A morphometric study of the effect of bilateral cervical sympathetic ganglionectomy on the architecture of pial arteries in spontaneously hypertensive and normotensive rats.

The influence of the cranial sympathetic nerves on the architecture of pial arteries in normo- and hypertension was examined. For this purpose the effect of bilateral superior cervical ganglionectomy was evaluated in normotensive rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). The operations were performed at the age of 1 wk, which is just prior to the onset of ganglionic transmission. The length of the inner media contour was measured and the media cross-sectional area was determined planimetrically, with computerized digitalization of projected photographic images of transversely sectioned pial arteries. Four wk after sympathectomy there was a 20% reduction in media cross-sectional area and a consequent reduction in the ratio between media area and calculated luminal radius in the major pial arteries at the base of the brain in WKY but not in SHRSP. Conversely, in small pial arteries linear regression analysis showed that in WKY subjected to ganglionectomy the relationship between media cross-sectional area and luminal radius was significantly larger in arteries with a radius less than 21 microns compared to untreated WKY. No such effect was seen in the corresponding SHRSP vessels. In addition, the cross-sectional area of the internal elastic membrane (IEM) in the basilar arteries of WKY was measured by means of a computerized image-analysing system. Mean cross-sectional area of the IEM was approximately 45% larger following SE than in control animals. The present findings propose a 'trophic' role for the sympathetic perivascular nerves in large pial arteries of the rat. The increased media-radius ratio in the small pial arteries of the WKY following sympathectomy might reflect a compensatory hypertrophy due to reduced protection from the larger arteries against the pressure load. The inability to detect any morphometrically measurable effect of the sympathectomy in the cerebral arteries of SHRSP is probably explained by a marked growth-stimulating effect of the high pressure load in these animals.