Participation of the nucleus reticularis gigantocellularis in the morphine-induced elevation of plasma corticosterone in rats.

The effects of morphine, adrenocorticotropic hormone (ACTH) and formalin on plasma corticosterone levels were investigated in the nucleus reticularis gigantocellularis (NRGC)-lesioned rats. ACTH (1.0 U/kg) or formalin (6.4%, 0.2 ml/rat) elevated plasma corticosterone in both sham-lesioned and NRGC-lesioned rats at the same degree, while morphine (10 mg/kg) also elevated plasma corticosterone in sham-lesioned rats, the elevation of which was significantly reduced by NRGC-lesioning. These findings suggest that the NRGC is involved in the corticosterone-increasing effect of morphine, but not involved in the effect of ACTH or formalin.