intracerebroventricular 5,7-DHT (5,7-dihydroxytryptamine) (either 200 or 300 microg) resulted in highly significant depletion of 5-HT as measured by high performance liquid chromatography in the frontal cortex but had no effect on the number of proliferating cells in the dentate gyrus by measuring 5-bromo-2'-deoxyuridine (BrdU) and Ki-67 cytochemistry. Treatment with PCPA (p-chlorophenylalanine: a tryptophan hydroxylase inhibitor: 300 mg/kg initially followed by 100 mg/kg/day) resulted in reduced proliferation as measured by Ki-67 after 3 days treatment, but not by BrdU uptake, and not after 14 days treatment by either method. In addition, injection of corticosterone (10-40 mg/kg/day) for 8 days significantly reduced proliferation in the dentate gyrus, as expected, measured by both BrdU uptake and Ki-67 immunostaining. Adrenalectomized (ADX) rats with a replacement subcutaneous pellet of corticosterone showed reduced proliferation when given additional corticosterone (10 mg/kg/day for 8 days), but this was prevented by 5-HT depletion (i.c.v. 5,7-DHT). Finally, a dose-response study showed that progressive doses of corticosterone (0-40 mg/kg/day) in ADX rats resulted in diminished suppression of proliferation in 5-HT-depleted compared with 5-HT-intact rats. These results strongly suggest that 5-HT regulates the sensitivity of proliferating cells in the dentate gyrus to corticosterone.

While an involvement of brain serotonin systems in schizophrenia has been suggested by many studies, the relative role of different serotonergic projections in the brain remains unclear. We therefore examined the effects of selective brain serotonin depletion on psychotropic drug-induced locomotor hyperactivity and prepulse inhibition, two animal models of aspects of schizophrenia. Pentobarbital-anesthetized (60 mg/kg, i.p.) male Sprague-Dawley rats were stereotaxically microinjected with 1 microl of a 5 microg/microl solution of the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) into either the dorsal or median raphe nucleus. At 2 weeks after the surgery, rats with dorsal raphe lesions did not show changes in psychotropic drug-induced locomotor hyperactivity, but displayed partial disruption of prepulse inhibition. In contrast, rats with median raphe lesions showed significant enhancement of phencyclidine-induced, but not amphetamine-induced locomotor hyperactivity and a marked disruption of prepulse inhibition. These results provide evidence for differential involvement of serotonergic projections in locomotor hyperactivity and prepulse inhibition. This study may help to explain the role of different serotonin projections in the brain in the pathophysiology of schizophrenia.

The blockade of serotonin (5-HT) and norepinephrine (NE) transporters in vitro and in vivo by the dual 5-HT/NE reuptake inhibitors duloxetine and venlafaxine was compared. Duloxetine inhibited binding to the human NE and 5-HT transporters with K(i) values of 7.5 and 0.8 nM, respectively, and with a K(i) ratio of 9. Venlafaxine inhibited binding to the human NE and 5-HT transporters with K(i) values of 2480 and 82 nM, respectively, and with a K(i) ratio of 30. Duloxetine inhibited ex vivo binding to rat 5-HT transporters and NE transporters with ED(50) values of 0.03 and 0.7 mg/kg, respectively, whereas venlafaxine had ED(50) values of 2 and 54 mg/kg, respectively. The depletion of rat brain 5-HT by p-chloramphetamine and depletion of rat hypothalamic NE by 6-hydroxydopamine was blocked by duloxetine with ED(50) values of 2.3 and 12 mg/kg, respectively. Venlafaxine had ED(50) values of 5.9 and 94 mg/kg for blocking p-chloramphetamine- and 6-hydroxydopamine-induced monoamine depletion, respectively. Thus, duloxetine more potently blocks 5-HT and NE transporters in vitro and in vivo than venlafaxine.

These experiments examined the impact of extensive depletions of forebrain 5-hydroxytryptamine (5-HT; serotonin) levels on prepulse inhibition (PPI) of the acoustic startle reflex in rats. In Experiment 1, injection of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) into the dorsal and median raphe nuclei disrupted PPI. This deficit was observed beginning 2 days after lesioning and was still apparent 8 weeks later. Basal startle reactivity was not altered. The 5-HT(1A) receptor agonist 8-OH-DPAT (0.1 mg/kg) and the dopamine receptor agonist apomorphine (1mg/kg) also disrupted PPI; the effect of 8-OH-DPAT, but not apomorphine, was potentiated in 5-HT-depleted rats. Basal startle reactivity was enhanced by 8-OH-DPAT in sham-lesioned rats but not in 5,7-DHT-lesioned rats. In Experiment 2, a second method for depleting 5-HT was used. The tryptophan hydroxylase inhibitor p-chlorophenylalanine (PCPA) also disrupted PPI without altering basal startle reactivity. Again, 8-OH-DPAT disrupted PPI in control animals; this effect was not altered in PCPA-treated rats but the increase in basal startle reactivity induced by 8-OH-DPAT was not observed in PCPA-treated rats. Taken together with the results of previous experiments involving drugs that enhance 5-HT neurotransmission it appears that both increases and decreases in 5-HT activity disrupt PPI.

MDMA (3,4-methylenedioxymethamphetamine, "Ecstasy") mainly releases serotonin and dopamine. In animals, pretreatment with 5-HT(2) antagonists has been shown to attenuate neurochemical and behavioral effects of MDMA. In humans, the role of 5-HT(2) receptors in the action of MDMA has not been studied. We investigated the effect of pretreatment with the 5-HT(2A/C) antagonist ketanserin (50 mg p.o.) on subjective responses to MDMA (1.5 mg/kg p.o.) in 14 healthy volunteers using a double-blind placebo-controlled within-subject design. Subjective effects were rated by psychometric rating scales. Physiological effects measured were blood pressure, heart rate, and body temperature. Adverse effects were assessed during the sessions, and after one and three days. Ketanserin attenuated MDMA-induced perceptual changes, emotional excitation, and acute adverse responses but had little effect on MDMA-induced positive mood, well-being, extroversion, and short-term sequelae. Body temperature was lower under MDMA plus ketanserin compared to MDMA alone. The results suggest a contributing role for 5-HT(2) receptors in the action of MDMA in humans.

[H(2)(15)O]-Positron Emission Tomography (PET) was used to examine regional cerebral blood flow (rCBF) after administration of a single oral dose of the serotonin realeaser and uptake inhibitor MDMA (1.7 mg/kg) or placebo to 16 MDMA-naïve subjects. Psychological changes were assessed by psychometric rating scales. MDMA produced distributed changes in regional blood flow including increases in ventromedial frontal and occipital cortex, inferior temporal lobe and cerebellum; and decreases in the motor and somatosensory cortex, temporal lobe including left amygdala, cingulate cortex, insula and thalamus. Concomitant with these changes, subjects experienced heightened mood, increased extroversion, slight derealization and mild perceptual alterations. MDMA also produced increases in blood pressure and several side effects such as jaw clenching, lack of appetite and difficulty concentrating. These results indicate that a distributed cluster of brain areas underlie the various effects of MDMA in humans.

The increase of extracellular 5-HT in brain terminal regions produced by the acute administration of 5-HT reuptake inhibitors (SSRI's) is hampered by the activation of somatodendritic 5-HT(1A) autoreceptors in the raphe nuclei. The present in vivo electrophysiological studies were undertaken, in the rat, to assess the effects of the coadministration of venlafaxine, a dual 5-HT/NE reuptake inhibitor, and (-)pindolol on pre- and postsynaptic 5-HT(1A) receptor function. The acute administration of venlafaxine and of the SSRI paroxetine (5 mg/kg, i.v.) induced a suppression of the firing activity of dorsal hippocampus CA(3) pyramidal neurons. This effect of venlafaxine was markedly potentiated by a pretreatment with (-)pindolol (15 mg/kg, i.p.) but not by the selective beta-adrenoceptor antagonist metoprolol (15 mg/kg, i.p.). That this effect of venlafaxine was mediated by an activation of postsynaptic 5-HT(1A) receptors was suggested by its complete reversal by the 5-HT(1A) antagonist WAY 100635 (100 microg/kg, i.v.). A short-term treatment with VLX (20 mg/kg/day x 2 days) resulted in a ca. 90% suppression of the firing activity of 5-HT neurons in the dorsal raphe nucleus. This was prevented by the coadministration of (-)pindolol (15 mg/kg/day x 2 days). Taken together, these results indicate that (-)pindolol potentiated the activation of postsynaptic 5-HT(1A) receptors resulting from 5-HT reuptake inhibition probably by blocking the somatodendritic 5-HT(1A) autoreceptor, but not its postsynaptic congener. These results support and extend previous findings providing a biological substratum for the efficacy of pindolol as an accelerating strategy in major depression.

We have investigated the effect of 5-HT2 receptor agonist or antagonist administration on postsynaptic 5-HT1A receptor sensitivity assessed by two behavioral measures, reciprocal forepaw treading or hypothermia induced by acute injection of the 5-HT1A receptor agonist 8-OH-DPAT. The effectiveness of these drug treatments to downregulate 5-HT2A receptors was confirmed by measuring the binding of [3H]-ketanserin in cortical homogenates, because all of these drug treatments have been shown to result in the downregulation of 5-HT2A receptor sites. Acute or chronic treatment of rats with the 5-HT2 receptor antagonist mianserin, or chronic administration of the 5-HT2A receptor antagonist ketanserin, did not alter 8-OH-DPAT-induced hypothermia or forepaw treading. These data indicate that downregulation of 5-HT2A receptors is not sufficient to alter these postsynaptic 5-HT1A receptor-mediated responses. Chronic treatment of rats with the 5-HT2 receptor agonist DOI, however, resulted in the attenuation of both 5-HT1A receptor-mediated responses measured in separate experimental groups. The apparent desensitization of 5-HT1A receptors following chronic DOI treatment was not accompanied by a change in either the number or affinity of 5-HT1A receptor sites as measured by the binding of [3H]-8-OH-DPAT in hippocampal homogenates. Chronic activation of 5-HT2 receptors may be one mechanism by which the sensitivity postsynaptic 5-HT1A receptors can be regulated.

In the rat dorsal hippocampus and dorsal raphe nucleus, the microiontophoretic application of ergotamine and 5-HT suppressed the firing activity of CA3 pyramidal neurons and 5-HT neurons, an effect antagonized by selective 5-HT1A receptor antagonists. Co-application of ergotamine prevented the inhibitory action of 5-HT on the firing activity of CA3 pyramidal neurons but not of 5-HT neurons, indicating that ergotamine acted as a partial 5-HT1A receptor agonist in the dorsal hippocampus and as a full agonist at 5-HT1A autoreceptors. Ergotamine decreased, in a concentration-dependent manner, the electrically evoked release of [3H]5-HT in preloaded rat and guinea pig hypothalamus slices; this effect was prevented by the nonselective 5-HT receptor antagonist methiothepin but not by the selective 5-HT1B/1D receptor antagonist GR 127935 or the alpha 2-adrenoceptor antagonist idazoxan. Although body temperature in humans remained unchanged following inhaled ergotamine, in the rat, subcutaneously injected ergotamine produced a hypothermia that was prevented by a pretreatment with the 5-HT1A/1B receptor/beta-adrenoceptor antagonist pindolol. Finally in humans, ergotamine did not alter prolactin or adrenocorticotropic hormone levels, but increased growth hormone level, which was prevented by pindolol. Cortisol level was increased in humans by ergotamine, but this enhancement was unaltered by pindolol. In conclusion, the present results suggest that ergotamine acted in the rat brain as a 5-HT1A receptor agonist and as an agonist of terminal 5-HT autoreceptor of a yet undefined subtype. In humans, ergotamine also displayed some 5-HT1A receptor activity but, probably because of lack of receptor selectivity, it did not present the same profile as other 5-HT1A receptor agonists.

3, 4-methylenedioxymethamphetamine (MDMA or Ecstasy) is a substituted amphetamine whose acute and long-term effects on the serotonin system are dependent on an interaction with the 5-HT uptake transporter (SERT). Although much of the work dedicated to the study of this compound has focused on its ability to release monoamines, this drug has many important metabolic consequences on neurons and glial cells. The identification of these physiological responses will help to bridge the gap that exists in the information between the acute and neurotoxic effects of amphetamines. Substituted amphetamines have the ability to produce a long-term translocation of protein kinase C (PKC) in vivo, and this action may be crucial to the development of serotonergic neurotoxicity. Our earlier results suggested that PKC activation occurred through pre- and postsynaptic mechanisms. Because the primary site of action of these drugs is the 5-HT transporter, we now expand on our previous results and attempt to characterize MDMA's ability to translocate PKC within cortical 5-HT nerve terminals. In synaptosomes, MDMA produced a concentration-dependent increase in membrane-bound PKC (as measured by 3H-phorbol 12, 13 dibutyrate, 3H-PDBu) bindings sites. This response was abolished by cotreatment with the specific serotonin reuptake inhibitor (SSRI), fluoxetine, but not by the 5-HT2A/2C antagonist, ketanserin. In contrast, full agonists to 5-HT1A and 5-HT2 receptors did not produce significant PKC translocation. MDMA-mediated PKC translocation also requires the presence of extracellular calcium ions. Using assay conditions where extracellular calcium was absent prevented in vitro activation of PKC by MDMA. Prolonged PKC translocation has been hypothesized to contribute to the calcium-dependent neurotoxicity produced by substituted amphetamines. In addition, many physiological processes within 5-HT nerve terminals, including 5-HT reuptake and vesicular serotonin release, are susceptible to modification by PKC-dependent protein phosphorylation. Our results suggest that prolonged activation of PKC within the 5-HT nerve terminal may contribute to lasting changes in the homeostatic function of 5-HT neurons, leading to the degeneration of specific cellular elements after repeated MDMA exposure.

This report further characterizes the intermediate metabolic effects of the psychotropic amphetamine derivative, 3,4-methylenedioxymethamphetamine (MDMA or "ecstasy"), on the activity of second messenger-dependent kinases. Previous work has demonstrated that two injections of MDMA (20 mg/kg) elicits a prolonged translocation of the calcium and phospholipid-dependent enzyme, protein kinase C (PKC) in rats. However, because MDMA has actions at the 5-HT transporter and 5-HT2A/2C receptors, our experiments were directed at uncovering which of these many sites may be involved in this second messenger dependent response. A single injection of MDMA produced a time- and dose-dependent increase in the density of cortical and hippocampal PKC (as measured by 3H-phorbol 12,13-dibutyrate (PDBu) binding sites. MDMA-mediated PKC translocation was long-lasting and remained above control (saline-treated rats) for up to 24 h after injection. This effect was mimicked by another substituted amphetamine, p-chloroamphetamine (pCA), but with a temporal-response curve that was to the left of MDMA's. However, pure uptake inhibitors like fluoxetine, cocaine, and the selective 5-HT2A/2C agonist, DOB, were unable to produce a long-lasting translocation of PKC binding sites in rat cortex. Fluoxetine, a selective serotonin uptake inhibitor (SSRI) and ketanserin a 5-HT2A antagonist, attenuated PKC translocation by MDMA with differing efficacies; however, both compounds completely prevented the loss of 5-HT uptake sties after multiple doses of MDMA. These results suggest that MDMA increases PKC translocation by two interrelated mechanisms that involve 5-HT2A/2C receptors and the 5-HT transporter. This pathway appears to include: (1) the drug binding to the 5-HT transporter, (2) the release of cytosolic 5-HT stores into the extracellular space, and (3) the activation of post-synaptic 5-HT2A/2C receptors linked to G-protein-mediated phospholipid hydrolysis.

Two different doses of d-fenfluramine HCl and d,l-fenfluramine HCl (0.5 mg/kg and 1.0 mg/kg) were administered to 11 healthy male volunteers to compare the neuroendocrine responses to these two forms of fenfluramine in human subjects. Prolactin (PRL) responses to d- and d,l-fenfluramine were significantly greater than those to placebo and were equivalent at both dose levels. Adrenocortiatrophic-releasing hormone (ACTH) and cortisol (CORT) responses to d-fenfluramine at both dose levels were also significantly greater than those to placebo. In contrast, the higher dose of d,l-fenfluramine was associated only with a significant CORT response in comparison to placebo. PRL responses to d-fenfluramine were higher than the PRL response to d,l-fenfluramine at either dose level. The PRL response to d-fenfluramine at 0.5 mg/kg was very highly correlated with the PRL responses to d,l-fenfluramine at 1.0 mg/kg (r = 0.97, n = 10). Homovanillic acid (HVA) were not altered by either d, or d,l-fenfluramine at either dose in a subsample of subjects (n = 4). ACTH/CORT responses to d- and d,l-fenfluramine were modestly intercorrelated. These data suggest that the PRL response evoked by d-fenfluramine is quantitatively very similar to that evoked by d,l-fenfluramine.

(+/-)3,4-Methylenedioxymethamphetamine (MDMA) releases dopamine and serotonin in vivo and stimulates locomotor activity. Previous work demonstrated that MDMA-stimulated dopamine release could be reduced by the selective 5-HT2A receptor antagonist [R-(+)-a- (2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4-piperidinem ethanol] (MDL 100,907). In the present study MDL 100,907 significantly reduced MDMA-stimulated locomotion without affecting basal levels of locomotion. Other agents with 5-HT2A antagonist activity (ritanserin, clozapine, MDL 28,133A, or methiothepin), as well as agents that block 5-HT1A-(propranolol), D2-(haloperidol), or D1 receptors (SCH 23390) also reduced MDMA-stimulated locomotion. Intraventricularly administered 5,7-dihydroxytryptamine decreased regional 5-HT levels and attenuated MDMA-stimulated locomotion. These data support the conclusion that serotonin released onto 5-HT2A receptors contributes to MDMA-stimulated locomotion and suggest that MDMA-stimulated locomotion may be useful as an in vivo behavioral measure of 5-HT2A antagonism. The data also support previous reports of contributions of 5-HT1A, D1 and D2 receptors to MDMA-stimulated locomotion. A preliminary time-course analysis indicating time-dependent contributions of different receptors to MDMA-stimulated locomotion suggests the potential utility of this model for characterizing potential atypical antipsychotic compounds.

d-Fenfluramine, a specific 5-HT releasing agent without the catecholamine effects of d,l-fenfluramine, was used as a neuroendocrine challenge in 19 subjects with major depression and 19 healthy controls. Patients and controls were matched for age, sex, weight, and menstrual status. 5-HT-mediated prolactin and cortisol responses were both significantly attenuated in the depressed group. Patients with a history of a suicide attempt had lower cortisol responses than those without. Peak cortisol responses were inversely related to baseline cortisol levels. There were also significant relationships between hormone responses and both age and weight. These findings replicate those of a previous study using this challenge and reiterate the role of reduced 5-HT activity in suicide. They also reinforce the need for careful matching in neuroendocrine studies.