Selective mediation of kappa-opioid central cardiovascular effects by ascending noradrenergic pathways.

The role of ascending noradrenergic pathways in the mediation of central opiate-induced cardiovascular effects has been investigated. The effects of selective kappa- and delta-opiate agonists microinjected into the nucleus tractus solitarius (NTS) of urethane anaesthetized rats were compared following 6-hydroxydopamine lesions of either the dorsal (DNAB) or ventral (VNAB) noradrenergic bundles. In sham lesioned animals both opiates elicited a significant pressor effect and a variable but consistent bradycardia. The delta-agonist responses were not modified in lesioned rats. In marked contrast the pressor effect of the kappa-agonist was abolished in both DNAB and VNAB lesioned rats. The bradycardic response was not significantly modified. These findings are consistent with previous observations that the cardiovascular effects of kappa- and delta-opiates in the NTS are mediated via different mechanisms, and provide evidence for selective functional actions of endogenous opioids within brain nuclei.