Methamphetamine and MDMA neurotoxicity: Biochemical and molecular mechanisms

Abstract

Methamphetamine (METH) and its analogs, methylenedioxymethamphetamine (MDMA), are psychostimulant drugs with high abuse liability. The two drugs are also very neurotoxic. In the case of METH, the behavioral and neurotoxic effects of the drug occur because it alters dopamine terminal physiology and causes massive release of dopamine (DA) in the synaptic cleft in brain regions that receive dopaminergic projections from the midbrain. The increase of synaptic DA is compounded by the ability of METH to block DA reuptake into DA terminals. METH toxicity is not only accompanied by terminal dysfunction but also by causing dysfunction of complex networks that subserve cognitive and emotional processes. MDMA is a ring-substituted derivative of phenylisopropylamine which is structurally similar to METH. MDMA is a substrate of the serotonin transporter (SERT) via which it enters monoaminergic neurons and causes release of serotonin (5-HT) from storage vesicles. This is followed by 5-HT release into the synaptic cleft by reversal of normal SERT function. MDMA is selectively neurotoxic to serotonergic nerve terminals in rats, Guinea pigs, and nonhuman primates. MDMA users consistently show reduced SERT radionuclide ligand binding across multiple brain regions. There is also evidence that MDMA users can suffer from cognitive deficits. However, the relation of DA and/or 5-HT depletion to cognitive impairments remains to be clarified in METH and MDMA users. Results from these studies are likely to impact the therapeutic approaches to the treatment of patients who suffer from METH and MDMA addiction.