Neuropeptide Y: cerebrovascular innervation and vasomotor effects in the cat

Avian pancreatic polypeptide (APP) has been proposed to be a neurotransmitter in a subpopulation of sympathetic nerves. Here, we present immunocytochemical and pharmacological evidence that the structurally related peptide, neuropeptide Y (NPY), is likely to be the biologically active material in these nerves. Cerebral arteries from cats are invested with a dense network of NPY-containing nerve fibres, as demonstrated by immunocytochemistry. This immunoreaction is abolished by prior removal of the superior cervical ganglion. NPY causes strong contractions of cerebral arteries in vitro whereas APP has small effects on the vasomotor reactivity. The NPY-induced contractions were not inhibited by the alpha 2-adrenoceptor antagonist rauwolscine (10(-7) M) or the 5-hydroxytryptamine antagonist ketanserin (10(-7) M). The contractions were, however, sensitive to calcium removal or to the calcium antagonist diltiazem (10(-4) M).