Involvement of the A1 cell group in baroreceptor inhibition of neurosecretory vasopressin cells.

Extracellular recording experiments were done to investigate the proposal that arterial baroreceptor inhibition of vasopressinergic (AVP) neurosecretory cells involves the A1 noradrenaline cell group of the caudal medulla. The responsiveness of functionally identified AVP cells of the rat supraoptic nucleus to baroreceptor activation was not discernibly altered by A1 region lesions even though AVP cell responses to certain other stimuli were abolished. Acute blockade of A1 region function by injection of gamma-aminobutyric acid sometimes impaired AVP cell responsiveness to baroreceptor stimulation, although more commonly there was no effect. These data suggest that the A1 cell group is not an essential component in pathways mediating baroreceptor inhibition of neurosecretory AVP cells, but may contribute to the sensitivity of AVP cells to this input.