Dose-dependent protective effects of apomorphine against methamphetamine-induced nigrostriatal damage

(R)-apomorphine is a non-selective dopamine (DA) agonist which is used in the treatment of Parkinson's disease. In addition to symptomatic effects, apomorphine exerts a neuroprotective activity in specific experimental models. For instance, apomorphine prevents experimental parkinsonism induced by the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Neuroprotection obtained with apomorphine does not seem to be related to its dopamine (DA) agonist properties, instead it appears to be grounded on the antioxidant and the free radical scavenging effects of the compound. In this study, we sought to determine whether apomorphine protects against methamphetamine toxicity. We found that apomorphine (1; 5 and 10 mg/kg) dose-dependently protects against methamphetamine- (5 mg/kg X3, 2 h apart) induced striatal DA loss and reduction of tyrosine hydroxylase (TH) activity in the rat striatum. These protective effects are neither due to a decrease in the amount of striatal methamphetamine nor to hypothermia as indicated by measurement of striatal methamphetamine and body temperature at different time intervals after drug administration. The effects of apomorphine were neither opposite to, nor reversed by the DA antagonist haloperidol despite no decrease in body temperature was observed when apomorphine was given in combination with haloperidol. The present data are in line with recent studies suggesting a DA receptor-independent neuroprotective effect of apomorphine on DA neurons and call for further studies aimed at evaluating potential neuroprotective effects of apomorphine in Parkinson's disease.