LOCAL NADPH DIAPHORASE NEURONS INNERVATE PIAL-ARTERIES AND LIE CLOSE OR PROJECT TO INTRACEREBRAL BLOOD-VESSELS - A POSSIBLE ROLE FOR NITRIC-OXIDE IN THE REGULATION OF CEREBRAL BLOOD-FLOW

Electrical stimulation of perivascular nerves induced a relaxation of endothelium-denuded cat pial arteries that was significantly reduced b y nitric oxide (NO) synthase inhibition, indicating that NO was involv ed in the neurogenic relaxation of these vessels. Histochemical staini ng of the pial arteries for NADPH-diaphorase (NADPH-d), used as a mark er for NO synthase, showed positive nerve fibers in the adventitial la yer. Interestingly, in some restricted areas stained neuronal cell bod ies were also observed. These neurons were scattered or distributed in small groups in a ganglion-like manner, and they sent fibers to the v essel wall. No NADPH-d-positive nerve fibers or cell bodies were detec ted in forelimb, pulmonary, or coronary arteries. Within the brain par enchyma, blood vessels also showed positive fibers around their walls. These fibers were organized in a branching pattern and presented vari cosities. NADPH-d-positive neurons were found in the proximity of the intracerebral vascular profiles, sending processes to the vessels and/ or being directly apposed to their wall. The neurovascular contacts we re preferentially located close to the interface between the cerebral cortex and white matter. The anatomical relationship between NADPH-d-p ositive neurons and fibers and the cerebral blood vessels, together wi th the participation of NO in the neurogenic relaxation of pial arteri es, suggests that NO is involved in the regulation of cerebral blood f low.