We examined changes in nuclear peroxisome proliferator-activated receptor gamma (PPAR gamma) in the striatum in methamphetamine (METH)-induced dopaminergic neurotoxicity, and also examined effects of treatment with drugs possessing PPAR gamma agonistic properties. The marked reduction of nuclear PPAR gamma-expressed cells was seen in the striatum 3 days after METH injections (4 mg/kg x 4, i.p. with 2-h interval). The reduction of dopamine transporter (DAT)-positive signals and PPAR gamma expression, and accumulation of activated microglial cells were significantly and dose-dependently attenuated by four injections of a nonsteroidal anti-inflammatory drug and a PPAR gamma ligand, ibuprofen (10 or 20 mg/kg x 4, s.c.) given 30 min prior to each METH injection, but not by either a low or high dose of aspirin. Either treatment of ibuprofen or aspirin, that showed no effects on METH-induced hyperthermia, significantly blocked the METH-induced striatal cyclooxygenase (COX) expression. Furthermore, the treatment of an intrinsic PPAR gamma ligand 15d-PG J2 also attenuated METH injections-induced reduction of striatal DAT. Therefore, the present study suggests the involvement of reduction of PPAR gamma expression in METH-induced neurotoxicity. Taken together with the previous report showing protective effects of other PPAR gamma ligand, these results imply that the protective effects of ibuprofen against METH-induced neurotoxicity may be based, in part, on its anti-inflammatory PPAR gamma agonistic properties, but not on its COX-inhibiting property or hypothermic effect.