Effect of rat subarachnoid hemorrhage on serotonin innervation of the cerebral ventricular wall and serotonin neurons of the ventral surface of the brain stem: an immunohistochemical study.

The effect of subarachnoid hemorrhage on serotonin (5-HT) innervation of the cerebral ventricles and on 5-HT neurons in the ventral surface of the brain stem was studied immunohistochemically in the rat. Subarachnoid hemorrhage (SAH) was induced by injection of autologous arterial blood into the cisterna magna. In normal and sham-operated animals, the entire ependyma of the ventricles was supplied with 5-HT-immunoreactive supraependymal nerves. The ependyma in the dorsal third ventricle received the most dense innervation. 5-HT neurons on the surface of the brain stem were found in the median fissure and on the ventral surface of the pyramidal tract. A marked reduction in supraependymal 5-HT immunostaining was observed in animals sacrificed as early as 6 h post-SAH and this change continued until 14 days and recovered by 28 days following SAH. 5-HT neurons on the ventral surface of the brain stem were visible even in the rat with SAH. The results suggest that SAH caused a transient depletion of 5-HT immunoreactivity in the supraependymal nerves but 5-HT neurons on the ventral surface of the brain stem were unchanged. Depletion of 5-HT immunoreactive nerves on the cerebral ventricular wall might be involved in the pathophysiology after SAH.