Role of the dorsal raphe nucleus in morphine-induced immediate early gene expression in the rat striatum

Abstract

Serotonin (5-HT) is thought to be involved in morphine action in the brain. To determine if the periaqueductal gray (PAG) and the dorsal raphe nucleus (DRN) are involved in morphine-induced c-Fos and JunB expression in the caudate–putamen (CPu), the μ receptor antagonist, β-funaltrexamine (β-FNA), was unilaterally infused into the PAG adjacent to DRN prior to morphine. Behaviorally, β-FNA prevented morphine-induced loss of righting and Straub tail. In the CPu of β-FNA treated rats, morphine-induced c-Fos and JunB were attenuated compared to vehicle-infused rats. These results suggest that morphine acts within the PAG–DRN to exert rapid behavioral effects and to induce c-Fos and JunB in the striatum.