Increased density of perivascular nerves to the major cerebral vessels of the spontaneously hypertensive rat: differential changes in noradrenaline and neuropeptide Y during development

Abstract

Fluorescence and immunohistochemical techniques were used to study the pattern and density of perivascualr nerves containing noradrenaline (NA) and neuropeptide Y (NPY) supplying the major cerebellar of 4-, 6-, 8- and 12-wee-κ-old spontaneously hypertensie rats (SHR) and normotenive Wistar (WIS) controls. Levels of NA and NPY in the superior cervical ganglia were measured. The density of nerves containing NA and NPY was greater in the hypertensive animals at all ages studied. However, the developmental changes in the density of innervation showed similar trends in both SHR and WIS groups. With few exceptions, there was a significant increase in the density of nerves containing NA from 4 to 6 weeks and from 8 to 12 weeks of age. This was in contrast to a low expression, and in some vessels a significant decrease in the number of NPY-containing nerves from 4 to 6 weeks. The density of nerve fibres containing NPY increased significantly in almost all vessels between 6 and 8 weeks of age and then stabilized. Thus there is a differential time course for the appearance of NA and NPY during development. Furthermore, the hyperinnervation of cerebral vessels in SHR by nerves containing NA and NPY precedes the onnset of hypertension and associated medial hypertrophy. High-performance liquidchromatography and enzyme-linked immunosorbant assays show that the NA and NPY content of the superior cervical ganglion do not reflect the changes in innervation pattern seen in the fibres in the cerebral arteries. This tends to support the view that a local neuovascular mechanism in involved in the maintenance of hypertension. The possibility that increase in NPY as well as NA in cerebral periivascular nerves of hypertensive animals is involved in the protection of the blood-brain against oedema and cerebral haemorrhage is raised.