Binge ethanol administration enhances the MDMA-induced long-term 5-HT neurotoxicity in rat brain

Rationale Ecstasy abuse commonly occurs in hot, overcrowded environments in combination with alcohol. Around 90% of ecstasy users take ethanol; over 70% of these users also often drink alcohol at hazardous levels.Objectives We wished to examine whether binge ethanol administration enhanced the long-lasting 5-HT neurotoxicity induced by 3,4-methylenedioxymethamphetamine (MDMA) in rats maintained at high ambient temperature and the role of acetaldehyde.Materials and methods Rats were treated with a 4-day ethanol regimen leading to plasma ethanol levels of around 450 mg/dl. On day 5, rats were placed at 30°C and administered MDMA (5 mg/kg). Rectal temperature and hydroxyl radical formation were measured immediately before and up to 6 h after MDMA. 5-HT concentration and 5-HT transporter density were determined 7 days later. A group of rats received cyanamide (50 mg/kg) on days 1 and 3 of the 4-day-ethanol inhalation.Results In ethanol treated rats, MDMA produced a hyperthermic response similar to that observed in controls but enhanced the loss of 5-HT concentration and 5-HT transporter density in the hippocampus. Cyanamide elevated the plasma acetaldehyde concentration fivefold to sevenfold, reduced the MDMA-induced hyperthermia and increased the neuronal damage with neurotoxicity also appearing in the cortex. MDMA increased hydroxyl radical production in the hippocampus, the effect being more marked in rats pre-exposed to ethanol.Conclusions Binge ethanol administration enhances the MDMA-induced long-term 5-HT neurotoxicity by a mechanism not related to changes in acute hyperthermia but probably involving hydroxyl radical formation. The magnitude of this effect is more pronounced after increasing plasma acetaldehyde levels by aldehyde dehydrogenase inhibition.     

Cannabinoids prevent the acute hyperthermia and partially protect against the 5-HT depleting effects of MDMA ("Ecstasy") in rats

Cannabinoid-MDMA interactions were examined in male Wistar rats. MDMA (4 x 5 mg/kg or 2 x 10 mg/kg over 4 h on each of 2 days) was administered with or without Delta 9-tetrahydrocannabinol (THC) (4 x 2.5 mg/kg), the synthetic cannabinoid receptor agonist CP 55,940 (2 x 0.1 or 0.2 mg/kg) or the cannabinoid receptor antagonist SR 141716 (2 x 5 mg/kg). Co-administered Delta 9-THC and CP 55,940 but not SR 141716 prevented MDMA-induced hyperthermia, causing a powerful hypothermia. Co-administered Delta 9-THC, CP 55,940 and SR 141716 all tended to decrease MDMA-induced hyperactivity. Co-administered Delta 9-THC provided protection against the long-term increases in anxiety seen in the emergence test, but not the social interaction test, 6 weeks after MDMA treatment. Co-administered Delta 9-THC and CP 55,940, but not SR 141716, partly prevented the long-term 5-HT and 5-HIAA depletion caused by MDMA in various brain regions. SR 141716 administered with CP 55,940 and MDMA prevented the hypothermic response to the CP 55,940/MDMA combination but did not alter the CP 55,940 attenuation of MDMA-induced 5-HT depletion. These results suggest a partial protective effect of co-administered cannabinoid receptor agonists on MDMA-induced 5-HT depletion and long-term anxiety. This action appears to operate independently of cannabinoid CB1 receptors.     

Effect of different 5-HT1A receptor antagonists in combination with paroxetine on expression of the immediate-early gene Arc in rat brain

Selective 5-HT(1A) receptor antagonists enhance the effect of selective serotonin reuptake inhibitors (SSRIs) on presynaptic 5-HT function, and have potential as antidepressant augmentation therapies. The present study tested the effect of different selective 5-HT(1A) receptor antagonists (WAY 100635, NAD-299, p-MPPI and LY 426965) in combination with a SSRI (paroxetine), on postsynaptic 5-HT function measured by increased expression of the immediate early gene, Arc.Paroxetine (5 mg/kg s.c.) combined with WAY 100635 (0.3 mg/kg s.c.) increased Arc mRNA in frontal, parietal and piriform cortices, and caudate putamen. Paroxetine (5 mg/kg s.c.) plus NAD-299 (1 or 5 mg/kg s.c.) had a similar effect. None of these drugs increased Arc mRNA when administered alone. Paroxetine (5 mg/kg s.c.) plus p-MPPI (8.5 mg/kg s.c.) also increased Arc mRNA but p-MPPI itself elevated Arc mRNA in many regions. Whilst LY 426965 (3 or 10 mg/kg s.c.) had no effect alone, when combined with paroxetine (5 mg/kg s.c.), the drug increased Arc mRNA in caudate putamen but not cortical regions.In conclusion, this study demonstrates that four 5-HT(1A) receptor antagonists augment the effect of an SSRI on Arc mRNA expression, which is suggestive of increased postsynaptic 5-HT function. However, the data reveal certain differences in the 5-HT(1A) receptor antagonists not recognised in models of presynaptic 5-HT function.     

Caffeine promotes hyperthermia and serotonergic loss following co-administration of the substituted amphetamines, MDMA ("Ecstasy") and MDA ("Love")

The present study determined the effect of caffeine co-administration on the core body temperature response and long-term serotonin (5-HT) loss induced by methylenedioxymethamphetamine (MDMA; "Ecstasy") and its metabolite methylenedioxyamphetamine (MDA; "Love") to rats. In group-housed animals, caffeine (10 mg/kg) enhanced the acute toxicity of MDMA (15 mg/kg) and MDA (7.5 mg/kg), resulting in an exaggerated hyperthermic response (+2 degrees C for 5 h following MDMA and +1.5 degrees C for 3 h following MDA) when compared to MDMA (+1 degree C for 3 h) and MDA (+1 degree C for 1 h) alone. Co-administration of caffeine with MDMA or MDA was also associated with increased lethality. To reduce the risk of lethality, doses of MDMA and MDA were reduced in further experiments and the animals were housed individually. To examine the effects of repeated administration, animals received MDMA (10 mg/kg) or MDA (5 mg/kg) with or without caffeine (10 mg/kg) twice daily for 4 consecutive days. MDMA and MDA alone induced hypothermia (fall of 1 to 2 degrees C) over the 4 treatment days. Co-administration of caffeine with MDMA or MDA resulted in hyperthermia (increase of up to 2.5 degrees C) following acute administration compared to animals treated with caffeine or MDMA/MDA alone. This hyperthermic response to caffeine and MDMA was not observed with repeated administration, unlike caffeine + MDA, where hyperthermia was obtained over the 4 day treatment period. In addition, 4 weeks after the last treatment, co-administration of caffeine with MDA (but not MDMA) induced a reduction in 5-HT and 5-hydroxyindole acetic acid (5-HIAA) concentrations in frontal cortex (to 61% and 58% of control, respectively), hippocampus (48% and 60%), striatum (79% and 64%) and amygdala (63% and 37%). However, when caffeine (10 mg/kg) and MDMA (2.5 mg/kg) were co-administered four times daily for 2 days to group-housed animals, both hyperthermia and hippocampal 5-HT loss were observed (reduced to 68% of control). Neither MDMA nor MDA alone induced a significant reduction in regional 5-HT or 5-HIAA concentrations following repeated administration. In conclusion, caffeine promotes the acute and long-term toxicity associated with MDMA and MDA. This is a serious drug interaction, which could have important acute and long-term health consequences for recreational drug users.     

Effect of ambient temperature on hyperthermia and hyperkinesis induced by 3,4-methylenedioxymethamphetamine (MDMA or “ecstasy”) in rats

A stress-free, biotelemetric monitoring technique was used to investigate the effects of ambient temperature (T _a) on the hyperthermic and hyperkinetic effects of 3,4-methylenedioxymethamphetamine. In the first experiment a single injection of 5.0 or 7.5 mg/kg MDMA produced hyperthermia in rats maintained at aT _a of 24°C but hypothermia in rats maintained at aT _a of 11°C for 24 h prior to the injection. In contrast, hyperkinesis was induced at bothT _as. In the second experiment, the effects of acute MDMA administration was compared in rats maintained at a standardT _a of 24°C and in rats which were placed in a cool (11°C) room for a brief (90-min) period commencing 30 min after the injection. The brief exposure to the cool environment produced significant attenuation of MDMA-induced hyperthermia but did not affect the magnitude of hyperkinesis. The implications of the results for the understanding of the thermotoxic effects of MDMA in human drug users are discussed.     

Studies on the mechanisms underlying amiloride enhancement of 3,4-methylenedioxymethamphetamine-induced serotonin depletion in rats

Amiloride and several of its congeners known to block the Na(+)/Ca(2+) and/or Na(+)/H(+) antiporters potentiate methamphetamine-induced neurotoxicity without altering methamphetamine-induced hyperthermia. We now examine whether amiloride also exacerbates 3,4-methylenedioxymethamphetamine (MDMA)-induced long-term serotonin (5-HT) loss in rats. Amiloride (2.5 mg/kg, every 2 h x 3, i.p.) given at ambient temperature 30 min before MDMA (5 mg/kg, every 2 h x 3, i.p.), markedly exacerbated long-term 5-HT loss. However, in contrast to methamphetamine, amiloride also potentiated MDMA-induced hyperthermia. Fluoxetine (10 mg/kg i.p.) completely protected against 5-HT depletion caused by the MDMA/amiloride combination without significantly altering the hyperthermic response. By contrast, the calcium channel antagonists flunarizine or diltiazem did not afford any protection. Findings with MDMA and amiloride were extended to the highly selective Na(+)/H(+) exchange inhibitor dimethylamiloride, suggesting that the potentiating effects of amiloride are probably mediated by the blockade of Na(+)/H(+) exchange. When the MDMA/amiloride combination was administered at 15 degrees C hyperthermia did not develop and brain 5-HT concentrations remained unchanged 7 days later. Intrastriatal perfusion of MDMA (100 microM for 8 h) in combination with systemic amiloride caused a small depletion of striatal 5-HT content in animals made hyperthermic but not in the striatum of normothermic rats. These data suggest that enhancement of MDMA-induced 5-HT loss caused by amiloride or dimethylamiloride depends on their ability to enhance MDMA-induced hyperthermia. We hypothesise that blockade of Na(+)/H(+) exchange could synergize with hyperthermia to render 5-HT terminals more vulnerable to the toxic effects of MDMA.     

MDMA and 5-HT neurotoxicity: the empirical evidence for its adverse effects in humans - no need for translation

In this issue of the BJP, Green et al. suggest that animal data could not be used to predict the adverse effects of 3,4-methylenedioxymethamphetamine (MDMA) in humans and that MDMA did not produce 5-HT neurotoxicity in the human brain. This proposal was, however, not accompanied by a review of the empirical evidence in humans. The neuroimaging data on 5-HT markers in abstinent recreational ecstasy/MDMA users are extensive and broadly consistent. Reduced levels of the 5-HT transporter (SERT) have been found by research groups worldwide using a variety of assessment measures. These SERT reductions occur across the higher brain regions and remain after controlling for potential confounds. There are also extensive empirical data for impairments in memory and higher cognition, with the neurocognitive deficits correlating with the extent of SERT loss. Hence, MDMA is clearly damaging to humans, with extensive empirical data for both structural and functional deficits.     

Effects of halothane and nitrous oxide anaesthesia on 5-HT turn-over in the rat brain

Summary The effects of anaesthesia with halothane and nitrous oxide on the turn-over of 5-HT in the rat brain were analysed. The rate of 5-HT synthesis was estimated on the basis of 5-HTP accumulation following 5-HTP decarboxylase inhibition. Inhalation anaesthetics reduced the rate of 5-HT synthesis in the whole brain, this effect being particularly marked in the forebrain. In addition, the reduction of the rate of 5-HT synthesis was still detected after a large tryptophan loading indicating that halothane and nitrous oxide anaesthesia reduced the activity of tryptophan hydroxylase in vivo. The utilization of 5-HT was also delayed during anaesthesia since the rate of 5-HT disappearance following the inhibition of its synthesis at the decarboxylation step was decreased in the whole brain. In spite of this reduced turnover of 5-HT in the brain of rats exposed to inhalation anaesthetics, the 5-HIAA levels were permanently elevated. This was the result of a partial inhibition of the active elimination of the acidic metabolite from the brain during this kind of anaesthesia.     

Effect of isolation rearing on 5-HT agonist-induced responses in the rat

Rats were reared from weaning (21 days of age) either in isolation or in social groups of five for 30 days and were then tested for spontaneous locomotor activity and 7 days later for 5-hydroxytryptamine (5-HT) agonist-induced behaviour. Isolation-reared animals displayed locomotor hyperactivity when placed in a novel environment. 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) (2 mg/kg IP) and 8-hydroxy-2-(di-n-propyl-amino) tetralin (8-OH-DPAT) (0.32 mg/kg SC) elicited various components of the 5-HT behavioural syndrome in both groups of animals, with forepaw treading and flat body posture being significantly more pronounced in isolation-reared animals. 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (2.5 mg/kg IP), a 5-HT₂ selective agonist, produced a significantly greater number of back muscle contractions in isolation-reared animals but there was no difference between the two groups in the number of wet-dog shakes produced. Forepaw treading and flat body posture are thought to be mediated by 5-HT_1A receptor activation, and stimulation of this receptor by either 5-MeODMT or 8-OH-DPAT produced greater responding in isolation-reared rats, suggesting supersensitivity of the post-synaptic 5-HT_1A receptor. Wet-dog shakes are thought to be mediated by 5-HT₂ and other (none-5-HT) receptors while back muscle contractions have been shown to be mediated by 5-HT₂ receptors, indicating that there is also an increase in 5-HT₂ receptor responsiveness in the socially-isolated animals. In general, the results indicate post-synaptic 5-HT receptor supersensitivity in isolation-reared rats and these receptor changes may be involved in the behavioural profile observed in such rats.     

脊髓继发性损伤大鼠脊髓前角5-羟色胺阳性细胞的变化研究

目的观察继发性脊髓损伤大鼠5-羟色胺阳性反应物的变化。方法用组织化学和图象分析方法观察大鼠脊髓前角运动神经原内5-羟色胺细胞的变化。结果继发性脊髓损伤大鼠脊髓前角运动神经原5-羟色胺细胞免疫反应减弱（P〈0.01）。结论 5-羟色胺阳性反应物减少这可能与继发性脊髓损伤发生变化有关。     

5-HT_(2B)受体阻断剂对心肌肥厚大鼠心肌5-HT含量及5-HT_(2B)受体表达的影响

目的观察5-HT2B受体阻断剂对去甲肾上腺素(norepinephrine,NE)诱导的心肌肥厚大鼠心肌中5-羟色胺(5-hydrotriptamine,5-HT)含量及5-HT2B受体表达的影响。方法雄性SD大鼠24只,随机分为3组,8只/组,分别为对照组、肥厚组、实验组。采用腹腔注射NE(1.5 mg/kg,2次/d,28 d)的方法建立心肌肥厚模型,自第15天起实验组腹腔注射SB204741(5-HT2B受体阻断剂;2 mg/kg,2次/d),连续注射14 d。对照组腹腔注射相同体积的生理盐水(2次/d,28 d)。检测各组左心室重量与体重之比(LVW/BW)、心肌组织中5-HT的含量及5-HT2B受体的表达情况。结果在NE诱导心肌肥厚过程中,应用SB204741干预可显著减轻心肌肥厚的程度,降低心肌组织中5-HT的含量,并抑制5-HT2B受体表达的上调。结论应用5-HT2B受体阻断剂可减轻NE诱导心肌肥厚的程度,降低心肌组织中5-HT的含量,并抑制5-HT2B受体表达的上调。     

运动后大鼠与正常大鼠纹状体5-羟色胺阳性细胞的比较研究

目的观察负荷运动后大鼠5羟-色胺阳性反应物的变化。方法用组织化学和图象分析方法观察大鼠纹状体神经原内5羟-色胺阳性细胞的变化。结果负荷运动后大鼠纹状体神经原5-羟色胺细胞免疫反应增强(P<0.01)。结论 5羟-色胺阳性反应物增加这可能与大运动量后躯体运动协调性发生变化有关。     

Acute and chronic tryptophan depletion differentially regulate central 5-HT1A and 5-HT2A receptor binding in the rat

Rationale Tryptophan depletion is used to reduce central serotonergic function and to investigate its role in psychiatric illness. Despite widespread clinical use, its effects on serotonin (5-HT) receptors have not been well characterized. Objective The aim of this study was to examine the effect of acute (ATD) and chronic tryptophan depletion (CTD) on free-plasma tryptophan (TRP), central TRP and 5-HT and brain 5-HT_1A and 5-HT_2A receptor binding in the rat. Methods TRP and 5-HT were measured by high-performance liquid chromatography and receptor levels determined by homogenate radioligand binding and in-vitro receptor autoradiography. Results Free-plasma TRP, central TRP and central 5-HT levels were significantly and similarly reduced by ATD and 1- and 3-week CTD compared to controls. ATD significantly reduced 5-HT_1A binding in the dorsal raphe (14%) but did not significantly alter postsynaptic 5-HT_1A binding (frontal cortex, remaining cortex and hippocampus) or 5-HT_2A binding (cortex and striatum). One-week CTD did not significantly alter cortical 5-HT_2A binding or postsynaptic 5-HT_1A binding. Furthermore, 3-week CTD did not significantly alter 5-HT_1A binding but significantly increased cortical 5-HT_2A binding without affecting striatal or hippocampal levels. In the CTD 1 and 3-week groups, rat body weight was significantly decreased as compared to controls. However, weight loss was not a confounding factor for decreased cortical 5-HT_2A-receptor binding. Conclusion ATD-induced reduction in somatodendritic 5-HT_1A autoreceptor binding may represent an intrinsic ‘homeostatic response’ reducing serotonergic feedback in dorsal raphe projection areas. In contrast, the increase in 5-HT_2A receptor after CTD may be a compensatory response to a long-term reduction in 5-HT.     

Pharmacological characterisation of 5-HT receptors positively coupled to adenylyl cyclase in the rat hippocampus

The pharmacological properties of 5-hydroxytryptamine (5-HT) receptors positively coupled to adenylyl cyclase in the rat hippocampus were investigated using selective agonists and antagonists. 5-HT (0.008–125 μM) stimulated cyclic AMP formation in homogenates of rat hippocampus in a concentration-dependent manner. The maximal increase in cyclic AMP formation occurred at 1 μM (141 ± 6%) and the half-maximal effect (EC₅₀) at 50 ± 22 nM. Cyclic AMP accumulation induced by 1 μM 5-HT was partly inhibited by the selective 5-HT_1A receptor antagonist WAY 100,635 (1 μM), the selective 5-HT₄ receptor antagonist SB 203,186 (1 μM), and the 5-HT_2A/C/ 5-HT₇ receptor antagonist mesulergine (25 μM). WAY 100,635, SB 203,186 and mesulergine inhibited the effect of 5-HT (1 μM) by 47%, 33% and 49%, respectively. The combination of WAY 100,635 (1 μM) with SB 203,186 (1 μM) or mesulergine (25 μM) resulted in stronger inhibition than with each antagonist alone, and the combination of all three antagonists produced almost total blockade (95%) of 5-HT-induced cyclic AMP accumulation. 5-Carboxamidotryptamine (5-CT; 0.008–125 μM), a 5-HT₁/5-HT₇ receptor agonist, and SDZ 216–454 (0.008– 125 μM), a selective 5-HT₄ receptor agonist, concentration-dependently stimulated cyclic AMP formation, but the maximal effect of each agonist was smaller than that of 5-HT alone. SDZ 216–454 (5 μM) and 5-CT (5 μM) in combination stimulated cyclic AMP formation in an additive manner. 8-OH-PIPAT and 8-OH-DPAT, two selective 5-HT_1A agonists, produced a small but significant increase in cyclic AMP formation at concentrations above 0.04 μM and 10 μM, respectively. These findings suggest that at least three 5-HT receptor subtypes, i.e. 5-HT_1A, 5-HT₇ and 5-HT₄ receptors, are involved in mediating 5-HT-induced cyclic AMP formation in rat hippocampus. Received: 28 October 1998 / Accepted: 16 March 1999     

Synergism between 5-HT1B/1D and 5-HT1A receptor antagonists on turnover and release of 5-HT in guinea-pig brain in vivo

The effects on 5-HT turnover (5-HIAA/5-HT ratio) and extracellular 5-HT and 5-HIAA levels (in vivo microdialysis in freely moving animals) were analysed in guinea-pig brains following the 5-HT_1B receptor antagonist, GR 127935 {N-[4-methoxy-3-(4-methyl-1-piper_{azinyl)phenyl]-2’-methyl-4’-(5-methyl-1,2,4-oxadiazol-3-}yl) [1,1-biphenyl]-4-carboxamide}, or the 5-HT_1A receptor antagonist, WAY-100635 (N-{2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl}-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride), administered alone or in combination. GR 127935, injected alone, increased 5-HT turnover with maximal effects approximately 50% above the control levels in the four brain regions examined (hypothalamus, hippocampus, striatum and frontal cortex). GR 127935 significantly increased extracellular concentrations of 5-HT and 5-HIAA in frontal cortex (40%), whereas 5-HIAA, but not 5-HT, was elevated in striatum (20–30%). WAY-100635 did not significantly change 5-HT turnover but caused a small significant increase in the extracellular 5-HT and 5-HIAA concentrations in both striatum and frontal cortex. The combined treatment with GR 127935 and WAY-100635 resulted in an increased 5-HT turnover reaching maximal effects of 70–90% above the control values in all brain regions tested and produced a significant elevation of striatal and frontal cortex extracellular 5-HT (40% and 60%, respectively) and 5-HIAA (60% and 70%, respectively) concentrations. The synergistic effect of the two receptor antagonists on the 5-HT turnover and the terminal release of 5-HT indicate somatodendritic 5-HT release and stimulation of inhibitory 5-HT_1A receptors at this level. Extracellular 5-HIAA seems to be a better marker than 5-HT itself for the evoked 5-HT release when the reuptake mechanism is intact. Received: 2 September 1998 / Accepted: 19 November 1998     

Behavioural analysis of the acute and chronic effects of MDMA treatment in the rat

  Rationale: A variety of animal models have shown MDMA (3,4-methylenedioxymethamphetamine) to be a selective 5-HT neurotoxin, though little is known of the long-term behavioural effects of the pathophysiology. The widespread recreational use of MDMA thus raises concerns over the long-term functional sequelae in humans. Objective: This study was designed to explore both the acute- and post-treatment consequences of a 3-day neurotoxic exposure to MDMA in the rat, using a variety of behavioural paradigms. Methods: Following training to pretreatment performance criteria, animals were treated twice daily with ascending doses of MDMA (10, 15, 20 mg/kg) over 3 days. Body temperature, locomotor activity, skilled paw-reaching ability and performance of the delayed non-match to place (DNMTP) procedure was assessed daily during this period and on an intermittent schedule over the following 16 days. Finally, post mortem biochemical analyses of [³H] citalopram binding and monoamine levels were performed. Results: During the MDMA treatment period, an acute 5-HT-like syndrome was observed which showed evidence of tolerance. Once drug treatment ceased the syndrome abated completely. During the post-treatment phase, a selective, delay-dependent, deficit in DNMTP performance developed. Post-mortem analysis confirmed reductions in markers of 5-HT function, in cortex, hippocampus and striatum. Conclusions: These results confirm that acutely MDMA exposure elicits a classical 5-HT syndrome. In the long-term, exposure results in 5-HT neurotoxicity and a lasting cognitive impairment. These results have significant implications for the prediction that use of MDMA in humans could have deleterious long-term neuropsychological/psychiatric consequences. Received: 31 August 1998 / Final version: 25 November 1998     

Multiple 5-HT receptors are involved in the effects of acute MDMA treatment: studies on locomotor activity and responding for conditioned reinforcement

RATIONALE: Responding for conditioned reinforcement is increased by the dopamine releasing agent amphetamine, but reduced by drugs that enhance serotonin (5-HT) function. The amphetamine derivative 3,4-methylenedioxymethamphetamine (MDMA, Ecstasy) releases both monoamines. OBJECTIVES: The primary purpose of this study was to examine the effects of MDMA on responding for conditioned reinforcement as well as on locomotor activity. The roles of several 5-HT receptor sub-types in mediating these behavioural effects of MDMA were also examined. METHODS: Locomotion was measured in photocell activity monitors. For conditioned reinforcement experiments thirsty rats learned to associate a conditioned stimulus (CS) with water in operant chambers. Subsequently, two response levers were available; responding on one lever delivered the CS, while responding on the second lever had no consequences. Drug effects on this operant response were measured. RESULTS: MDMA dose-dependently increased locomotion but reduced responding for conditioned reinforcement. This latter effect differs from that induced by amphetamine, which potentiates conditioned reinforcement responding. The stimulant effect of MDMA was attenuated by GR127935 and ketanserin, indicating facilitatory roles of 5-HT(1B) and 5-HT(2A) receptors in mediating this effect. The 5-HT(2C) antagonist SB242084 enhanced the stimulant effect of MDMA. Only SB242084 attenuated the suppressant effect of MDMA on responding for conditioned reinforcement. CONCLUSIONS: The results show that 5-HT(2A) and 5-HT(1B/1D) receptors play a facilitatory role in mediating the stimulant effect of MDMA, whereas 5-HT(2C) receptors are inhibitory. Activation of 5-HT(2C) receptors also contributes to the deficit in operant responding. Multiple 5-HT receptor sub-types appear to contribute to the behavioural effects of MDMA.     

Vortioxetine,but not escitalopram or duloxetine,reverses memory impairment induced by central 5-HT depletion in rats: Evidence for direct 5-HT receptor modulation

Depressed patients suffer from cognitive dysfunction, including memory deficits. Acute serotonin (5-HT) depletion impairs memory and mood in vulnerable patients. The investigational multimodal acting antidepressant vortioxetine is a 5-HT₃, 5-HT₇ and 5-HT_1D receptor antagonist, 5-HT_1B receptor partial agonist, 5-HT_1A receptor agonist and 5-HT transporter (SERT) inhibitor that enhances memory in normal rats in novel object recognition (NOR) and conditioned fear (Mørk et al., 2013). We hypothesized that vortioxetine's 5-HT receptor mechanisms are involved in its memory effects, and therefore investigated these effects in 5-HT depleted rats. Four injections of the irreversible tryptophan hydroxylase inhibitor 4-chloro-dl-phenylalanine methyl ester hydrochloride (PCPA, 86 mg/kg, s.c.) induced 5-HT depletion, as measured in hippocampal homogenate and microdialysate. The effects of acute challenge with vortioxetine or the 5-HT releaser fenfluramine on extracellular 5-HT were measured in PCPA-treated and control rats. PCPA's effects on NOR and spontaneous alternation (SA) performance were assessed along with the effects of acute treatment with 5-hydroxy-l-tryptophan (5-HTP), vortioxetine, the selective 5-HT reuptake inhibitor escitalopram, or the 5-HT norepinephrine reuptake inhibitor duloxetine. SERT occupancies were estimated by ex vivo autoradiography. PCPA depleted central 5-HT by >90% in tissue and microdialysate, and impaired NOR and SA performance. Restoring central 5-HT with 5-HTP reversed these deficits. At similar SERT occupancies (>90%) vortioxetine, but not escitalopram or duloxetine, restored memory performance. Acute fenfluramine significantly increased extracellular 5-HT in control and PCPA-treated rats, while vortioxetine did so only in control rats. Thus, vortioxetine restores 5-HT depletion impaired memory performance in rats through one or more of its receptor activities.     

Biochemical evidence for the 5-HT agonist properties of PAT (8-hydroxy-2-(di-n-propylamino)tetralin) in the rat brain

In vitro investigations revealed that PAT (8-hydroxy-2-(n-dipropylamino)tetralin) interacted with postsynaptic 5-HT receptors in the rat brain: the drug stimulated 5-HT-sensitive adenylate cyclase in homogenates of colliculi from new-born rats (K_Aapp 8.6 μM) and inhibited the specific binding of [³H]5-HT to 5-HT₁ sites. The PAT-induced inhibition of [³H]5-HT binding showed marked regional differences compatible with a preferential interaction of PAT (IC₅₀ 2 nM) with the 5-HT_1A subclass. As previously seen with 5-HT agonists, the efficacy of PAT for displacing [³H]5-HT bound to hippocampal membranes was markedly increased by Mn²⁺ (1 nM) and reduced by GTP (0.1 nM). PAT also affected presynaptic 5-HT metabolism since it inhibited competitively (K_i 1.4 μM) [³H]5-HT uptake into cortical synaptosomes and reduced (in the presence of the 5-HT uptake inhibitor fluoxetine) the K⁺-evoked release of [³H]5-HT previously taken up or newly synthesized from [³H]tryptophan in cortical or striatal slices. This latter effect was prevented by 5-HT antagonists (methiothepin, metergoline) suggesting that it was mediated by the stimulation of presynaptic 5-HT autoreceptors by PAT. Like 5-HT, PAT counteracted the stimulatory effect of K⁺-induced depolarization on the synthesis of [³H]5-HT from [³H]tryptophan in cortical slices. It is concluded that PAT is a potent 5-HT agonist acting on both post- and presynaptic 5-HT receptors in the rat brain.     

Effect of electroshock on 5-HT metabolism in rat brain

Repeated electroshock treatment (EST) on three consecutive days was administered to 72 rats. The last treatment was given immediately after an injection of a tryptophan-hydroxylase inhibitor, H 22/54. The animals were killed three hours later, two to four brain stems were pooled, analysed for 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) and the values compared with a group of animals receiving H 22/54 only. A significant decrease in 5-HT was seen in the EST group indicating an increase in the release of 5-HT after the repeated treatment. When the level of 5-HIAA in the EST group was compared with the level in the group treated with H 22/54 alone, the difference was slight. The small increase could be explained by the rather slow turnover rate of 5-HT in the central nervous system (CNS) and thus of the synthesis of 5-HIAA. The possibility of an accelerated outflow of 5-HIAA from the CNS after EST should also be considered.