Effect of Aripiprazole on Methamphetamine-Induced Disruption of Latent Inhibition in Rats

Objectives: To elucidate the pharmacological profile of aripiprazole, we examined its ameliorating effect on the methamphetamine-induced disruption of latent inhibition (LI) in rats. Method: The effect was measured using a conditioned emotional response procedure. The conditioned stimulus was a tone (2.8 kHz, 90 dB), and the unconditioned stimulus was a mild foot shock delivered through a floor grid. The conditioning procedure was repeated five times. Results: Methamphetamine-induced (1.0 mg/kg, i.p.) disruption of LI was ameliorated by the administration of haloperidol (0.2 mg/kg, i.p.) and by a moderate dose of aripiprazole (0.3 mg/kg, i.p.) but not by a lower or higher dose (0.1 or 3.0 mg/kg, i.p.) of aripiprazole. However, immunohistochemical examination showed increased levels of c-Fos expression in the shell of the nucleus accumbens after the administration of haloperidol (0.2 mg/kg, i.p.) but not of aripiprazole (0.3 mg/kg, i.p.). Conclusions: It is suggested that aripiprazole has an ameliorating effect on methamphetamine-induced disruption of latent inhibition within only a marginal therapeutic window.