Chemical stimulation of the nucleus locus coeruleus: cardiovascular responses and baroreflex modification.

Microinjection of glutamate (Glu, 2.5 nmol) or homocysteic acid (HA, 0.1-0.5 nmol) into the nucleus locus coeruleus (LC) decreased both blood pressure and heart rate. These microinjections also produced a facilitatory or occlusive effect on depressor and bradycardiac responses evoked by electrical stimulation of the aortic depressor nerve (ADN). Destruction of the nucleus tractus solitarius (NTS), which totally eliminated ADN-evoked responses, had no effect on the cardiovascular responses evoked by LC stimulation. These results suggest that the neuronal populations that contribute to the LC-induced cardiovascular responses overlap at least partly with the baroreflex substrate other than the NTS.