Peroxisome Proliferator-Activated Receptor Gamma Activation Relieves Expression of Behavioral Sensitization to Methamphetamine in Mice

Peroxisome proliferator-activated receptor (PPAR) is a ligand-activated transcriptional factor that regulates lipid metabolism and inflammation. Behavioral sensitization is an experimental model of psychostimulant psychosis; it is elicited by repeated administration of psychostimulants and has recently been implicated in brain inflammation. We examined the involvement of PPAR γ , one of the isotypes of PPAR, in development of behavioral sensitization to the stimulant effect of methamphetamine (METH) (1 mg/kg, subcutaneously) in mice. Repeated administration of METH (once daily for 5 days) enhanced the locomotor-activating effect of METH, which was reproduced by METH challenge on withdrawal day 7 (test day 12). The protein level and the activity of PPAR γ were significantly increased in the nuclear fraction of whole brain after 5 days of METH administration (test day 5) and on withdrawal day 7 (test day 12). Both pioglitazone and ciglitazone (PPAR γ agonists; 0.5–5.0 μg, intracerebroventricularly (i.c.v.), once daily) prevented the expression of behavioral sensitization to METH challenge on withdrawal day 7, but not the sensitization that occurred during repeated administration of METH. In addition, the magnitude of expression of behavioral sensitization was augmented by treatments with GW9662 (a PPAR γ antagonist; 0.5–5.0 μg i.c.v., once daily) during the withdrawal period. The pioglitazone-induced alleviation of behavioral sensitization was synergistically facilitated by simultaneous i.c.v. injection of 9- cis -retinoic acid (1.0 μg), an agonist for the retinoid X receptor which is a ligand-activated nuclear receptor that forms heterodimers with PPAR. These results suggest that PPAR γ has a significant role in the expression of behavioral sensitization to METH in mice.