Characterization of D-fenfluramine-induced hypothermia: evidence for multiple sites of action

Peripherally restricted oxytocin is sufficient to reduce food intake and motivation, while CNS entry is required for locomotor and taste avoidance effects

OBJECTIVES

Oxytocin (OT) has a well-established role in reproductive behaviours; however, it recently emerged as an important regulator of energy homeostasis. In addition to central nervous system (CNS), OT is found in the plasma and OT receptors (OT-R) are found in peripheral tissues relevant to energy balance regulation. Here, we aim to determine whether peripheral OT-R activation is sufficient to alter energy intake and expenditure.

METHODS AND RESULTS

We first show that systemic OT potently reduced food intake and food-motivated behaviour for a high-fat reward in male and female rats. As it is plausible that peripherally, intraperitoneally (IP) injected OT crosses the blood-brain barrier (BBB) to produce some of the metabolic effects within the CNS, we screened, with a novel fluorescently labelled-OT (fAF546-OT, Roxy), for the presence of IP-injected Roxy in CNS tissue relevant to feeding control and compared such with BBB-impermeable fluorescent OT-B₁₂ (fCy5-OT-B_12; BRoxy). While Roxy did penetrate the CNS, BRoxy did not. To evaluate the behavioural and thermoregulatory impact of exclusive activation of peripheral OT-R, we generated a novel BBB-impermeable OT (OT-B₁₂ ), with equipotent binding at OT-R in vitro. In vivo, IP-injected OT and OT-B₁₂ were equipotent at food intake suppression in rats of both sexes, suggesting that peripheral OT acts on peripheral OT-R to reduce feeding behaviour. Importantly, OT induced a potent conditioned taste avoidance, indistinguishable from that induced by LiCl, when applied peripherally. Remarkably, and in contrast to OT, OT-B₁₂ did not induce any conditioned taste avoidance. Limiting the CNS entry of OT also resulted in a dose-dependent reduction of emesis in male shrews. While both OT and OT-B₁₂ proved to have similar effects on body temperature, only OT resulted in home-cage locomotor depression.

CONCLUSIONS

Together our data indicate that limiting systemic OT CNS penetrance preserves the anorexic effects of the peptide and reduces the clinically undesired side effects of OT: emesis, taste avoidance and locomotor depression. Thus, therapeutic targeting of peripheral OT-R may be a viable strategy to achieve appetite suppression with better patient outcomes.

S-Ketamine Mediates Its Acute and Sustained Antidepressant-Like Activity through a 5-HT1B Receptor Dependent Mechanism in a Genetic Rat Model of Depression

Rationale: The mechanisms responsible for the unique antidepressant properties of ketamine have only been partly resolved. Recent preclinical reports implicate the neurotransmitter serotonin [5-hydroxytryptamine (5-HT)] in the antidepressant-like response of ketamine, and modulation of 5-HT_1B receptors has been hypothesized to attain an important role.

Objectives: To evaluate the role of endogenous stimulation of 5-HT_1B heteroreceptors in the antidepressant-like activity of S-ketamine.

Method: Flinders sensitive line (FSL) rats, a genetic model of depression, were depleted of endogenous 5-HT by 4-chloro-DL-phenylalanine methyl ester HCl administration (pCPA; 86 mg/kg/day for 3 days). In pCPA-pretreated and control FSL rats, the acute and sustained effects of a single dose of S-ketamine (15 mg/kg) and the selective 5-HT_1B receptor agonist CP94253 (1–6 mg/kg) alone and in combination with S-ketamine were studied in the forced swim test (FST), a commonly used assay that detects antidepressant activity.

Results: pCPA pretreatment decreased cortical 5-HT levels to ∼6% but did not affect the baseline behavioral phenotype of FSL rats. S-ketamine demonstrated acute and sustained antidepressant-like activity, both of which were abolished by 5-HT depletion. Combining S-ketamine with a sub-effective dose of CP94253 (1 mg/kg) rescued S-ketamine’s acute and sustained antidepressant-like effects, when CP94253 was administered 2 h prior to the FST. Co-administration of S-ketamine and CP94253 did not affect the plasma level of either compound, suggesting that the observed behavioral interaction could not be ascribed to a kinetic drug-drug interaction.

Conclusion: 5-HT_1B receptor activation during testing appears to be critical for S-ketamine’s antidepressant-like potentials in this model.

A High-Resolution In Vivo Atlas of the Human Brain's Serotonin System

The serotonin (5-hydroxytryptamine, 5-HT) system modulates many important brain functions and is critically involved in many neuropsychiatric disorders. Here, we present a high-resolution, multidimensional, in vivo atlas of four of the human brain's 5-HT receptors (5-HT_1A, 5-HT_1B, 5-HT_2A, and 5-HT₄) and the 5-HT transporter (5-HTT). The atlas is created from molecular and structural high-resolution neuroimaging data consisting of positron emission tomography (PET) and magnetic resonance imaging (MRI) scans acquired in a total of 210 healthy individuals. Comparison of the regional PET binding measures with postmortem human brain autoradiography outcomes showed a high correlation for the five 5-HT targets and this enabled us to transform the atlas to represent protein densities (in picomoles per milliliter). We also assessed the regional association between protein concentration and mRNA expression in the human brain by comparing the 5-HT density across the atlas with data from the Allen Human Brain atlas and identified receptor- and transporter-specific associations that show the regional relation between the two measures. Together, these data provide unparalleled insight into the serotonin system of the human brain.

SIGNIFICANCE STATEMENT

We present a high-resolution positron emission tomography (PET)- and magnetic resonance imaging-based human brain atlas of important serotonin receptors and the transporter. The regional PET-derived binding measures correlate strongly with the corresponding autoradiography protein levels. The strong correlation enables the transformation of the PET-derived human brain atlas into a protein density map of the serotonin (5-hydroxytryptamine, 5-HT) system. Next, we compared the regional receptor/transporter protein densities with mRNA levels and uncovered unique associations between protein expression and density at high detail. This new in vivo neuroimaging atlas of the 5-HT system not only provides insight in the human brain's regional protein synthesis, transport, and density, but also represents a valuable source of information for the neuroscience community as a comparative instrument to assess brain disorders.

The Gut Microbiota and Autism Spectrum Disorders

Gastrointestinal (GI) symptoms are a common comorbidity in patients with autism spectrum disorder (ASD), but the underlying mechanisms are unknown. Many studies have shown alterations in the composition of the fecal flora and metabolic products of the gut microbiome in patients with ASD. The gut microbiota influences brain development and behaviors through the neuroendocrine, neuroimmune and autonomic nervous systems. In addition, an abnormal gut microbiota is associated with several diseases, such as inflammatory bowel disease (IBD), ASD and mood disorders. Here, we review the bidirectional interactions between the central nervous system and the gastrointestinal tract (brain-gut axis) and the role of the gut microbiota in the central nervous system (CNS) and ASD. Microbiome-mediated therapies might be a safe and effective treatment for ASD.

Differential interaction with the serotonin system by S-ketamine, vortioxetine, and fluoxetine in a genetic rat model of depression

RATIONALE

The mechanisms mediating ketamine's antidepressant effect have only been partly resolved. Recent preclinical reports implicate serotonin (5-hydroxytryptamine; 5-HT) in the antidepressant-like action of ketamine. Vortioxetine is a multimodal-acting antidepressant that is hypothesized to exert its therapeutic activity through 5-HT reuptake inhibition and modulation of several 5-HT receptors.

OBJECTIVES

The objective of this study was to evaluate the therapeutic-like profiles of S-ketamine, vortioxetine, and the serotonin reuptake inhibitor fluoxetine in response to manipulation of 5-HT tone.

METHOD

Flinders Sensitive Line (FSL) rats, a genetic model of depression, were depleted of 5-HT by repeated administration of 4-chloro-DL-phenylalanine methyl ester HCl (pCPA). Using pCPA-pretreated and control FSL rats, we investigated the acute and sustained effects of S-ketamine (15 mg/kg), fluoxetine (10 mg/kg), or vortioxetine (10 mg/kg) on recognition memory and depression-like behavior in the object recognition task (ORT) and forced swim test (FST), respectively.

RESULTS

The behavioral phenotype of FSL rats was unaffected by 5-HT depletion. Vortioxetine, but not fluoxetine or S-ketamine, acutely ameliorated the memory deficits of FSL rats in the ORT irrespective of 5-HT tone. No sustained effects were observed in the ORT. In the FST, all three drugs demonstrated acute antidepressant-like activity but only S-ketamine had sustained effects. Unlike vortioxetine, the antidepressant-like responses of fluoxetine and S-ketamine were abolished by 5-HT depletion.

CONCLUSIONS

These observations suggest that the acute and sustained antidepressant-like effects of S-ketamine depend on endogenous stimulation of 5-HT receptors. In contrast, the acute therapeutic-like effects of vortioxetine on memory and depression-like behavior may be mediated by direct activity at 5-HT receptors.

Investigation of the mechanisms mediating MDMA "Ecstasy"-induced increases in cerebro-cortical perfusion determined by btASL MRI

RATIONALE

Acute administration of the recreational drug of abuse 3,4-methylenedioxymethamphetamine (MDMA; Ecstasy) has previously been shown to increase cerebro-cortical perfusion as determined by bolus-tracking arterial spin labelling (btASL) MRI.

OBJECTIVES

The purpose of the current study was to assess the mechanisms mediating these changes following systemic administration of MDMA to rats.

METHODS

Pharmacological manipulation of serotonergic, dopaminergic and nitrergic transmission was carried out to determine the mechanism of action of MDMA-induced increases in cortical perfusion using btASL MRI.

RESULTS

Fenfluramine (10 mg/kg), like MDMA (20 mg/kg), increased cortical perfusion. Increased cortical perfusion was not obtained with the 5-HT2 receptor agonist 2,5-dimethoxy-4-iodophenyl-aminopropane hydrochloride (DOI) (1 mg/kg). Depletion of central 5-HT following systemic administration of the tryptophan hydroxylase inhibitor para-chlorophenylalanine (pCPA) produced effects similar to those observed with MDMA. Pre-treatment with the 5-HT receptor antagonist metergoline (4 mg/kg) or with the 5-HT reuptake inhibitor citalopram (30 mg/kg), however, failed to produce any effect alone or influence the response to MDMA. Pre-treatment with the dopamine D1 receptor antagonist SCH 23390 (1 mg/kg) failed to influence the changes in cortical perfusion obtained with MDMA. Treatment with the neuronal nitric oxide (NO) synthase inhibitor 7-nitroindazole (7-NI) (25 mg/kg) provoked no change in cerebral perfusion alone yet attenuated the MDMA-related increase in cortical perfusion.

CONCLUSIONS

Cortical 5-HT depletion is associated with increases in perfusion although this mechanism alone does not account for MDMA-related changes. A role for NO, a key regulator of cerebrovascular perfusion, is implicated in MDMA-induced increases in cortical perfusion.

Biphasic effect of melanocortin agonists on metabolic rate and body temperature

The melanocortin system regulates metabolic homeostasis and inflammation. Melanocortin agonists have contradictorily been reported to both increase and decrease metabolic rate and body temperature. We find two distinct physiologic responses occurring at similar doses. Intraperitoneal administration of the nonselective melanocortin agonist MTII causes a melanocortin-4 receptor (Mc4r)-mediated hypermetabolism/hyperthermia. This is preceded by a profound, transient hypometabolism/hypothermia that is preserved in mice lacking any one of Mc1r, Mc3r, Mc4r, or Mc5r. Three other melanocortin agonists also caused hypothermia, which is actively achieved via seeking a cool environment, vasodilation, and inhibition of brown adipose tissue thermogenesis. These results suggest that the hypometabolic/hypothermic effect of MTII is not due to a failure of thermoregulation. The hypometabolism/hypothermia was prevented by dopamine antagonists, and MTII selectively activated arcuate nucleus dopaminergic neurons, suggesting that these neurons may contribute to the hypometabolism/hypothermia. We propose that the hypometabolism/hypothermia is a regulated response, potentially beneficial during extreme physiologic stress.

Evidence for a role of transporter-mediated currents in the depletion of brain serotonin induced by serotonin transporter substrates

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.

Improved mapping and quantification of serotonin transporter availability in the human brainstem with the HRRT

PURPOSE

The serotonin system is involved in many physiological functions and clinical conditions. Serotonergic neurons originate from the raphe nuclei in the brainstem, and reliable estimates of receptor/transporter availability in the raphe in vivo are thus of interest. Though positron emission tomography (PET) can be used to quantify receptor distribution in the brain, high noise levels prevent reliable estimation of radioligand binding in small regions such as the raphe. For this purpose, parametric imaging in combination with high-resolution PET systems may provide images with reduced noise levels and sufficient contrast for reliable quantification. This study examined the potential to evaluate radioligand binding in brainstem nuclei, and assessed the effect of improved resolution on the outcome measures.

METHODS

For comparative purposes, radioligand binding was measured with an ECAT EXACT HR PET system (resolution about 4.5 mm FWHM) and a high-resolution research tomograph (HRRT) system (resolution about 1.5 mm FWHM). Six subjects were examined with both systems on the same day using the serotonin transporter radioligand [(11)C]MADAM. Parametric images of binding potential (BP (ND)) were obtained using a wavelet-aided approach. Regions of interest (ROIs) were delineated using a threshold-based semiautomatic delineation procedure for five brainstem structures. Regional BP (ND) values were estimated by applying the ROIs to the parametric images, and the percentage difference in BP (ND) between the systems was calculated.

RESULTS

Signals for [(11)C]MADAM binding were obtained for all five brainstem structures. Overall, the HRRT provided 30-40 % higher BP (ND) values than the HR (p = 0.0017), independent of thresholds used in the ROI delineation procedure.

CONCLUSION

The methodology used enabled the estimation of [(11)C]MADAM binding in the small nuclei of the brainstem. Differences in the BP (ND) values calculated using data from the two systems were mainly attributable to their differing resolutions. The estimated BP (ND) values provided lower across-subject variability than those previously obtained using compartment analysis. This procedure may therefore facilitate quantitative studies of receptor/transporter availability in the brainstem.

Mechanisms mediating the ability of caffeine to influence MDMA ('Ecstasy')-induced hyperthermia in rats

BACKGROUND AND PURPOSE

Caffeine exacerbates the hyperthermia associated with an acute exposure to 3,4 methylenedioxymethamphetamine (MDMA, 'Ecstasy') in rats. The present study investigated the mechanisms mediating this interaction.

EXPERIMENTAL APPROACH

Adult male Sprague-Dawley rats were treated with caffeine (10 mg x kg(-1); i.p.) and MDMA (15 mg x kg(-1); i.p.) alone and in combination. Core body temperatures were monitored before and after drug administration.

KEY RESULTS

Central catecholamine depletion blocked MDMA-induced hyperthermia and its exacerbation by caffeine. Caffeine provoked a hyperthermic response when the catecholamine releaser d-amphetamine (1 mg x kg(-1)) was combined with the 5-HT releaser D-fenfluramine (5 mg x kg(-1)) or the non-selective dopamine receptor agonist apomorphine (1 mg x kg(-1)) was combined with the 5-HT(2) receptor agonist DOI (2 mg x kg(-1)) but not following either agents alone. Pretreatment with the dopamine D(1) receptor antagonist Schering (SCH) 23390 (1 mg x kg(-1)), the 5-HT(2) receptor antagonist ketanserin (5 mg x kg(-1)) or alpha(1)-adreno- receptor antagonist prazosin (0.2 mg x kg(-1)) blocked MDMA-induced hyperthermia and its exacerbation by caffeine. Co-administration of a combination of MDMA with the PDE-4 inhibitor rolipram (0.025 mg x kg(-1)) and the adenosine A(1/2) receptor antagonist 9-chloro-2-(2-furanyl)-[1,2,4]triazolo[1,5-C]quinazolin-5-amine 15943 (10 mg x kg(-1)) or the A(2A) receptor antagonist SCH 58261 (2 mg x kg(-1)) but not the A(1) receptor antagonist DPCPX (10 mg x kg(-1)) exacerbated MDMA-induced hyperthermia.

CONCLUSIONS AND IMPLICATIONS

A mechanism comprising 5-HT and catecholamines is proposed to mediate MDMA-induced hyperthermia. A combination of adenosine A(2A) receptor antagonism and PDE inhibition can account for the exacerbation of MDMA-induced hyperthermia by caffeine.

The autonomic stress-induced hyperthermia response is not enhanced by several anxiogenic drugs

While anxiety models are often based on locomotor activity responses, the stress-induced hyperthermia (SIH) paradigm uses the autonomic stress response by measuring body temperature. The effects of putative anxiogenic compounds in the SIH paradigm are inconclusive in mice and have not been examined in rats. Furthermore, it has been suggested that drug-induced effects on body temperature could be dependent on locomotor activity levels. Therefore, the effects of three anxiogenic substances, yohimbine (an α(2) receptor antagonist), mCPP (a 5HT(2C) receptor agonist) and FG-7142 (a GABA(A) receptor inverse agonist acting at the benzodiazepine site) on the stress-induced body temperature and locomotor activity response were studied in rats using novel cage stress. All anxiogenic compounds resulted in hypothermia. In contrast, FG-7142 and yohimbine increased locomotor activity levels, whereas mCPP reduced locomotor activity levels. The lack of an increased body temperature response of anxiogenic compounds indicates that the anxiogenic capacity of a drug does not necessarily yield increased autonomic stress responsivity. Moreover, the present study shows that a drug-induced decreased body temperature can be accompanied by increased locomotor activity, suggesting that both parameters represent independent parameters of the stress response.

Blockade of dopamine, but not noradrenaline, transporters produces hyperthermia in rats that lack serotonin transporters

To investigate whether life-long disturbed serotonin neurotransmission may result in adaptive changes of dopaminergic and noradrenergic systems, effects of drugs on stress-induced hyperthermia were studied in serotonin transporter knockout rats. The noradrenalin transporter blocker atomoxetine was more effective in reducing stress-induced hyperthermia, induced by an injection, in serotonin transporter (SERT) knockout (SERT(-/-)) rats compared to SERT(+/+) rats. The dopamine transporter blocker GBR12909 increased the core body temperature in SERT(-/-) rats, and had no effect on the SERT(+/+) rats. Finally, the noradrenalin transporter together with dopamine transporter blocker bupropion was more effective in decreasing the stress of an injection in SERT(-/-) rats than in SERT(+/+) rats. These data suggest that the sensitivity of dopamine and noradrenalin receptors is changed in serotonin transporter knockout rats. The lack of the serotonin transporter in SERT(-/-) rats might reflect humans with a life-long disturbed serotonin system, making this rat a good model to study possible changes in dopaminergic and noradrenergic systems in psychiatric disorders.

Determining the subjective and physiological effects of BZP on human females

BACKGROUND

"Party pills" containing benzylpiperazine (BZP) used to be widely and legally available as recreational drugs in New Zealand. There are only two published trials on human subjects (1973), which suggested that 100 mg of BZP produced subjective and physiological effects similar to 10 mg of dexamphetamine. The purpose of this study is to further investigate the subjective and physiological responses to BZP in females.

METHODS/STUDY DESIGN

In a randomised, double blind, placebo-controlled study, the subjective and physiological effects of BZP were investigated in 27 healthy, right-handed non-smoking females (mean age 22 +/- 3 years). Two groups were tested before and approximately 120 minutes after administration of a single oral dose of either 200 mg BZP (n = 14) or placebo (n = 13). Participants were required to comment on the subjective effects of BZP using three rating scales-the Addiction Centre for Research Inventory, the Profile of Mood States and the Visual Analogue Scale. Participants' blood pressure, heart rate and temperature were also measured.

RESULTS/FINDINGS

Statistical analysis using a split-plot analysis of variance and t tests revealed that BZP significantly increases blood pressure and heart rate (p < 0.05) Likewise, the subjective reports revealed that BZP has significant stimulant effects, increases euphoria and dysphoria and increases sociability and drug liking (p < 0.05).

DISCUSSION/INTERPRETATION

Physiological and subjective data reflected a clear similarity between the effects of BZP and those of other commonly known stimulants such as amphetamine and 3,4-methylenedioxymethamphetamine.

Food restriction and streptozotocin differentially modify sensitivity to the hypothermic effects of direct- and indirect-acting serotonin receptor agonists in rats

Food restriction and experimentally-induced diabetes (streptozotocin) can modify serotonin (5-HT) neurotransmission and sensitivity to drugs acting on 5-HT systems. This study examined the effects of food restriction and streptozotocin on the hypothermic effects of the 5-HT(1A) receptor agonist (+)-8-hydroxy-2-(dipropylamino)tetralin hydrobromide (8-OH-DPAT), the 5-HT(2) receptor agonist (+/-)-2,5-dimethoxy-4-methylamphetamine hydrochloride (DOM), the 5-HT releaser fenfluramine, and the selective 5-HT reuptake inhibitor (SSRI) fluoxetine. All four drugs significantly decreased body temperature in free feeding rats. Limiting rats to 10 g/day of food for 7 days decreased body weight and sensitivity to 8-OH-DPAT induced hypothermia, without affecting sensitivity to DOM, fenfluramine, or fluoxetine induced hypothermia. Subsequently, 7 days of free feeding restored body weight and sensitivity to 8-OH-DPAT. Sensitivity to all drugs was significantly decreased 7 days after 50 mg/kg streptozotocin; subsequently, 10 days of insulin replacement restored sensitivity to all drugs. These results extend to body temperature the observation that food restriction and experimentally-induced diabetes differentially modify sensitivity to drugs acting on 5-HT systems and they further suggest that the clinical response to therapeutic drugs acting on 5-HT systems might be impacted by nutritional and insulin status.

Hindbrain cocaine- and amphetamine-regulated transcript induces hypothermia mediated by GLP-1 receptors

Cocaine- and amphetamine-regulated transcript (CART) peptides are widely distributed throughout the neuraxis, including regions associated with energy balance. CART's classification as a catabolic neuropeptide is based on its inhibitory effects on feeding, coexpression with arcuate nucleus proopiomelanocortin neurons, and on limited analysis of its energy expenditure effects. Here, we investigate whether (1) caudal brainstem delivery of CART produces energetic, cardiovascular, and glycemic effects, (2) forebrain-caudal brainstem neural communication is required for those effects, and (3) glucagon-like peptide-1 receptors (GLP-1Rs) contribute to the mediation of CART-induced effects. Core temperature (Tc), heart rate (HR), activity, and blood glucose were measured in rats injected fourth intracerebroventricularly with CART (0.1, 1.0, and 2.0 microg). Food was withheld during physiologic recording and returned for overnight measurement of intake and body weight. CART induced a long-lasting (>6 h) hypothermia: a 1.5 degrees C and 1.6 degrees C drop in Tc for the 1.0 and 2.0 microg doses. Hindbrain CART application reduced food intake and body weight and increased blood glucose levels; no change in HR or activity was observed. Supracollicular decerebration eliminated the hypothermic response observed in intact rats to hindbrain ventricular CART, suggesting that forebrain processing is required for hypothermia. Pretreatment with the GLP-1R antagonist (exendin-9-39) in control rats attenuated CART hypothermia and hypophagia, indicating that GLP-1R activation contributes to hypothermic and hypophagic effects of hindbrain CART, whereas CART-induced hyperglycemia was not altered by GLP-1R blockade. Data reveal a novel function of CART in temperature regulation and open possibilities for future studies on the clinical potential of the hypothermic effect.

Chronic intermittent cold stress and serotonin depletion induce deficits of reversal learning in an attentional set-shifting test in rats

RATIONALE

Chronic stress perturbs modulatory brain neurotransmitter systems, including serotonin (5-HT), and is a risk factor for psychiatric disorders such as depression. Deficits in cognitive flexibility, reflecting prefrontal cortical dysfunction, are prominent in such disorders. Orbitofrontal cortex (OFC) has been implicated specifically in reversal learning, a form of cognitive flexibility modulated by 5-HT.

OBJECTIVES

The objectives of the study were (1) to assess the effects of chronic intermittent cold (CIC) stress, a potent metabolic stressor, on performance of rats in an attentional set-shifting test (AST), and (2) to assess a possible role for serotonin in CIC-induced deficits and test the effects of acute serotonin reuptake blockade.

MATERIALS AND METHODS

Male Sprague-Dawley rats were exposed to CIC stress (14 days x 6 h/day at 4 degrees C) before testing on the AST. In subsequent experiments, brain 5-HT was depleted in naïve rats with para-chlorophenylalanine or 5-HT release was increased acutely in CIC-stressed rats with citalopram (5 mg/kg, s.c.) given 30 min prior to the first reversal task. Microdialysis was used to assess CIC-induced changes in 5-HT release in OFC during testing.

RESULTS

CIC-stressed rats exhibited a selective impairment on the first reversal task in the AST. 5-HT depletion induced a similarly selective deficit in reversal learning. The CIC-induced impairment in reversal learning was attenuated by acute 5-HT reuptake blockade. 5-HT release was reduced in OFC of CIC-stressed rats during behavioral testing.

CONCLUSIONS

The CIC stress-induced impairment of cognitive flexibility may involve dysregulation of 5-HT modulatory function in OFC. Such deficits may thus model relevant symptoms of neuropsychiatric disorders that respond positively to SSRI treatment.

Induction of hypothermic conditions associated with increased micronuclei formation in sigma-1 receptor knockout mice after administration of the antipsychotic compound E-5842

The antipsychotic sigma-1 (sigma(1)) receptor ligand E-5842 has been shown to increase micronucleated polychromatic erythrocyte (MNPCE) frequency in mouse bone marrow secondary to compound-induced hypothermia. Interaction with sigma(1) receptor has been considered a plausible contributing factor for E-5842-induced hypothermia, raising concern for a possible class effect of sigma receptor ligands in the mouse micronucleus (MN) test. We assessed the potential of E-5842 (200 mg/kg, oral) to produce hypothermic conditions associated with increased micronuclei formation in sigma(1) receptor knockout (sigma(1)R-KO) and wild type (WT) mice. After administration, animal's rectal temperature was recorded and peripheral blood and bone marrow samples were obtained (48 hr) and assessed for induction of micronucleated reticulocytes (MNRET) and MNPCE, respectively. E-5842 administration produced marked hypothermia both in sigma(1)R-KO and WT mice. Maximum decreases from preadministration temperature were 12.2 and 13.5 degrees C in sigma(1)R-KO and WT mice, respectively. Temperature returned to normal approximately 32 hr after administration. Bone marrow examination revealed a statistical significant increase (P < 0.05) in MNPCE frequency both in sigma(1)R-KO and WT animals. Examination of peripheral blood samples showed a slight, although nonstatistical significant, increase in MNRET frequency in sigma(1)R-KO mice. No similar effect was observed among WT animals. The results obtained after E-5842 administration to sigma(1)R-KO mice indicate that induction of hypothermic conditions associated with increased MNPCE formation is not mediated by compound interaction with sigma(1) receptor, ruling out concern for a possible class effect of similar high affinity sigma(1) receptor ligands in the mouse MN test.

3,4-Methylenedioxymethamphetamine- and 8-hydroxy-2-di-n-propylamino-tetralin-induced hypothermia: role and location of 5-hydroxytryptamine 1A receptors

The popular drug of abuse 3,4-methylenedioxymethamphetamine (MDMA) has complex interactions with thermoregulatory systems, resulting in either hyperthermia or hypothermia. MDMA induces hypothermia when given to animals housed at a low ambient temperature. In this study we report that MDMA (7.5 mg/kg i.p.) given at normal ambient temperatures of 24 to 25 degrees C caused, in conscious freely moving rats, hypothermia (mean decrease from baseline of 1.1 +/- 0.06 degrees C at 40 min). Pretreating animals with a 0.5 mg/kg i.p. dose of the 5-hydroxytryptamine 1A (5-HT(1A)) antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-2-pyridinylcyclohexanecarboxamide (WAY 100635) not only prevented MDMA-induced hypothermia, but resulted in the development of hyperthermia (mean temperature increase from baseline of 0.74 +/- 0.2 degrees C at 120 min). After treatment with WAY 100635, MDMA also elicited an enhanced tachycardia (mean increases in heart rate from baseline of 110 +/- 16 beats/min at 90 min). To identify the location of 5-HT(1A) receptors responsible for hypothermia induced by MDMA, we first investigated the role of 5-HT(1A) receptors in the rostral raphe pallidus (rRP) in decreases in temperature evoked by the known 5-HT(1A) agonist 8-hydroxy-2-di-n-propylamino-tetralin (DPAT). Microinjections of 0.5 nmol of WAY 100635 into the rRP significantly attenuated DPAT (0.2 mg/kg i.p.)-elicited hypothermia. In parallel experiments, we found that microinjections of WAY 100635 into the rRP, while significantly augmenting MDMA-mediated tachycardia, did not alter body temperature. These results demonstrate that although hypothermia mediated by both MDMA and DPAT shares a common dependence on the activation of 5-HT(1A) receptors, the location of these receptors is different for each drug.

Effects of MDMA, MDA and MDEA on blood pressure, heart rate, locomotor activity and body temperature in the rat involve alpha-adrenoceptors

The effects of injection of 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA) and N-ethyl-3,4-methylenedioxyamphetamine (MDEA) (all 20 mg kg(-1)) on blood pressure, heart rate, core body temperature and locomotor activity in conscious rats were investigated using radiotelemetry. MDMA and MDA produced a prolonged increase in both systolic and diastolic pressures, with MDA causing the most marked rise. MDEA produced a transient but nonsignificant fall in diastolic pressure. The pressor response produced by MDA was accompanied by bradycardia. All three amphetamine derivatives caused an initial hypothermic response; however, MDA also produced a subsequent hyperthermia, and the speed of recovery from hypothermia was MDA>MDMA>MDEA. The alpha2A-adrenoceptor antagonist 2-((4,5-dihydro-1H-imidazol-2-yl)methyl)-2,3-dihydro-1-methyl-1H-isoindole (BRL 44408) (1 mg kg(-1)) prolonged the hypothermic response to MDMA. Only MDA induced locomotor activity when given alone, but in the presence of BRL 44408, MDMA produced increased locomotor activity. The order of potency for producing isometric contractions of rat aorta (alpha1D) and vas deferens (alpha1A) was MDA>MDMA>MDEA, with MDEA acting as an alpha1-adrenoceptor antagonist with a pK(B) of 4.79+/-0.12 (n = 4) in aorta. The order of potency for prejunctional inhibition of stimulation-evoked contractions in rat vas deferens (alpha2A-adrenoceptor mediated) was MDA>MDMA>MDEA. Blood pressure actions of the three amphetamine derivatives may be at least partly due to alpha1-adrenoceptor agonism or antagonism. The reversal of the hypothermic actions are at least partly due to alpha2A-adrenoceptor agonism since the hypothermic response was more prolonged with MDEA which exhibits low alpha2A-adrenoceptor potency, and effects of MDMA after alpha2A-adrenoceptor antagonism were similar to those of MDEA.

GABAB1 receptor subunit isoforms exert a differential influence on baseline but not GABAB receptor agonist-induced changes in mice

GABA(B) receptor agonists produce hypothermia and motor incoordination. Two GABA(B(1)) receptor subunit isoforms exist, but because of lack of specific molecular or pharmacological tools, the relevance of these isoforms in controlling basal body temperature, locomotor activity, or in vivo responses to GABA(B) receptor agonists has been unknown. Here, we used mice deficient in the GABA(B(1a)) and GABA(B(1b)) subunit isoforms to examine the influence of these isoforms on both baseline motor behavior and body temperature and on the motor-incoordinating and hypothermic responses to the GABA(B) receptor agonists l-baclofen and gamma-hydroxybutyrate (GHB). GABA(B(1b))(-/-) mice were hyperactive in a novel environment and showed slower habituation than either GABA(B(1a))(-/-) or wild-type mice. GABA(B(1b))(-/-) mice were hyperactive throughout the circadian dark phase. Hypothermia in response to l-baclofen (6 and 12 mg/kg) or GHB (1 g/kg), baclofen-induced ataxia as determined on the fixed-speed Rotarod, and GHB-induced hypolocomotion were significantly, but for the most part similarly, attenuated in both GABA(B(1a))(-/-) and GABA(B(1b))(-/-) mice. We conclude that l-baclofen and GHB are nonselective for either GABA(B(1)) receptor isoform in terms of in vivo responses. However, GABA(B(1)) receptor isoforms have distinct and different roles in mediating locomotor behavioral responses to a novel environment. Therefore, GABA(B(1a)) and GABA(B(1b)) isoforms are functionally relevant molecular variants of the GABA(B(1)) receptor subunit, which are differentially involved in specific neurophysiological processes and behaviors.

Central serotonin depletion affects rat brain areas differently: a qualitative and quantitative comparison between different treatment schemes

Depletion of rat brain serotonin (5-hydroxytryptamin, 5-HT) has been widely used to study effects of serotonin and its interaction with other transmitter systems. Various treatment regimes for serotonin depletion have been applied, but the efficacy of these seems to vary considerably. So far, no studies have systematically examined and compared different approaches. The present work combines quantitative and qualitative measurements and compares six different treatment schemes for 5-HT depletion. Treatment outcome was evaluated by HPLC measurements of 5-HT and 5-HIAA concentrations, and by 5-HT and tyrosine hydroxylase immunocytochemistry. The schemes included repeated administration of fenfluramine (FEN) and/or p-chlorophenylalanine (pCPA). The most efficient treatment for rat brain 5-HT depletion was the combined treatment with one daily pCPA (200 mg/kg) injection for 3 days followed by one injection of d,l-FEN (20 mg/kg) on the fourth day, causing a 94.9% brain 5-HT depletion. Immunostaining revealed a distinct brain distribution of the remaining 5-HT, with an almost complete depletion of 5-HT in the cerebral cortex, hippocampus and thalamus, while a substantial amount of 5-HT still was left in the raphe nuclei, the medial forebrain bundle, and the medial eminence. FEN or pCPA treatment alone caused from 68.2 to 94.0% decrease in 5-HT levels. While the pattern of 5-HT depletion using pCPA alone was comparable to the one seen with the combined treatment, the 5-HT depletion using FEN alone showed a different pattern with 5-HT distributed in several brain regions.

3,4-N-methlenedioxymethamphetamine-induced hypophagia is maintained in 5-HT1B receptor knockout mice, but suppressed by the 5-HT2C receptor antagonist RS102221

3,4-Methylenedioxy-N-methamphetamine (MDMA or 'ecstasy') is a psychoactive substance, first described as an appetite suppressant in humans, inducing side effects and even death. MDMA increases serotonin (5-HT) levels, and 5-HT inhibits food intake, but the 5-HT receptors involved in MDMA-induced changes in feeding behavior are unknown. We examined whether a systemic MDMA injection would reduce the physiological drive to eat in starved mice and tested if the inactivation of 5-HT1B or 5-HT2C receptors could restore this response. Our results indicate that in starved mice, MDMA (10 mg/kg) provoked an initial hypophagia for 1 h (-77%) followed by a period of hyperphagia (studied between 1 and 3 h). This biphasic feeding behavior due to MDMA treatment was maintained in 5-HT1B receptor-null mice or in animals treated with the 5-HT1B/1D receptor antagonist GR127935 (3 or 10 mg/kg). In contrast, MDMA-induced hypophagia (for the first 1 h period) was suppressed when combined with the 5-HT2C receptor antagonist RS102221 (2 mg/kg). However, RS102221 did not alter MDMA-induced hyperphagia (for the 1-3 h period) but did exert a stimulant effect, when administered alone, during that period. We have previously shown that MDMA or 5-HT1A/1B receptor agonist RU24969 fails to stimulate locomotor activity in 5-HT1B receptor-null mice. Our present data indicate that the 5-HT2C receptor antagonist RS102221 suppresses MDMA-induced hyperlocomotion. These findings provide the first evidence that the inactivation of 5-HT2C receptors may reduce hypophagia and motor response to MDMA, while a genetic deficit or pharmacological inactivation of 5-HT1B receptors was insufficient to alter the feeding response to MDMA.

Differential sensitivity to the motor and hypothermic effects of the GABA B receptor agonist baclofen in various mouse strains

RATIONALE

Comparison of different mouse strains can provide valuable information about the genetic control of behavioural and molecular phenotypes. Recent evidence has demonstrated the importance of GABA B receptors in anxiety and depression. Investigation of the phamacogenetics of GABA B receptor activation may aid in the understanding of mechanisms underlying the role of GABA B in affect.

OBJECTIVES

The aim of current study was to determine the relative sensitivity of different mouse strains to GABA B receptor agonism in two models of GABA B receptor function, namely hypothermia and motor incoordination.

METHODS

Mice each from 11 strains (BALB/cByJIco, DBA/2JIco, OF1, FVB/NIco, CD1, C3H/HeOuJIco, 129/SvPasIco, NMRI, C57BL/6JIco, A/JOlaHsd and Swiss) were trained to walk on a rotarod for 300 s. On the following day, mice received 0, 3, 6 or 12 mg/kg of L: -baclofen PO. Rectal temperature and rotarod performance were measured at 0, 1, 2 and 4 h after drug application.

RESULTS

L: -Baclofen produced a significant dose-dependent hypothermia and ataxia in most, but not all, mouse strains examined. The magnitude and duration of response was influenced by strain, with mice of the 129/SvPasIco strain showing largest hypothermic response to 12 mg/kg l-baclofen and C3H/HeOuJIco the lowest, whereas the BALB/cByJIco strain demonstrated greatest ataxic response on the rotarod, and NMRI the least. Interestingly, some strains (notably C3H/HeOuJIco) had marked differential hypothermic and ataxic responses, with minimal body temperature responses to L: -baclofen but significant ataxia on the rotarod observed.

CONCLUSION

There is differential genetic control on specific GABA B receptor populations that mediate hypothermia and ataxia. Further, these studies demonstrate that background strain is an important determinant of GABA B receptor mediated responses, and that hypothermic and ataxic responses may be influenced by independent genetic loci.

Induction of micronuclei in mouse bone-marrow erythrocytes in association with hypothermia after administration of the sigma receptor ligand E-5842

Oral administration of E-5842, a new sigma1 receptor ligand being developed as an antipsychotic drug, to male mice at single doses of 50, 100, 200 and 400 mg/kg produced marked and sustained decreases in rectal temperature. Both the intensity and the duration of the hypothermic effect increased with dose. Maximum decreases from the mean pre-administration temperature (36.2 degrees C) ranged from 7.5 to 12.9 degrees C for animals receiving 50 and 400 mg/kg doses, respectively. Examination of bone-marrow smears obtained 24, 48 and 72 h after administration revealed a slight but statistically significant (p < 0.05) increase in the frequency of micronucleated polychromatic erythrocytes (MNPCE) at the 48 h sampling for animals receiving the 200 mg/kg dose. These animals showed decreases from pre-administration temperature of approximately 12 degrees C, with recovery being observed 24 h after administration. When the hypothermic effect of E-5842 administration was avoided by housing treated animals under conditions of increased environmental temperature (30 degrees C) for 24 h, MNPCE frequency reverted to vehicle control values. Further, in E-5842-treated animals with an increased MNPCE frequency there was a shift in the distribution of the relative areas of micronuclei in MNPCE towards higher values. In addition, there was a statistically significant increase (p < 0.001) in the number of relatively large micronuclei (micronucleus diameter > or = 1/4 cytoplasm diameter) similar to that produced by administration of the mitotic spindle inhibitor colchicine (1 mg/kg), suggesting disturbance of mitotic apparatus as the possible underlying mechanism. The results suggest that the slight increase in MNPCE frequency observed 48 h after administration of a 200 mg/kg dose of E-5842 is due to a hypothermic effect and not to a direct effect of E-5842 on DNA.

Fenfluramine-induced hypothermia is associated with cutaneous dilation in conscious rats

The antiobesity agent, fenfluramine, produces hypothermia in rodents by an, as yet, uncharacterized mechanism. The present study was conducted in conscious rats to determine if fenfluramine-induced hypothermia was associated with cutaneous dilation. In animals maintained at 16 degrees C, core body temperature (T(CORE)) was measured telemetrically, and tail surface temperature was monitored with thermocouples fixed to the tail (T(TAIL)). D-Fenfluramine (10 mg/kg ip) produced a rapid increase in T(TAIL) of 7.7+/-0.4 degrees C (P<.001) and a decline in T(CORE) of 4+/-0.3 degrees C (P<.001). Two findings indicate that the increase in T(TAIL) was due to the withdrawal of a sympathetic vasoconstrictor tone. First, pretreatment with the ganglionic blocker, pentolinium, prevented fenfluramine-induced changes in T(TAIL). Second, when sympathetic tone to the tail was physiologically withdrawn by increasing the environmental temperature to 28 degrees C, fenfluramine treatment produced no increase in T(TAIL). Moreover, the effects of fenfluramine on T(TAIL) and T(CORE) depended on the uptake of fenfluramine into serotonergic neurons because these effects were markedly attenuated by pretreatment with the selective serotonin re-uptake inhibitor, fluoxetine. The hypothermic effect of fenfluramine occurred despite the fact that total body oxygen consumption increased by 20%. The results suggest that heat loss due to the dilation of the cutaneous circulation contributes to fenfluramine-induced hypothermia.

GABAB Receptor Antagonist-Mediated Antidepressant-Like Behavior Is Serotonin-Dependent

There is an emerging body of data purporting a role of gamma-aminobutyric acid (GABA) in the pathophysiology of mood disorders. However, the role of metabotropic GABA(B) receptors in depression is not well defined. The modified forced swim test has recently emerged as an excellent tool to assess behaviorally the role of monoamines in antidepressant action. To assess the role of GABA(B) receptors in antidepressant-related behavior, we examined a number of selective GABA(B) receptor ligands (novel positive modulators and antagonists) on behavior in the modified forced swim test. We demonstrate that the selective GABA(B) receptor antagonists CGP56433A [[3-{1-(S)-[{3-cyclohexylmethyl)hydroxy phosphinyl}-2-(S) hydroxy propyl]amino}ethyl]benzoic acid; 1-10 mg/kg] and [3-[[1-(S)-3-dichlorophenyl)ethyl]amino]-2-(S)-hydroxy-propyl]phenylmethyl-phosphinic acid hydrochloride; 3-10 mg/kg] had a similar profile to the selective serotonin reuptake inhibitor fluoxetine; they decreased immobility and increased swimming behavior. The tricyclic antidepressant desipramine decreased immobility but increased climbing behavior. In contrast, the novel GABA(B) receptor-positive modulator GS39783 (10-40 mg/kg) did not display antidepressant-like activity in the modified forced swim test. To further assess the possible interaction between GABA(B) receptor antagonism and serotonin, rats were pretreated with the tryptophan hydroxylase inhibitor para-chlorophenylalanine. 5-Hydroxytryptamine depletion (>90%) abolished the antidepressant-like behavior of CGP56433A (10 mg/kg) by attenuating the increase in swimming. Together, these data demonstrate that GABA(B) receptor antagonists via an interaction with the serotonergic system display antidepressant-like properties and therefore represent a novel approach for the treatment of depression.

Methylenedioxymethamphetamine (MDMA, 'Ecstasy'): a stressor on the immune system

Drug abuse is a global problem of considerable concern to health. One such health concern stems from the fact that many drugs of abuse have immunosuppressive actions and consequently have the potential to increase susceptibility to infectious disease. This article is focused on the impact of the amphetamine derivative, methylenedioxymethamphetamine (MDMA; 'Ecstasy') on immunity. Research conducted over the last 5 years, in both laboratory animals and humans, has demonstrated that MDMA has immunosuppressive actions. Specifically, MDMA suppresses neutrophil phagocytosis, suppresses production of the pro-inflammatory cytokines tumour necrosis factor-alpha (TNF-alpha) and interleukin (IL)-1beta, and increases production of the endogenous immunosuppressive cytokine (IL-10), thereby promoting an immunosuppressive cytokine phenotype. MDMA also suppresses circulating lymphocyte numbers, with CD4+ T cells being particularly affected, and alters T-cell function as indicated by reduced mitogen-stimulated T-cell proliferation, and a skewing of T-cell cytokine production in a T helper 2 (Th2) direction. For the most part, the aforementioned effects of MDMA are not the result of a direct action of the drug on immune cells, but rather caused by the release of endogenous immunomodulatory substances. Consequently, the physiological mechanisms that are thought to underlie the immunosuppressive effects of MDMA will be discussed. As many of the physiological changes elicited by MDMA closely resemble those induced by acute stress, it is suggested that exposure to MDMA could be regarded as a 'chemical stressor' on the immune system. Finally, the potential of MDMA-induced immunosuppression to translate into significant health risks for abusers of the drug will be discussed.

Therapeutic and adverse actions of serotonin transporter substrates

A variety of drugs release serotonin (5-HT, 5-hydroxytryptamine) from neurons by acting as substrates for 5-HT transporter (SERT) proteins. This review summarizes the neurochemical, therapeutic, and adverse actions of substrate-type 5-HT-releasing agents. The appetite suppressant (+/-)-fenfluramine is composed of (+) and (-) isomers, which are N-de-ethylated in the liver to yield the metabolites (+)- and (-)-norfenfluramine. Fenfluramines and norfenfluramines are potent 5-HT releasers. (+/-)-3,4-Methylenedioxymethamphetamine ((+/-)-MDMA, "ecstasy") and m-chlorophenylpiperazine (mCPP) are substrate-type 5-HT releasers. Fenfluramines, (+/-)-MDMA, and mCPP release neuronal 5-HT by a common non-exocytotic diffusion-exchange mechanism involving SERTs. (+)-Norfenfluramine is a potent 5-HT(2B) and 5-HT(2C) receptor agonist. The former activity may increase the risk of valvular heart disease, whereas the latter activity is implicated in the anorexic effect of systemic fenfluramine. Appetite suppressants that increase the risk for developing primary pulmonary hypertension (PPH) are all SERT substrates, but these drugs vary considerably in their propensity to increase this risk. For example, fenfluramine and aminorex are clearly linked to the occurrence of PPH, whereas other anorectics are not. Similarly, some SERT substrates deplete brain tissue 5-HT in animals (e.g., fenfluramine), while others do not (e.g., mCPP). In addition to the established indication of obesity, 5-HT releasers may help treat psychiatric disorders, such as drug and alcohol dependence, depression, and premenstrual syndrome. Viewed collectively, we believe new medications can be developed that selectively release 5-HT without increasing the risk for adverse effects of valvular heart disease, PPH, and neurotoxicity. Such agents may be useful for treating a variety of psychiatric disorders.

Additive hypothermic effects of the 5-HT1A receptor agonist 8-OH-DPAT and the dopamine D2/3 receptor agonist 7-OH-DPAT in the rat

The objective of this study was to examine possible interactions between serotonergic and dopaminergic agents lowering core temperature via stimulation of 5-HT1A and dopamine (DA) D2 receptors, respectively. The effects of the 5-HT1A receptor agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT) and the DA D2/3 receptor agonist 7-OH-DPAT on core temperature was monitored in adult male Wistar rats, approximately 300 g body weight. The temperature probe was connected to a PC-assisted temperature instrument, and an automated printer device was activated when the temperature reading had stabilized (+/-0.1 degrees C) for 10 s. As expected, 7-OH-DPAT [0.5 and 2.0 micromol x kg(-1) subcutaneous (s.c.)] as well as 8-OH-DPAT (0.15-2.4 micromol x kg(-1) s.c.), produced a dose-dependent hypothermia. When combined, there were additive effects of the two compounds, although the effects of 7-OH-DPAT were attenuated by 8-OH-DPAT at the higher doses (0.6-2.4 micromol x kg(-1)), in all probability because of emerging DA D2 receptor blocking properties of the latter compound.

Methylenedioxymethamphetamine-induced suppression of interleukin-1beta and tumour necrosis factor-alpha is not mediated by serotonin

The purpose of the present study was to examine the role of serotonin release in methylenedioxymethamphetamine (MDMA)-induced immunosuppression in rats. We examined the effect of pretreatment with the selective serotonin reuptake inhibitor paroxetine, and the tryptophan hydroxylase inhibitor para-chlorophenylalanine on MDMA-induced suppression of interleukin-1beta and tumour necrosis factor (TNF)-alpha secretion following an in vivo lipopolysaccharide challenge. Although paroxetine blocked MDMA-induced serotonin depletion in the cortex and hypothalamus, it failed to alter the suppressive effect of MDMA on lipopolysaccharide-induced TNF-alpha secretion. Similarly, although para-chlorophenylalanine caused a 90% depletion in cortical and hypothalamic serotonin content, it failed to alter the suppressive effect of MDMA on lipopolysaccharide-induced interleukin-1beta or TNF-alpha secretion. In conclusion, although MDMA is a potent releaser of serotonin, the suppressive effects of MDMA on lipopolysaccharide-induced proinflammatory cytokine secretion cannot be attributed to its serotonin-releasing properties.