A study of the mechanism of MDMA ('ecstasy')-induced neurotoxicity of 5-HT neurones using chlormethiazole, dizocilpine and other protective compounds.

1. An investigation has been made in rats into the neurotoxic effect of the relatively selective 5-hydroxytryptamine (5-HT) neurotoxin, 3,4-methylenedioxymethamphetamine (MDMA or 'Ecstasy') using chlormethiazole and dizocilpine, both known neuroprotective compounds and also gamma-butyrolactone, ondansetron and pentobarbitone. 2. Administration of MDMA (20 mg kg-1, i.p.) resulted in a 50% loss of cortical and hippocampal 5-HT and 5-hydroxyindole acetic acid (5-HIAA) 4 days later. This reflects the long term neurotoxic loss of 5-HT that occurs. Injection of gamma-butyrolactone (GBL; 400 mg kg-1, i.p.) 5 min before and 55 min after the MDMA provided substantial protection. Pentobarbitone (25 mg kg-1, i.p.) using the same dose regime was also protective, but ondansetron (0.5 mg kg-1 or 0.1 mg kg-1, i.p.) was without effect. 3. MDMA (20 mg kg-1) had no significant effect on striatal dopamine concentration 4 days later but did produce a small decrease in 3,4-dihydroxyphenylacetic acid (DOPAC) content. There were few significant changes in rats given MDMA plus GBL, ondansetron or pentobarbitone. 4. A single injection of MDMA (20 mg kg-1, i.p.) resulted in a greater than 80% depletion of 5-HT in hippocampus and cortex 4 h later, reflecting the initial rapid release that had occurred. None of the neuroprotective compounds (chlormethiazole, 50 mg kg-1; dizocilpine, 1 mg kg-1; GBL, 400 mg kg-1; pentobarbitone, 25 mg kg-1) given 5 min before and 55 min after the MDMA injection, altered the degree of 5-HT loss. 5. Acute MDMA injection increased striatal dopamine content (28%) and decreased the DOPAC content. In general, administration of the drugs under investigation did not significantly alter these MDMA-induced changes. Both chlormethiazole and GBL produced a greater increase in dopamine than MDMA alone, but this was apparently an additive effect to the action of either drug alone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chlormethiazole, dizocilpine and haloperidol prevent the degeneration of serotonergic nerve terminals induced by administration of MDMA (‘Ecstasy’) to rats

An investigation has been made into the effect of 3,4-methylenedioxymethamphetamine (MDMA or ‘Ecstasy’) administration on the concentration of 5-hydroxytryptamine (5-HT), uptake of [³H]5-HT and [³H]paroxetine binding in rat cerebral cortex tissue. Four days after 2 injections of MDMA (20 mg/kg i.p., 6 hr apart) the concentrations of 5-HT and its metabolite 5-HIAA were reduced by 60%. The binding of [³H]paroxetine to the presynaptic 5-HT transporter was decreased and high affinity uptake of [³H]5-HT was reduced by a similar amount, indicating neurodegeneration of 5-HT terminals. Pretreatment with chlormethiazole (100 mg/kg i.p.), 10 min before each MDMA injection prevented the decrease in both [³H]parotextine binding and uptake of [³H]5-HT. The loss in 5-HT and 5-HIAA content was also attenuated. Pretreatment with dizocilpine (1 mg/kg i.p.) or haloperidol (2 mg/kg i.p.) also prevented the MDMA-induced loss of [³H]paroxetine binding and attenuated the loss of 5-HT and 5-HIAA content. All three compounds also decreased the degree of hyperthermia that follows MDMA administration, although previous studies suggest that the long term neurodegeneration is not associated with the acute hyperthermic response. These data support the findings of others that MDMA injection produces degeneration of 5-HT nerve terminals in the cortex, confirm that chlormethiazole, dizocilpine and haloperidol attenuate MDMA-induced neurotoxic loss of 5-HT and demonstrate for the first time that these compounds prevent the neurodegeneration of 5-HT nerve terminals that follows MDMA administration.     

Neuroprotective activity of chlormethiazole following transient forebrain ischaemia in the gerbil.

1. The effect of chlormethiazole, and other drugs which potentiate gamma-aminobutyric acid (GABA) function on delayed neuronal death in the hippocampus has been examined in the gerbil. 2. Chlormethiazole (100 mg kg-1, i.p.) and two other drugs previously reported to be neuroprotective (dizocilpine, 3 mg kg-1, i.p. and ifenprodil, 4 mg kg-1, i.p.) were all found to prevent neurodegeneration of CA1/CA2 neurones in the hippocampus when given 30 min before a 5 min episode of bilateral carotid artery occlusion. 3. Chlormethiazole (100 mg kg-1) was neuroprotective when given up to 3 h, after the ischaemic episode. 4. Given 1 h after the cartoid artery occlusion, chlormethiazole produced significant protection against hippocampal neurodegeneration at a dose of 50 mg kg-1, but not at 25 mg kg-1. 5. Phenobarbitone (100 mg kg-1, i.p.) and Saffan (alphaxalone, 45 mg kg-1 plus alphadalone, 15 mg kg-1, i.p.) were not protective when given 1 h after the ischaemic episode while pentobarbitone (30 mg kg-1, i.p.) had a modest protective effect. 6. Evidence is presented to show that neither the operating procedure nor the chlormethiazole administration lowered rectal or cerebral temperature. 7. The data suggest that chlormethiazole may be a useful treatment in the prevention of neurodegeneration following stroke or cardiac arrest.     

Striatal dopamine release in vivo following neurotoxic doses of methamphetamine and effect of the neuroprotective drugs, chlormethiazole and dizocilpine.

1. Administration to rats of methamphetamine (15 mg kg-1, i.p.) every 2 h to a total of 4 doses resulted in a neurotoxic loss of striatal dopamine of 36% and of 5-hydroxytryptamine (5-HT) in the cortex (43%) and hippocampus (47%) 3 days later. 2. Administration of chlormethiazole (50 mg kg-1, i.p.) 15 min before each dose of methamphetamine provided complete protection against the neurotoxic loss of monoamines while administration of dizocilpine (1 mg kg-1, i.p.) using the same dose schedule provided substantial protection. 3. Measurement of dopamine release in the striatum by in vivo microdialysis revealed that methamphetamine produced an approximate 7000% increase in dopamine release after the first injection. The enhanced release response was somewhat diminished after the third injection but still around 4000% above baseline. Dizocilpine (1 mg kg-1, i.p.) did not alter this response but chlormethiazole (50 mg kg-1, i.p.) attenuated the methamphetamine-induced release by approximately 40%. 4. Dizocilpine pretreatment did not influence the decrease in the dialysate concentration of the dopamine metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) produced by administration of methamphetamine while chlormethiazole pretreatment decreased the dialysate concentration of these metabolites still further. 5. The concentration of dopamine in the dialysate during basal conditions increased modestly during the course of the experiment. This increase did not occur in chlormethiazole-treated rats. HVA concentrations were unaltered by chlormethiazole administration. 6. Chlormethiazole (100-1000 microM) did not alter methamphetamine (100 microM) or K+ (35 mM)-evoked release of endogenous dopamine from striatal prisms in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)     

The neurotoxic effects of methamphetamine on 5-hydroxytryptamine and dopamine in brain: evidence for the protective effect of chlormethiazole.

Studies were undertaken in mice and rats on the neurotoxic effects of methamphetamine on dopaminergic and 5-hydroxytryptaminergic neurones in the brain and the neuroprotective action of chlormethiazole. In initial studies, mice were injected with methamphetamine (5 mg/kg, i.p.) at 2 hr intervals, to a total of 4 times. This procedure produced a 66% loss of striatal dopamine and a 50% loss of tyrosine hydroxylase activity 3 days later. Chlormethiazole (50 mg/kg, i.p.), given 15 min before each dose of methamphetamine, totally prevented the methamphetamine-induced loss of tyrosine hydroxylase activity and partly prevented the loss of dopamine. Phencyclidine (20 mg/kg, i.p.), given in place of chlormethiazole, also prevented the loss of tyrosine hydroxylase. Administration to rats of 4 doses of methamphetamine (15 mg/kg, i.p.) at 3 hr intervals resulted in a 75% loss of striatal dopamine 3 days later and a similar loss of 5-HT and 5-HIAA in cortex and hippocampus. Chlormethiazole (50 mg/kg, i.p.), given 15 min before each injection of methamphetamine, protected against the loss of dopamine and indoleamine content, in the respective regions. Pentobarbital (25 mg/kg, i.p.) also provided substantial protection but diazepam (2.5 mg/kg, i.p.) was without effect. Confirming earlier studies, dizocilpine (1 mg/kg) also provided substantial protection against the methamphetamine-induced neurotoxicity. Preliminary data indicated that chlormethiazole was not neuroprotective because of a hypothermic action. These data therefore demonstrate that chlormethiazole is an effective neuroprotective agent against methamphetamine-induced neurotoxicity and extend the evidence for the possible value of this drug in preventing neurodegeneration.     

Chlormethiazole and Dizocilpine Block the Behavioural,but Not the Neurotoxic Effects of 5,7-Dihydroxytryptamine in Mice

Intracerebroventricular administration to mice of 5,7-dihydroxytryptamine at a dose of 300 μg resulted in convulsive behaviour and death (latency 7.6±1.7 min.). Pretreatment with dizocilpine or chlormethiazole resulted in a dose dependent inhibition of the convulsive behaviour. A dose of dizocilpine of 0.12 μmol/kg or chlormethiazole at a dose of 150 μmol/kg prevented seizures for 30 min. Injection of 5,7-dihydroxytryptamine (75 μg, intracerebroventricularly) produced an approximate 50% neurotoxic loss of cerebral 5-hydroxytryptamine (5-HT) and its metabolite 5-hydroxyindole acetic acid (5-HIAA) 8 days later. This loss was not prevented by administration of either dizocilpine (4.5 μmol/kg intraperitoneally) or chlormethiazole (300 μmol/kg intraperitoneally) given 5 min. before and 55 min. after the 5,7-dihydroxytryptamine injection. It is proposed that chlormethiazole and dizocilpine may protect against 5,7-dihydroxytryptamine-induced seizures because of their anticonvulsant activity, but that they do not prevent the neurotoxic effects of the compound. The data also suggest that the neurotoxic effects of substituted amphetamines such as 3,4-methylene dioxymethamphetamine (MDMA or Ecstasy) do not result from the formation of a 5,7-dihydroxytryptamine like compound.     

The hyperthermic and neurotoxic effects of 'Ecstasy' (MDMA) and 3,4 methylenedioxyamphetamine (MDA) in the Dark Agouti (DA) rat, a model of the CYP2D6 poor metabolizer phenotype.

1. The effect of administration of 3,4-methylenedioxymethamphetamine (MDMA or 'Ecstasy') and its N-demethylated product, 3,4-methylenedioxyamphetamine (MDA) on both rectal temperature and long term neurotoxic loss of cerebral 5-hydroxytryptamine (5-HT) has been studied in male and female Dark Agouti (DA) rats. The female metabolizes debrisoquine more slowly than the male and its use has been suggested as a model of the human debrisoquine 4-hydroxylase poor metabolizer phenotype. 2. A novel h.p.l.c. method was developed and used to measure plasma MDMA and MDA concentrations in the DA rats. 3. The hyperthermic response following MDMA was enhanced in female rats. Plasma MDMA concentrations were also 57% higher than in males 45 min post-injection, while plasma concentrations of MDA were 48% lower. 4. Plasma concentrations of MDMA and MDA in male rats were unaffected by pretreatment with proadifen (15 mg kg-1) or quinidine (60 mg kg-1), but the hyperthermic response to MDMA (10 mg kg-1, i.p.) was enhanced by quinidine pretreatment. 5. The hyperthermic response following MDA was greater in male DA rats, despite plasma drug concentrations being 40% higher in females 60 min after injection. 6. Seven days after a single dose of MDMA (10 mg kg-1, i.p.) there was a substantial loss in the concentration of 5-HT and 5-hydroxyindoleacetic acid (5-HIA) in cortex and hippocampus. [3H]-paroxetine binding was also decreased by 27% in the cortex, indicating that the amine loss reflected a neurodegenerative change. MDMA (5 mg kg-1, i.p.) was without effect on brain 5-HT content.(ABSTRACT TRUNCATED AT 250 WORDS)     

An in vivo dialysis and behavioural study of the release of 5-HT by p-chloroamphetamine in reserpine-treated rats.

1. Reserpine (2.5 mg kg-1 i.p.) decreased rat brain 5-hydroxytryptamine (5-HT) by 86% 24 h later but most components of the 5-HT-dependent behavioural syndrome induced by p-chloroamphetamine (PCA, 5 mg kg-1 i.p.) or 5-methoxy-N,N-dimethyltryptamine (5-MeODMT, 5 mg kg-1 i.p.) over 1 h after administration were unaffected. However, Straub tail was increased after giving PCA or 5-MeODMT and head weaving was decreased after giving 5-MeODMT. 2. Frontal cortex extracellular 5-HT concentrations of vehicle pretreated rats before injection of PCA, as calculated from dialysate 5-HT concentrations, were about 1/1000th of corresponding brain values. Extracellular 5-hydroxyindoleacetic acid (5-HIAA) and brain values were comparable with each other. Dialysate 5-HT increased after PCA with peak values at 20-40 min. 3. Reserpine pretreatment reduced dialysate 5-HT concentration before PCA was given but the net increase (AUC) over the 1 h after PCA did not differ significantly from that seen in animals pretreated with vehicle. Dialysate 5-HIAA values slowly decreased after PCA injection in both reserpine and vehicle pretreated groups. 4. The results suggest that PCA causes the 5-HT syndrome by releasing 5-HT from the neuronal cytoplasm but that physiological release of 5-HT occurs from vesicular stores.     

The mechanisms involved in the long-lasting neuroprotective effect of fluoxetine against MDMA ('ecstasy')-induced degeneration of 5-HT nerve endings in rat brain

1. It has been reported that co-administration of fluoxetine with 3,4-methylenedioxymethamphetamine (MDMA, 'ecstasy') prevents MDMA-induced degeneration of 5-HT nerve endings in rat brain. The mechanisms involved have now been investigated. 2. MDMA (15 mg kg(-1), i.p.) administration produced a neurotoxic loss of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in cortex, hippocampus and striatum and a reduction in cortical [3H]-paroxetine binding 7 days later. 3. Fluoxetine (10 mg kg(-1), i.p., x2, 60 min apart) administered concurrently with MDMA or given 2 and 4 days earlier provided complete protection, and significant protection when given 7 days earlier. Fluvoxamine (15 mg kg(-1), i.p., x2, 60 min apart) only produced neuroprotection when administered concurrently. Fluoxetine (10 mg kg(-1), x2) markedly increased the K(D) and reduced the B(max) of cortical [3H]-paroxetine binding 2 and 4 days later. The B(max) was still decreased 7 days later, but the K(D) was unchanged. [3H]-Paroxetine binding characteristics were unchanged 24 h after fluvoxamine (15 mg kg(-1), x2). 4. A significant cerebral concentration of fluoxetine plus norfluoxetine was detected over the 7 days following fluoxetine administration. The fluvoxamine concentration had decreased markedly by 24 h. 5. Pretreatment with fluoxetine (10 mg kg(-1), x2) failed to alter cerebral MDMA accumulation compared to saline pretreated controls. 6. Neither fluoxetine or fluvoxamine altered MDMA-induced acute hyperthermia. 7. These data demonstrate that fluoxetine produces long-lasting protection against MDMA-induced neurodegeneration, an effect apparently related to the presence of the drug and its active metabolite inhibiting the 5-HT transporter. Fluoxetine does not alter the metabolism of MDMA or its rate of cerebral accumulation.     

Effects of idebenone (CV-2619) on metabolism of monoamines, especially serotonin, in the brain of normal rats and rats with cerebral ischemia

The effects of 6-(10-hydroxydecyl)-2,3-dimethoxy-5-methyl-1,4-benzoquinone (idebenone, CV-2619) on the contents, turnover, release and uptake of monoamines, especially serotonin (5-HT), in various brain regions of Wistar rats were studied in vivo and in vitro. In normal rats, an intraperitoneal (i.p.) dose of 100 mg/kg of CV-2619 had no significant effect on the levels of norepinephrine (NE), dopamine (DA) and their metabolites, and 5-HT in the brain regions examined, but it increased the levels of 5-hydroxyindole-3-acetic acid (5-HIAA), the main metabolite of 5-HT, in many brain regions. In rats with cerebral ischemia, a low dose (10 mg/kg, i.p.) of CV-2619 normalized the decreased levels of 5-HIAA in the cerebral cortex, hippocampus, diencephalon and brain stem. A 5-HT biosynthesis inhibitor, DL-p-chlorophenylalanine (PCPA, 150 mg/kg, i.p.), decreased the levels of 5-HT in all brain regions to one-third of the control levels 24 hr after administration in normal rats. CV-2619 (10, 30 or 100 mg/kg, i.p.), administered 24 hr after the treatment with PCPA, accelerated the PCPA-induced 5-HT decreases in the hippocampus, diencephalon and brain stem in a dose-dependent manner. In vitro CV-2619, like p-chloroamphetamine (PCA), stimulated 5-HT release from slices of the hippocampus and diencephalon. CV-2619 slightly inhibited and PCA markedly inhibited 5-HT uptake into hippocampal slices. The mechanism of the 5-HT releasing action of CV-2619 in hippocampal slices seems to be mediated through endogenous calcium. These results suggest that CV-2619 has an enhancing effect on the turnover of 5-HT in the hippocampus, diencephalon and brain stem of rats.     

Effect of GBR 12909 and fluoxetine on the acute and long term changes induced by MDMA ('ecstasy') on the 5-HT and dopamine concentrations in mouse brain

We examined the long term effect of 3,4 methylenedioxymethamphetamine (MDMA, 10, 20 and 30 mg/kg, i.p.) on the cerebral 5-hydroxytryptamine (5-HT) and dopamine content in Swiss Webster mice. Three injections of MDMA (20 or 30 mg/kg, i.p.) given 3 h apart produced a marked depletion in the striatal content of dopamine and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) 7 days later. None of the doses administered altered the concentration of 5-HT or its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in several brain areas. Pre-treatment with the dopamine uptake inhibitor GBR 12909 (10 mg/kg, i.p.), 30 min before each of the three MDMA (30 mg/kg, i.p.) injections, completely prevented the long term loss in the striatal catechol concentrations. However, GBR 12909 (10 mg/kg, i.p.) not only failed to prevent the acute effects induced by MDMA (30 mg/kg x 3, i.p.) on dopamine metabolism 30 min later, but in fact potentiated them. The 5-HT uptake inhibitor, fluoxetine (10 mg/kg, i. p.) failed to prevent both the acute and long term dopaminergic deficits. MDMA (30 mg/kg x 3) altered the body temperature of the mice biphasically, producing a rapid hyperthermia followed by prolonged hypothermia. In contrast, MDMA (20 mg/kg x 3) produced an initial hypothermia followed by hyperthermia. The present experiments therefore appear to rule out any direct relationship between the neurotoxic effects of MDMA and its acute effects on body temperature in mice. Fluoxetine administered 30 min before each MDMA (30 mg/kg) injection prevented these temperature changes, while GBR 12909 was without effect. This suggests that the neuroprotective effect of GBR 12909 against MDMA-induced neurotoxicity is not directly related to its ability to inhibit the MDMA-induced acute effects on dopamine metabolism or alter the MDMA-induced temperature change. The data illustrate major differences in the neurotoxic profile of MDMA in mice and rats.     

Increased total activity in the rat after L-tryptophan plus the monoamine oxidase-A inhibitor amiflamine but not after L-tryptophan plus clorgyline.

The effect of pretreatment with either saline or the monoamine oxidase-A inhibitors clorgyline and amiflamine upon the total activity, locomotion and rearing behaviour of the rat induced by various doses of the monoamine precursor L-tryptophan was studied by use of automated activity boxes. Amiflamine (2.5 and 5.0 mg kg-1, i.p.) increased in a dose-dependent manner total activity and to a lesser extent, locomotion when given 60 min before L-tryptophan (100 mg kg-1, i.p.). The increased activity was seen after amiflamine plus either 25 or 75 mg kg-1 L-tryptophan. Rearing behaviour was not affected. Analysis of 5-hydroxytryptamine (5-HT) and its deaminated metabolite 5-hydroxyindoleacetic acid (5-HIAA) by high performance liquid chromatography with electrochemical detection indicated that in both frontal cortex and hypothalamus, amiflamine (at both doses) increased 5-HT and reduced 5-HIAA concentrations. Combination of amiflamine with L-tryptophan (100 mg kg-1, i.p.) resulted in a higher 5-HT concentration being found than after amiflamine alone. L-Tryptophan treatment alone did not change 5-HT concentrations but increased 5-HIAA concentrations. Clorgyline, at a dose of either 1 or 5 mg kg-1 i.p. plus L-tryptophan (25 or 100 mg kg-1, i.p.) did not increase total activity, locomotion or behaviour. A number of possible explanations for the differences in the behavioural effects of clorgyline and amiflamine when given with L-tryptophan are discussed. It is concluded that in addition to monoamine oxidase-A inhibition, other pharmacological effects of the drugs, such as 5-HT release (amiflamine) and inhibition of tryptophan hydroxylation (clorgyline) may be of importance in determining the magnitude of the increase in activity when the compounds are given together with L-tryptophan.     

Reduction in brain serotonin markers by alpha-ethyltryptamine (Monase).

alpha-Ethyltryptamine (Monase) is both an inhibitor of monoamine oxidase and a monoamine releasing agent. To determine whether alpha-ethyltryptamine induces serotonergic deficits similar to that of other monoamine releasing agents such as 3,4-methyl-enedioxymethamphetamine (MDMA) and para-chloroamphetamine (PCA), rats were given multiple doses (8 x 30 mg/kg s.c.) of alpha-ethyltryptamine acetate. Serotonin and 5-hydroxyindole acetic acid (5-HIAA) levels and the number of 5-HT uptake sites (determined from [3H]paroxetine binding) were significantly decreased in frontal cortex samples at one week killing. A significant decrease in 5-HT and 5-HIAA levels was also observed in rat hippocampal samples. The results provide evidence that alpha-ethyltryptamine may induce serotonin neurotoxicity similar to that of MDMA and PCA.     

Studies on the role of dopamine in the degeneration of 5-HT nerve endings in the brain of Dark Agouti rats following 3,4-methylenedioxymethamphetamine (MDMA or 'ecstasy') administration

1. We investigated whether dopamine plays a role in the neurodegeneration of 5-hydroxytryptamine (5-HT) nerve endings occurring in Dark Agouti rat brain after 3,4-methylenedioxymethamphetamine (MDMA or 'ecstasy') administration. 2. Haloperidol (2 mg kg(-1) i.p.) injected 5 min prior and 55 min post MDMA (15 mg kg(-1) i.p.) abolished the acute MDMA-induced hyperthermia and attenuated the neurotoxic loss of 5-HT 7 days later. When the rectal temperature of MDMA + haloperidol treated rats was kept elevated, this protective effect was marginal. 3. MDMA (15 mg kg(-1)) increased the dopamine concentration in the dialysate from a striatal microdialysis probe by 800%. L-DOPA (25 mg kg(-1) i.p., plus benserazide, 6.25 mg kg(-1) i.p.) injected 2 h after MDMA (15 mg kg(-1)) enhanced the increase in dopamine in the dialysate, but subsequent neurodegeneration was unaltered. L-DOPA (25 mg kg(-1)) injected before a sub-toxic dose of MDMA (5 mg kg(-1)) failed to induce neurodegeneration. 4. The MDMA-induced increase in free radical formation in the hippocampus (indicated by increased 2,3- and 2,5-dihydroxybenzoic acid in a microdialysis probe perfused with salicylic acid) was unaltered by L-DOPA. 5. The neuroprotective drug clomethiazole (50 mg kg(-1) i.p.) did not influence the MDMA-induced increase in extracellular dopamine. 6. These data suggest that previous observations on the protective effect of haloperidol and potentiating effect of L-DOPA on MDMA-induced neurodegeneration may have resulted from effects on MDMA-induced hyperthermia. 7. The increased extracellular dopamine concentration following MDMA may result from effects of MDMA on dopamine re-uptake, monoamine oxidase and 5-HT release rather than an 'amphetamine-like' action on dopamine release, thus explaining why the drug does not induce degeneration of dopamine nerve endings.     

Actions of 5-HT1 ligands on excitatory synaptic transmission in the hippocampus of alert rats.

1. The effects of 5-hydroxytryptamine1 (5-HT1) ligands on excitatory synaptic transmission were examined in the stratum radiatum of the CA1 region of the dorsal hippocampus of alert, gently restrained, rats. 2. 5-HT produced a dose-dependent reduction in the amplitude of the electrically evoked population excitatory postsynaptic potential (e.p.s.p.) when injected directly into the hippocampus via a cannula (dose producing 50% maximum inhibition, ED50 = 0.46 microgram). 3. Direct intrahippocampal (i.h.) application of buspirone (ED50 = 0.29 microgram), gepirone (1 microgram), ipsapirone (1 microgram), BMY 7378 (0.1 microgram) and 5-carboxamidotryptamine (5-CT, 0.02 microgram) mimicked the inhibitory effect of 5-HT. 4. Systemic injection of buspirone (ED50 = 0.88 mg kg-1, i.p.), BMY 7378 (0.01 mg kg-1, i.p.) and RU 24969 (1 mg kg-1, s.c.) also had an inhibitory effect on the amplitude of the e.p.s.p. 5. Injection of 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 2 micrograms) and spiroxatrine (1 microgram) i.h. alone had no effect on the e.p.s.p. amplitude but prevented the inhibitory effect of 5-HT. 6. Systemic injection (i.p.) of methysergide (5 mg kg-1) and spiroxatrine (1 mg kg-1) antagonized the inhibitory effect of buspirone whereas pretreatment with ketanserin (1 mg kg-1), trifluoperazine (1 mg kg-1) and idazoxan (1 mg kg-1) had no effect on the response to buspirone. 7. It is concluded that hippocampal synaptic transmission is highly sensitive to the agonist and antagonist properties of 5-HT1 ligands in the alert rat.     

The role of 5-HT in the impairment of thermoregulation observed in rats administered MDMA (‘ecstasy’) when housed at high ambient temperature

Rationale Administration to rats of a neurotoxic dose of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) produces an impairment in thermoregulation which is reflected in a prolonged hyperthermic response to a subsequent dose of MDMA given to rats housed at high ambient temperature.Objective We wished to examine whether the impaired thermoregulation was associated with decreased cerebral 5-HT content produced by the prior neurotoxic dose of MDMA.Methods Rats were injected with drugs decreasing 5-HT function [the tryptophan hydroxlase inhibitor p-chlorophenylalanine (PCPA), and 5-HT receptor antagonists] and rectal temperature was measured after administering MDMA to rats housed at 30°C.Results PCPA pretreatment decreased 5-HT and 5-HIAA concentrations in cortex, hippocampus and striatum by >80% and prolonged the hyperthermia induced in rats housed at 30°C by administering MDMA (5 mg/kg i.p.). A similar prolongation of the hyperthermic response to MDMA was seen when rats were pretreated with methysergide (10 mg/kg i.p.) or the 5-HT_1A antagonist WAY100635 (0.5 mg/kg s.c.).Conclusions Decreasing 5-HT function in diverse ways enhanced the hyperthermic response to MDMA given to rats housed at high ambient temperature. This suggests that loss of 5-HT acting on 5-HT_1A receptors leads to impaired thermoregulation in rats and suggests that the impairment seen in MDMA pretreated rats housed at high ambient temperature is due to a loss in 5-HT function. These data could have implications for recreational users of MDMA, who may have damaged serotoninergic neurons because of prior heavy or frequent use of the drug, when taking further doses of MDMA in hot environments such as dance clubs.     

The effect of (R)-HA966 or ACEA 1021 on dexfenfluramine or (S)-MDMA-induced changes in temperature, activity, and neurotoxicity

The glycine site-specific N-methyl-D-aspartate (NMDA) antagonist 5-nitro-6,7-dichloro-2,3-quinoxalinedione (ACEA 1021, 4x30 mg/kg, i.p.) given 30 min before dexfenfluramine (4x15 mg/kg, i.p., every 2 h) was unable to prevent dexfenfluramine-induced depletion of 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA) content, and 5-HT transporter (5-HTT) density. Another glycine site-specific NMDA antagonist, R(+)-3-aminohydroxypyrrolidin-2-one [(R)-HA 966] (2x30 mg/kg, ip), given 30 min before dexfenfluramine (2x10 mg/kg, ip, 2 hourly) was also unable to prevent regional depletion of 5-HT, 5-HIAA, and 5-HTT density. However, ACEA 1021 (4x30 mg/kg, i.p.) given 30 min before (S)-3,4-methylenedioxymethamphetamine (MDMA, 4x10 mg/kg, 2 hourly, ip) attenuated the regional depletion of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), 5-HT, 5-HIAA content, and 5-HTT density. ACEA 1021 combined with (S)-MDMA also prevented (S)-MDMA-induced hyperthermia without causing hypothermia or preventing an (S)-MDMA-induced increase in locomotor activity.     

The profiles of interaction of yohimbine with anxiolytic and putative anxiolytic agents to modify 5-HT release in the frontal cortex of freely-moving rats.

1. The interaction of yohimbine with anxiolytic and putative anxiolytic agents to modify 5-hydroxytryptamine (5-HT) release in the frontal cortex of the freely-moving rat was assessed using the microdialysis technique. 2. The alpha 2-adrenoceptor antagonist, yohimbine (5.0 mg kg-1, i.p.) increased maximally the extracellular levels of 5-HT in the rat frontal cortex by approximately 230% of the basal levels. 3. The alpha 2-adrenoceptor agonist, clonidine (30-100 micrograms kg-1, i.p.) decreased dose-dependently the extracellular levels of 5-HT in the rat frontal cortex by approximately 0-60% of the basal levels. A 5 min pretreatment with clonidine (50 micrograms kg-1, i.p.) prevented the yohimbine-induced increase in the extracellular 5-HT levels. 4. The benzodiazepine receptor agonist, diazepam (2.5 mg kg-1, i.p.) and the 5-HT3 receptor antagonist, ondansetron (100 micrograms kg-1, i.p.) (5 min pretreatment) completely prevented the yohimbine (5.0 mg kg-1, i.p.)-induced increases in the extracellular levels of 5-HT. The 5-HT1A receptor agonist, 8-OH-DPAT (0.32 mg kg-1, s.c.) partially antagonized the yohimbine response. 5. A 5 min pretreatment with the 5-HT3/5-HT4 receptor ligand R(+)-zacopride (10 micrograms kg-1, i.p.) reversed the yohimbine (5.0 mg kg-1, i.p.)-induced increase in the extracellular levels of 5-HT to approximately 30% below the basal levels. A 5 min pretreatment with S(-)-zacopride (100 micrograms kg-1, i.p.) failed to modify the response to yohimbine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences between rats and mice in MDMA (methylenedioxymethylamphetamine) neurotoxicity

In both rats and mice a single large dose of methylenedioxymethylamphetamine (MDMA; 25 mg/kg i.p.) caused a fall 3 h after injection in the content of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in cortex, a fall in noradrenaline in hippocampus and cerebellum, and a rise in dopamine (DA) but fall in dihydroxyphenylacetic acid (DOPAC) in striatum. These effects were transient, levels being essentially back to normal by 24 h after injection. Repeated large doses (3 x 25 mg/kg in 24 h) of MDMA caused a large long-lasting fall in the content of 5-HT and 5-HIAA in cortex in rats but had only a slight effect in mice. Increasing the dose to 3 x 50 mg/kg in mice produced a large long-lasting fall in striatal DA. The analogue MDEA(3,4-methylenedioxyethylamphetamine) caused a similar slight fall in 5-HT but in contrast to MDMA caused a slight rise in DA content in mice. The nature and degree of neurotoxicity with methylenedioxyamphetamines appears to be drug and species-specific.     

Effect of p-chlorophenylalanine on release of 5-hydroxytryptamine from the rat frontal cortex in vivo.

1. Rats were given p-chlorophenylalanine (PCPA, 150 mg kg-1, i.p.) to inhibit partially 5-hydroxytryptamine (5-HT) synthesis so that its concentration in the frontal cortex fell by about half. The effects of this treatment on frontal cortex dialysate 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) concentrations were determined before and after stimulation by increasing K+ concentration in the perfusion fluid by 100 mM for 20 min. Rates of 5-HT synthesis as indicated by the effects of 3-hydroxybenzylhydrazine (NSD 1015, 150 mg kg-1, i.p.) on frontal cortex tissue and dialysate 5-hydroxytryptophan (5-HTP) and dialysate 5-HIAA were also measured in rats that had not been stimulated with K+. 2. Dialysate 5-HT and 5-HIAA concentrations of both vehicle- and PCPA-treated rats fell into major (group 1) and minor (group 2) populations statistically distinguishable from each other by the high 5-HT and low 5-HIAA values of the latter group. 3. In group 1 animals, PCPA decreased both the dialysate 5-HT concentration and its rise following stimulation by K+ in proportion with the decrease of 5-HT in frontal cortex tissue. 5-HIAA fell more markedly than 5-HT and in similar proportion in both tissue and dialysate. The fall of dialysate 5-HIAA on stimulation by K+ was also attenuated to the same degree. The elevated 5-HT/5-HIAA ratios after PCPA treatment imply increased conservation of the depleted 5-HT stores. 4. PCPA decreased the above 5-HIAA values and the effects of NSD 1015 on tissue 5-HTP or dialysate 5-HIAA concentrations in similar proportion.(ABSTRACT TRUNCATED AT 250 WORDS)