Effect of Selective Lesions in the Hypothalamic—Pituitary Region on the Development of Cerebral Vasospasm following an Experimental Subarachnoid Hemorrhage in the Rat

Intracisternal injection of blood in the rat induced an angiographically demonstrable biphasic cerebral vasospasm with a maximal acute spasm at 10 min and a maximal late spasm at 2 days after the subarachnoid hemorrhage. Systemic administration of 6-hydroxydopamine, which destroys catecholamine fibers in the circumventricular areas characterized by the absence of a blood–brain barrier, prevented the development of both the acute and the late spasm. Isolation or removal of one of the circumventricular organs, the pituitary, from the brain via a stalk transection or a hypophysectomy did not affect the degree of vasospasm. Lesion of the median eminence, another region without a blood–brain barrier, prevented the development of both types of spasm. The median eminence receives projections from the A₁ and A₂ nuclei in the medulla oblongata. It is suggested that the projections of these nuclei to the internal layer of the median eminence underlie the development of spasm.