Peptidergic innervation of human cerebral blood vessels and saccular aneurysms

Peptidergic innervation of the human cerebral vasculature has not yet been described in detail and its role in the maintenance of cerebral autoregulat ion still needs to be established. Similarly, few data exist on the innerva tion of vascular malformations. The aim of this study was to clarify the pe ptidergic innervation patterns of human cerebral arteries of various sizes, and, for the first time, that of saccular aneurysms. Light microscopic stu dy of whole-mount preparations of human cerebral arteries and aneurysm sacs resected either during tumor removal or after neck-clipping were carried o ut by means of silver-intensified light microscopic immunocytochemistry vis ualizing neuropeptide-Y, calcitonin gene-related peptide and substance P im munoreactivity. Systematic morphological investigations confirmed the prese nce of longitudinal fiber bundles on the adventitia and a network-like deep er peptidergic system at the adventitia-media border, while in smaller pial and intraparenchymal vessles, only sparse longitudinal immunopositive axon s could be detected. The innervation pattern was totally absent in the wall of saccular aneurysms with the complete disappearance of peptidergic nerve fibers in some areas. To the best of our knowledge neither the disappearan ce of this network on small pial and intraparenchymal vessels, nor the abse nce of an innervation pattern in saccular aneurysms have been described bef ore. Nonhomogeneous peptidergic innervation of the human cerebral vascular tree might be one of the factors responsible for the distinct autoregulator y properties of the capacitance and resistance vessels. Malfunction of this vasoregulatory system might lead to the impairment of autoregulation durin g pathological conditions such as subarachnoid hemorrhage.