Novel effects of MPTP: MAO-B unrelated opioidergic activity in mice

The presence of opioidergic activity after i.p. injection of N-methyl-4-phenyl tetrahydropyridine (MPTP) has been investigated in albino mice by studying analgesia and the Straub reaction. MPTP (6.25-25 mg kg-1) produced a dose-related analgesic response and Straub reaction. These effects of MPTP were effectively antagonized by prior naloxone treatment but remained unaffected after the MAO-B inhibitor deprenyl. MPTP thus possesses significant opioidergic activity and this, unlike its neurotoxic actions, does not appear to be dependent on oxidative conversion to MPP+ (1-methyl-4-phenyl pyridinium).