Cerebral perivascular nerves in subarachnoid hemorrhage. A histochemical and immunohistochemical study

The authors have studied the changes induced by subarachnoid hemorrhage (SAH) in the density and distribution of cerebral perivascular nerves in monkeys and rats. The SAH was induced in monkeys by placement of an autologous blood clot after opening the basal cisterns over the arteries of the circle of Willis on one side. In the rat study, SAH was induced by injection of autologous arterial blood into the cisterna magna. The nerves examined were adrenergic nerves, acetylcholinesterase (AChE)-containing nerves, vasoactive intestinal polypeptide (VIP)-like immunoreactive nerves, and substance P-like immunoreactive nerves. In the monkey study, all animals underwent baseline cerebral angiography, then had repeat angiography just before sacrifice on Day 2, 7, 28, or 70 after SAH. Two sham-operated monkeys underwent the surgical procedure without clot placement and were sacrificed on postoperative Day 7, after repeat angiography. Clot placement in monkeys reduced staining of all middle cerebral artery (MCA) perivascular nerves for between 2 and 28 days post-SAH. The number of stained nerve fibers of MCA's on the non-operated side was slightly reduced on Days 2 and 7 after SAH. Sham-operated monkeys showed a mild reduction of staining in all nerves, but only on the operated side. Cerebral vasospasm was observed on all angiograms taken on Days 2 and 7 following SAH. No vasospasm was found in normal or sham-operated monkeys. The disappearance of nerve staining without associated vasospasm was found on the operated side of the sham-operated monkeys and on the clot side of the animal sacrificed on Day 28 after SAH. Rats sacrificed on Days 2 and 7 post-SAH showed reduction in adrenergic and VIP-like immunoreactive staining around basilar arteries, while nerves containing AChE were not affected. Saline-injected rats exhibited no change in the appearance of perivascular innervation. These results suggest that SAH as well as surgical manipulation of the vessel wall caused a reduction of the studied substances in cerebral perivascular nerves. This reduction in immunoreactive staining of perivascular nerves did not correlate with the development of angiographic vasospasm after SAH.