Damage to dopaminergic nerve terminals in mice by combined treatment of intrastriatal malonate with systemic methamphetamine or MPTP.

The mechanisms involved in methamphetamine (METH)-induced damage to nigrostriatal dopaminergic neurons in experimental animals are unknown. We have examined the possibility that perturbations in energy metabolism contribute to METH-induced toxicity by investigating the effects of systemic METH treatment in mice which received a unilateral intrastriatal infusion of malonate, a metabolic inhibitor which decreases ATP levels. Malonate (1-4 mumol) produced a dose-dependent decrease in striatal dopamine (DA). The combined treatment of intrastriatal malonate with systemic METH resulted in greater damage to dopaminergic neurons than by METH or malonate treatment alone. In parallel studies, MPTP was administered to mice which received intrastriatal infusions of saline or malonate. Similar to results obtained with METH, decreases in striatal DA content and tyrosine hydroxylase (TH) activity were greatest in MPTP-treated mice infused with malonate. The present results lend credence to the hypothesis that METH-induced increases in energy utilization create a state of metabolic stress for DA neurons which may ultimately contribute to the neurodegenerative effects of METH. Moreover, the finding that combined malonate and MPTP treatment produced greater damage than either substance alone is consistent with the hypothesis that perturbations in energy metabolism contribute to the neuronal death produced by MPP+.