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Anhydroecgonine methyl ester (AEME), also called methylecgonidine, is a pyrolysis product of crack cocaine that is neurotoxic and potentiates cocaine-induced sensitization. The sensitization induced by drugs of abuse can be influenced by melatonin, a neuroprotective pineal hormone. In the same way, drugs of abuse like alcohol and methamphetamine can modify melatonin synthesis. The aim of the present work was to investigate the AEME effects on melatonin synthesis in the rat pineal gland. Neurotransmitter systems involved in its effects, antioxidant enzyme activities and the melatonin protective role in AEME-induced toxicity were also evaluated. The animals were injected with AEME i.p. (1.12 mg per kg of body weight per day) or vehicle for 10 consecutive days and the nocturnal pineal melatonin synthesis profile and SOD, GPx and GR activities in the cerebral cortex and hippocampus were assessed. Cultured pineal glands were incubated with AEME for 30 min or 48 h before norepinephrine stimulation and melatonin synthesis, arylalkylamine N-acetyltransferase activity, cAMP and [Ca2+]i were determined. The involvement of cholinergic and glutamatergic systems was analyzed using different antagonists. The protective role of melatonin in AEME toxicity on hippocampal neurons was evaluated by a viability assay. AEME impaired melatonin synthesis both in vivo and in vitro and this effect seems to be mediated by muscarinic receptors and [Ca2+]i elevation. AEME reduced neuronal viability and melatonin was able to protected hippocampal neurons against AEME toxicity. The melatonin synthesis impairment observed could lead to the worsening of the direct AEME neurotoxicity and to the exacerbation of the crack cocaine addiction and sensitization.

Smoking crack cocaine involves the inhalation of cocaine and its pyrolysis product, anhydroecgonine methyl ester (AEME). There is evidence that cocaine is neurotoxic, but the neurotoxicity of AEME has never been evaluated. AEME seems to have cholinergic agonist properties in the cardiovascular system; however, there are no reports on its effects in the central nervous system. The aim of this study was to investigate the neurotoxicity of AEME and its possible cholinergic effects in rat primary hippocampal cell cultures that were exposed to different concentrations of AEME, cocaine and to a cocaine-AEME combination. We also evaluated the involvement of muscarinic cholinergic receptors in the neuronal death induced by these treatments using concomitant incubation of the cells with atropine. Neuronal injury was assessed using 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays. The results of the viability assays showed that AEME is a neurotoxic agent that has greater neurotoxic potential than cocaine after 24 and 48 hours of exposure. We also showed that incubation for 48 hours with the combination of both compounds in equipotent concentrations had an additive neurotoxic effect. Although both substances decreased cell viability in the MTT assay, only cocaine increased LDH release. Caspase 3 activity was increased after incubation with 1 mM cocaine and after 6 hours of 0.1 and 1 mM AEME exposure. Atropine prevented the AEME-induced neurotoxicity, which suggests that muscarinic cholinergic receptors are involved in AEME's effects. In addition, binding experiments confirmed that AEME has an affinity for muscarinic cholinergic receptors. Nevertheless, atropine was not able to prevent the neurotoxicity produced by cocaine and the cocaine-AEME combination, suggesting that these treatments activated other neuronal death pathways. Our results suggest a higher risk for neurotoxicity after smoking crack cocaine than after cocaine use alone. Language: en