RESUMO
Estrogen potentiates behavioral sensitization to cocaine in the female rat by mechanisms that remain undetermined. In this study, functional receptor autoradiography was used to investigate estrogen modulation of D2/D3 receptor-induced G protein activation in components of the reward pathway of female rats treated acutely and repeatedly with cocaine. Rats were ovariectomized and given an empty (OVX group) or estradiol benzoate-filled (OVX-EB group) implant. After a week, animals received a daily saline or cocaine injection (15 mg/kg, i.p.) for 5 days, and again on day 13. Animals were killed, and brains were removed and cryosectioned. D2/D3-stimulated [35S]guanosine 5'-(gamma-thio) triphosphate (GTPgammaS) binding was assessed in the cingulate cortex area 2 (Cg2), striatum (STR), nucleus accumbens (NAc) and ventral tegmental area (VTA). OVX-EB rats showed more [35S]GTPgammaS binding in the Cg2 and lower binding in the VTA than OVX rats; in the VTA this effect was reversed by a single cocaine injection. Repeated cocaine administration had opposite effects in OVX and OVX-EB rats. [35S]GTPgammaS binding was decreased in the Cg2, NAc and STR of OVX-EB rats, and increased in OVX rats. The present results support the hypothesis that cocaine-induced changes in D2/D3 receptor activation are regulated by estrogen. These data suggest that changes in D2/D3 receptor function represent one mechanism by which estrogen regulates behavioral sensitization to cocaine.