Studies on the antagonism by raphe lesions of the antinociceptive action of systemic morphine.
In rats, lesions were placed in the dorsal/median raphe (DMR), in the ventral raphe (VR: raphe magnus), in both the dorsal/median and ventral raphe (DMVR) or in the reticular formation (RF). The effect of the lesions on the antinociception and catalepsy produced by 3 doses of morphine (3, 10 and 30 mg/kg) was examined. The lesions had no significant effect on the catalepsy produced by any of the doses of morphine tested. DMR lesions produced a partial attentuation of the antinociceptive action of both the 3 and 10 mg doses. VR lesions produced a complete blockade of the 3 mg and only a partial attenuation of the 10 mg dose. In contrast, the combined (DMVR) lesions yielded virtually a total blockade of the 3 and 10 mg. Yet, as with the DMR and VR groups, the DMVR lesions failed to produce a significant antagonism on either of the nociceptive tests at the 30 mg dose. These findings suggest that the ascending and descending fiber systems emanating from the dorsal/median and ventral raphe, respectively, facilitate the expression of morphine-induced analgesia but that neither system alone can be regarded as essential for the manifestation of the antinociceptive effects of systematically administered morphine.
Studies on the antagonism by raphe lesions of the antinociceptive action of systemic morphine. In rats, lesions were placed in the dorsal/median raphe (DMR), in the ventral raphe (VR: raphe magnus), in both the dorsal/median and ventral raphe (DMVR) or in the reticular formation (RF). The effect of the lesions on the antinociception and catalepsy produced by 3 doses of morphine (3, 10 and 30 mg/kg) was examined. The lesions had no significant effect on the catalepsy produced by any of the doses of morphine tested. DMR lesions produced a partial attentuation of the antinociceptive action of both the 3 and 10 mg doses. VR lesions produced a complete blockade of the 3 mg and only a partial attenuation of the 10 mg dose. In contrast, the combined (DMVR) lesions yielded virtually a total blockade of the 3 and 10 mg. Yet, as with the DMR and VR groups, the DMVR lesions failed to produce a significant antagonism on either of the nociceptive tests at the 30 mg dose. These findings suggest that the ascending and descending fiber systems emanating from the dorsal/median and ventral raphe, respectively, facilitate the expression of morphine-induced analgesia but that neither system alone can be regarded as essential for the manifestation of the antinociceptive effects of systematically administered morphine.