Co-existence of immunoreactivity to neuropeptide Y and vasoactive intestinal peptide in non-noradrenergic axons innervating guinea pig cerebral arteries after sympathectomy.

We have used double-labelling immunofluorescence to examine the coexistence of immunoreactivity (IR) to neuropeptide Y (NPY), tyrosine hydroxylase (TH) and vasoactive intestinal peptide (VIP) in autonomic neurons innervating guinea pig cerebral arteries. In the rostral circle of Willis of control animals. NPY-IR was detected in 86% of axons with TH-IR (noradrenergic) and 18% of VIP-IR (non-noradrenergic) axons. No axons contained both VIP-IR and TH-IR. Ten to 12 days after bilateral removal of the superior cervical ganglia all TH-IR axons had disappeared. The density of VIP-IR axons was unchanged but now 70% of VIP-IR axons contained NPY-IR. These results show that NPY is not exclusively associated with noradrenergic axons in the cerebral vasculature. Furthermore, NPY levels in non-noradrenergic axons increased following sympathetic denervation.