LOCALIZATION OF NEURONAL NITRIC-OXIDE SYNTHASE-IMMUNOREACTIVITY WITHIN SUBPOPULATIONS OF NORADRENERGIC A(1) AND A(2) NEURONS IN THE RATS

The noradrenergic cells of the ventrolateral medulla (VLM) and the nuc leus tractus solitarii (NTS) are implicated in the control of a variet y of cardiovascular, respiratory and neuroendocrine functions. The pre sent study has used antibodies raised against rat neuronal nitric oxid e synthase (nNOS) and tyrosine hydroxylase (TH) to determine whether n NOS is expressed by A(1) and A(2) noradrenergic neurons. Double-labell ing immunofluorescence experiments revealed that approximately 10% of TH-immunoreactive cells in the rostral NTS and 6% in the caudal NTS, w ere immunoreactive for nNOS. In the rostral VLM, only 1% of cells were double-labelled while approximately 9% of the TH-immunoreactive cells in the caudal VLM were immunoreactive for nNOS. These findings indica te that sub-populations of the A(1) and A(2) noradrenergic neurons are capable of generating nitric oxide and suggest a direct role for this neuronal messenger in the regulation of noradrenergic activity within the brain.