Involvement of adenosine receptors in the induction of c-fos expression by clozapine and haloperidol

Acute administration of the atypical antipsychotic clozapine induced a regional pattern of c-fos expression characterized by an increase in Fos-like-immunoreactivity (FLI) in the prefrontal and prelimbic/infralimbic cortices, nucleus accumbens, and lateral septum and a weak activation of FLI in the striatum. Haloperidol, similarly to clozapine, increased FLI in the nucleus accumbens and lateral septum, but it did not induce FLI in prefrontal and prelimbic/infralimbic cortices. Moreover, haloperidol increased FLI in the striatum. To gain insight into the mechanism by which clozapine and haloperidol induced FLI in these brain structures, we evaluated whether blockade of adenosine A2A receptors could influence these effects. The selective and high-affinity A2A receptor antagonist SCH 58261 (5 mg/kg) completely abolished FLI induced by clozapine (20 mg/kg) in all subdivisions of the nucleus accumbens (rostral pole, shell and core) and striatum, but did not affect the number of Fos-like positive neurons in the prefrontal, prelimbic/infralimbic cortices, and lateral septum. SCH 58261 (5 mg/kg) reduced FLI induced by haloperidol (0.1 mg/kg) in the striatum, lateral septum, and all nucleus accumbens subdivisions. In contrast, FLI induced by 0.5 mg/kg of haloperidol in the shell and core of the nucleus accumbens was not affected by SCH 58261. The results show that adenosine A2A receptors participate in the induction of FLI by clozapine and haloperidol and support the concept that A2A receptors are involved in the mediation of antipsychotic effects.