Behavioural and neurochemical effects of combined MDMA and THC administration in mice

Rationale Cannabis is the most widely consumed drug associated with 3,4-methylenedioxymethamphetamine (MDMA) use. Objectives This study examines whether low doses of MDMA and delta-9-tetrahydrocannabinol (THC) produce synergistic rewarding/reinforcing effects in mice using the conditioned place preference (CPP) and operant self-administration paradigms. Changes in dopamine (DA) outflow were monitored in the nucleus accumbens (NAC) after single or combined administration of these compounds. Results MDMA induced a significant CPP at the dose of 10 mg/kg but not at the dose of 3 mg/kg. THC (0.3 mg/kg) by itself was also ineffective in this paradigm. The combined administration of the low dose of MDMA (3 mg/kg) and THC (0.3 mg/kg) produced CPP, whereas the combination of MDMA (10 mg/kg) and THC (0.3 mg/kg) significantly decreased CPP. Animals treated with THC self-administered a sub-threshold dose of MDMA (0.06 mg/kg per infusion), while animals receiving vehicle did not. However, THC did not modify the self-administration of an effective dose of MDMA (0.125 mg/kg per infusion). In microdialysis studies, a low dose of THC significantly increased DA outflow in the NAC, while a low dose of MDMA did not. When MDMA was administered before THC, DA levels decreased with respect to THC. However, when THC was administered before MDMA, DA levels were not significantly modified with respect to THC. Conclusions These results demonstrate that a low dose of THC modifies in different ways (increases and decreases) the sensitivity of animals to the behavioural effects of MDMA and that THC and MDMA converge at a common mechanism modulating DA outflow in the NAC of mice.     

A neurotoxic regimen of MDMA suppresses behavioral, thermal and neurochemical responses to subsequent MDMA administration

Rationale: 3,4-Methylenedioxymethamphetamine (MDMA) produces a long-term depletion of serotonin (5-HT) in the rat brain; this depletion may have some functional consequences. Objective: The aim of the present study was to evaluate the acute effects of MDMA on the extracellular concentrations of dopamine and 5-HT, body temperature and the 5-HT behavioral syndrome in rats 7 days following a neurotoxic regimen of MDMA. Methods: One week after the rats were treated with a neurotoxic regimen of MDMA (10 mg/kg, IP, every 2 h for a total of four injections), the rats were injected with a subsequent injection of MDMA. In vivo microdialysis combined with HPLC was utilized to measure the extracellular concentration of 5-HT and dopamine in the striatum. The increase in body temperature was determined by rectal temperature measurements, and the 5-HT behavioral syndrome was scored using a rating scale following the administration of MDMA.Results: The neurotoxic regimen produced a 45% reduction in brain 5-HT concentrations. The magnitude of the MDMA-induced increase in the extracellular concentration of 5-HT, but not dopamine, in the striatum produced by an acute injection of MDMA (7.5 mg/kg, IP) was reduced in rats treated previously with the neurotoxic regimen of MDMA when compared with that in control animals. In addition, the magnitude of the 5-HT behavioral syndrome, as well as the hyperthermic response, produced by MDMA was markedly diminished in rats that had previously received the neurotoxic regimen of MDMA. Conclusions: It is concluded that the long-term depletion of brain 5-HT produced by MDMA is accompanied by impairments in 5-HT function, as evidenced by the deficits in the neurochemical, thermal and behavioral responses to subsequent MDMA administration. Received: 1 March 1999 / Final version: 1 June 1999     

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     

Comparative neuropharmacology of three psychostimulant cathinone derivatives: butylone, mephedrone and methylone

BACKGROUND AND PURPOSE

Here, we have compared the neurochemical profile of three new cathinones, butylone, mephedrone and methylone, in terms of their potential to inhibit plasmalemmal and vesicular monoamine transporters. Their interaction with 5-HT and dopamine receptors and their psychostimulant effect was also studied.

EXPERIMENTAL APPROACH

Locomotor activity was recorded in mice following different doses of cathinones. Monoamine uptake assays were performed in purified rat synaptosomes. Radioligand-binding assays were carried out to assess the affinity of these compounds for monoamine transporters or receptors.

KEY RESULTS

Butylone, mephedrone and methylone (5–25 mg·kg⁻¹) caused hyperlocomotion, which was prevented with ketanserin or haloperidol. Methylone was the most potent compound inhibiting both [³H]5-HT and [³H]dopamine uptake with IC₅₀ values that correlate with its affinity for dopamine and 5-HT transporter. Mephedrone was found to be the cathinone derivative with highest affinity for vesicular monoamine transporter-2 causing the inhibition of dopamine uptake. The affinity of cathinones for 5-HT_2A receptors was similar to that of MDMA.

CONCLUSIONS AND IMPLICATIONS

Butylone and methylone induced hyperlocomotion through activating 5-HT_2A receptors and increasing extra-cellular dopamine. They inhibited 5-HT and dopamine uptake by competing with substrate. Methylone was the most potent 5-HT and dopamine uptake inhibitor and its effect partly persisted after withdrawal. Mephedrone-induced hyperlocomotion was dependent on endogenous 5-HT. Vesicular content played a key role in the effect of mephedrone, especially for 5-HT uptake inhibition. The potency of mephedrone in inhibiting noradrenaline uptake suggests a sympathetic effect of this cathinone.     

The pharmacology and toxicology of the synthetic cathinone mephedrone (4-methylmethcathinone)

Mephedrone (4-methylmethcathinone) is a synthetic cathinone that is used as a recreational drug. It has been available since 2007 but its availability and use increased significantly during 2009 and 2010. In this review article we will summarize the available literature on the sources, availability, and prevalence of the use of mephedrone. We will also discuss the pharmacology of mephedrone, the patterns of acute toxicity associated with its use, the reports of fatalities associated with its use, and the potential for mephedrone dependence.     

Behavioural effects of long-term administration of fencamfamine: neurochemical implications

The repeated effects of fencamfamine administration (10.0 mg/kg, i.p. single dose) were studied in male rats. Fencamfamine treatment increased stereotyped sniffing and decreased rearing behaviour. These changes occurred after 8 days of treatment and remained for 25 days. The fencamfamine repeated administration enhanced the homovanillic acid (HVA) level in the tubercullum olfactorium while the same treatment decreased the dihydroxyphenilacetic acid (DOPAC) and HVA striatal levels. The data suggest that long-term fencamfamine administration develops changes in the activity of parts of the DA systems which might be responsible for tolerance or sensitization to the effects of fencamfamine.     

Behavioural and neurochemical effects of repeated administration of cocaine in rats.

The effects of repeated administration of cocaine (15 mg/kg, i.p. twice daily at 8-hr intervals) were investigated on the spontaneous motor activity (SMA) and stereotypy (ST) as well as on the various neurotransmitters (e.g. norepinephrine, NE; dopamine, DA; serotonin, 5-HT; acetylcholine, ACh) in different brain areas (e.g. diencephalon-midbrain, DM; pons-medulla, PM; caudate nucleus, CN) in rats.Following repeated injections of cocaine, both SMA and ST gradually increased, reaching a peak in each case on about the 9th day, then gradually decreased up to the 18th or 20th day, after which the activities were maintained at minimum level which was slightly higher than normal levels. Concomitantly, the DA level in the CN and DM increased and 5-HT in the DM and PM decreased reaching their maximum or minimum levels following cocaine injections on the 9th day; these changes were gradually minimized by the 18th day and remained so up to the 30th day. There were also slight changes in NE and ACh levels. It thus appears that, following repeated cocaine administrations, the changes in the drug-induced behavioural effects can be correlated roughly with the changes in the DA level in the CN and the 5-HT levels in the DM and PM.     

Cannabinoids: neurochemical aspects after oral chronic administration to rats

Male and female Fischer rats were treated orally with Δ⁹-THC doses between 50 and 500 mg/kg or with crude marihuana extract between 50 and 1500 mg/kg, for 28 or 91 consecutive days. At necropsy, brains were weighed and kept frozen until 10% homogenates in 0.32 m sucrose could be made and analyzed. Homogenate samples were assayed for total protein, RNA, lipids, and acetylcholinesterase, succinic dehydrogenase and monoamine oxidase activities. Significant decreases were obtained for protein, RNA and acetylcholinesterase activity at 28 days and monoamine oxidase at 91 days. No changes in total lipids, glycolipids or cholesterol concentrations were observed. The neurochemical alterations coincided with behavioral symptoms of hyperactivity and convulsive activity. Both neurotoxicity and neurochemical changes were partially reversed after the longer interval of treatment.     

3,4‐methylenedioxymethamphetamine (MDMA; Ecstasy) administration produces dose‐dependent neurochemical,endocrine and immune changes in the rat

3,4‐methylenedioxymethamphetamine (MDMA, Ecstasy) is a widely abused drug that is structurally related to both amphetamines and hallucinogens. In addition to the behavioural and neurochemical effects of MDMA, we recently reported that an acute administration of this drug produces a profound suppression of mitogen‐stimulated lymphocyte proliferation and reduction in the number of circulating white blood cells, which was accompanied by elevated circulating corticosterone concentrations. In the present study, the effect of acute MDMA administration on PHA‐induced lymphocyte proliferation, leucocyte subpopulations, HPA‐axis activity and cortical serotonin utilization were examined in a dose‐dependent manner in female Sprague‐Dawley rats. The results of this study demonstrate that MDMA induces a suppression of lymphocyte function even at doses that fail to provoke any significant alteration in central 5‐HT utilization and plasma corticosterone concentrations, thereby suggesting that the reduced functional responsiveness of lymphocytes to mitogenic stimulation after MDMA administration may be mediated by glucocorticoid independent mechanisms. In contrast, the MDMA‐induced reduction in the number of circulating blood lymphocytes was evident only at doses of MDMA which elevated circulating corticosterone concentrations, suggesting that the observed reduction in circulating lymphocytes may be at least partly a glucocorticoid‐mediated event. Copyright © 1999 John Wiley & Sons, Ltd.     

Behavioral and neurochemical effects induced by chronic L-DOPA administration

L-DOPA, in combination with benserazide, in the ratio 4:1 (w/w), was administered orally to rats. In the staircase maze test a low dose of L-DOPA (3 mg/kg/day) reduced the increase in errors caused by 20 days interruption of daily training, while a higher dose (30 mg/kg/day) was ineffective. A decrease in levels of dopamine in the olfactory system and DOPAC in the striatum was seen at all tested doses of L-DOPA, while an increase in 5-HT levels was seen in the hippocampus and in the striatum. 5-HIAA levels did not change. Levels of ACh in the olfactory system were reduced at all doses of L-DOPA, while in the hippocampus this effect was seen only at the dose of 90 mg/kg/day. The density of muscarinic receptors was not altered. AI1 tested doses of L-DOPA caused norepinephrine levels to fall in the hippocampus and increase in the striatum. The density of α₁-adrenoceptors was reduced only at the two lower doses of L-DOPA. A comparison of the neurochemical results with the behavioral modifications seen in the staircase maze test suggests that the catecolaminergic systems are implicated in the memory process.     

Behavioral and neurochemical modifications caused by chronic alpha-methylparatyrosine administration.

The chronic administration of alpha-methylparatyrosine (AMT) caused a reduction of the noradrenaline levels in the hippocampus (at 150 and 300 mg/kg/day) and in the subcortex (at 30, 150 and 300 mg/kg/day). The acetylcholine levels were reduced in the hippocampus and in the olfactory brain at all the tested doses of AMT. An increase of the Bmax of muscarinic and alpha 1-adrenoceptors was observed at 30 mg/kg/day of AMT; only in the subcortex AMT caused no modification of the density of muscarinic receptors. The degree of increase of the receptors density at 30 mg/kg/day was reduced at the higher doses of AMT. AMT 30 mg/kg/day caused a reduction of the errors in the staircase maze after 20 days of interruption of the daily training. These results might suggest a correlation between the behavioral effect and the increase of density, not only of the adrenoceptors, but also of the muscarinic receptors. It is proposed that the behavioral effects caused by chronic AMT are the consequence of complex neurochemical interactions.     

Stereochemistry of mephedrone neuropharmacology: enantiomer-specific behavioural and neurochemical effects in rats

Background and Purpose

Synthetic cathinones, commonly referred to as ‘bath salts’, are a group of amphetamine-like drugs gaining popularity worldwide. 4-Methylmethcathinone (mephedrone, MEPH) is the most commonly abused synthetic cathinone in the UK, and exerts its effects by acting as a substrate-type releaser at monoamine transporters. Similar to other cathinone-related compounds, MEPH has a chiral centre and exists stably as two enantiomers: R-mephedrone (R-MEPH) and S-mephedrone (S-MEPH).

Experimental Approach

Here, we provide the first investigation into the neurochemical and behavioural effects of R-MEPH and S-MEPH. We analysed both enantiomers in rat brain synaptosome neurotransmitter release assays and also investigated their effects on locomotor activity (e.g. ambulatory activity and repetitive movements), behavioural sensitization and reward.

Key Results

Both enantiomers displayed similar potency as substrates (i.e. releasers) at dopamine transporters, but R-MEPH was much less potent than S-MEPH as a substrate at 5-HT transporters. Locomotor activity was evaluated in acute and repeated administration paradigms, with R-MEPH producing greater repetitive movements than S-MEPH across multiple doses. After repeated drug exposure, only R-MEPH produced sensitization of repetitive movements. R-MEPH produced a conditioned place preference whereas S-MEPH did not. Lastly, R-MEPH and S-MEPH produced biphasic profiles in an assay of intracranial self-stimulation (ICSS), but R-MEPH produced greater ICSS facilitation than S-MEPH.

Conclusions and Implications

Our data are the first to demonstrate stereospecific effects of MEPH enantiomers and suggest that the predominant dopaminergic actions of R-MEPH (i.e. the lack of serotonergic actions) render this stereoisomer more stimulant-like when compared with S-MEPH. This hypothesis warrants further study.     

Chronic administration of THC prevents the behavioral effects of intermittent adolescent MDMA administration and attenuates MDMA-induced hyperthermia and neurotoxicity in rats

Most recreational users of 3, 4-methylenedioxymethamphetamine (MDMA or “ecstasy”) also take cannabis, in part because cannabis can reduce the dysphoric symptoms of the ecstasy come-down such as agitation and insomnia. Although previous animal studies have examined the acute effects of co-administering MDMA and Δ⁹-tetrahydrocannabinol (THC), which is the major psychoactive ingredient in cannabis, research on chronic exposure to this drug combination is lacking. Therefore, the present study was conducted to investigate the effects of chronic adolescent administration of both THC and MDMA on behavior and on regional serotonin transporter (SERT) binding and serotonin (5-HT) concentrations as indices of serotonergic system integrity. Male Sprague-Dawley rats were divided into four drug administration groups: (1) MDMA alone, (2) THC alone, (3) MDMA plus THC, and (4) vehicle controls. MDMA (2 × 10 mg/kg × 4 h) was administered every fifth day from postnatal day (PD) 35 to 60 to simulate intermittent recreational ecstasy use, whereas THC (5 mg/kg) was given once daily over the same time period to simulate heavy cannabis use. THC unexpectedly produced a modest hyperthermic effect when administered alone, but in animals co-treated with both THC and MDMA, there was an attenuation of MDMA-induced hyperthermia on dosing days. Subsequent testing conducted after a drug washout period revealed that THC reduced MDMA-related behavioral changes in the emergence and social interaction tests of anxiety-like behavior and also blunted the MDMA-induced decrease in exploratory behavior in the hole-board test. THC additionally attenuated MDMA -induced decreases in 5-HT levels and in SERT binding in the frontal cortex, parietal cortex, and striatum, but not in the hippocampus. These results suggest that chronic co-administration of THC during adolescence can provide some protection against various adverse physiological, behavioral, and neurochemical effects produced by MDMA.     

Behavioural and neurochemical effects of medetomidine, a novel veterinary sedative

The effects of the novel veterinary sedative, medetomidine, were studied in rats. In addition to a dose-dependent sedation, which at high doses (greater than 100 micrograms/kg) included loss of the righting reflex and hypothermia, there was a concurrent decrease in the turnover rate of biogenic amines in the brain. Noradrenaline turnover was dose dependently decreased as judged by (i) the decrease in the brain concentration of its metabolite, MHPG-SO4, (ii) a decrease in the ability of alpha-methyl-p-tyrosine methyl ester to deplete brain noradrenaline stores and (iii) a dose-dependent decrease in the level of unconjugated MHPG in the CSF of freely moving rats. Brain dopamine turnover was also inhibited at higher doses as judged by the alpha-methyl-p-tyrosine method and by a decrease in the concentration of HVA in the rat brain 4 h after medetomidine. Serotonin turnover as estimated by the ratio of biogenic amine to its metabolite was also significantly depressed. These changes in brain biogenic amine turnover were inhibited by prior or simultaneous administration of alpha 2-adrenoceptor antagonists, either yohimbine or the more specific, novel alpha 2-antagonist, atipamezole.     

Behavioural and neurochemical interactions between chronic reserpine and chronic antidepressants. A possible model for the detection of atypical antidepressants

Chronic treatment with a low dose of reserpine (0.1 mg/kg) caused rats to become hyperactive in the "open field" apparatus. When mianserin (5 mg/kg) or the selective serotonin uptake inhibitor ORG. 6582 (5 mg/kg) was chronically administered in combination with reserpine, the hyperactivity was attenuated. Both antidepressants were found to reverse the reduction in the noradrenaline concentration of the amygdaloid cortex caused by chronic reserpine treatment. It is proposed that changes in the activity of the noradrenergic system in the amygdaloid cortex may be causally related to the changes in activity of the rats in the "open field" apparatus.     

Behavioural effects of acute and chronic β-phenylethylamine administration in the rat: Evidence for the involvement of 5-hydroxytryptamine

The behavioural consequences of daily β-phenylethylamine (PEA) administration for a period of 6 weeks have been examined. Rats first showed signs of the 5-HT behavioural syndrome after a single injection of PEA (50 mg/kg) or 7 daily injections of PEA (25 mg/kg). The syndrome reached peak intensity after 3 weeks treatment and was prevented by pre-treatment with the 5-HT antagonists mianserin and methysergide or the neuroleptic clozapine, but relatively unaffected by pre-treatment with haloperidol. These data provide strong evidence for an effect of PEA on brain 5-HT mechanisms. Because of the similarity between PEA and amphetamine and the suggestion that PEA may be involved in the aetiology of schizophrenia it is proposed that the mechanisms of action of PEA be reassessed taking into account its ability to affect 5-HT systems in addition to catecholaminergic systems.     

Baclofen and muscimol: Behavioural and neurochemical sequelae of unilateral intranigral administration and effects on 3H-GABA receptor binding

Summary Log dose-response curves for induction of contralateral rotational behaviour in the rat by unilateral intranigral injections of the GABA agonist muscimol and the GABA analogue baclofen have been compared. Baclofen, 5–1000 ng, produced a maximal rotational response that was only 40% of that produced by 0.25–100 ng muscimol, and log dose-response curves failed to show parallelism. The behavioural effects of both drugs were only weakly antagonised by haloperidol and were not antagonised by 6-hydroxydopamine lesions of ipsilateral dopamine (DA) neurons, indicating that these responses were independent of DAergic mechanisms. The effects of baclofen were weakly antagonised by picrotoxin. Intranigral muscimol and baclofen substantially elevated striatal DA concentrations. While muscimol also substantially elevated striatal dihydroxyphenylacetic acid (DOPAC) but not homovanillic acid (HVA), baclofen did not significantly effect either DOPAC or HVA. Baclofen, GABA and muscimol displaced specific ³H-GABA binding in vitro with IC₅₀'s of 40 m 400 nM and 40 nM respectively. These results indicate that muscimol and baclofen do not act via a unitary GABAergic mechanism, but suggest that baclofen may be a partial GABA agonist, at least at nigral GABA receptors.     

Quantitative mapping shows that serotonin rather than dopamine receptor mRNA expressions are affected after repeated intermittent administration of MDMA in rat brain

Ecstasy, (+/-)-3,4-methylenedioxy-metamphetamine (MDMA), is a popular recreational drug among young people. The present study aims to mimic MDMA intake among adolescents at dance clubs, taking repeated doses in the same evening on an intermittent basis. Male Sprague-Dawley rats received either 3x1 or 3x5 mg/kg/day (3 h apart) every seventh day during 4 weeks. We used real-time RT-PCR to determine the gene expression of serotonin 5HT1A, 5HT1B, 5HT2A, 5HT2C, 5HT3, 5HT6 receptors and dopamine D1, D2, D3 receptors in seven brain nuclei. The highest dose of MDMA extensively increased the 5HT1B-receptor mRNA in the cortex, caudate putamen, nucleus accumbens, and hypothalamus. The 5HT2A-receptor mRNA was reduced at the highest MDMA dose in the cortex. The 5HT2C mRNA was significantly increased in a dose-dependent manner in the cortex and the hypothalamus, as well as the 5HT3-receptor mRNA was in the hypothalamus. The 5HT6 mRNA level was increased in the forebrain cortex and the amygdala. Dopamine receptor mRNAs were only affected in the hypothalamus. In conclusion, this study provides evidence for a unique implication of serotonin rather than dopamine receptor mRNA levels, in response to repeated intermittent MDMA administration. We therefore suggest that serotonin regulated functions also primarily underlie repeated MDMA intake at rave parties.