Nerve fiber production by intraocular adrenal medullary grafts: stimulation by nerve growth factor or sympathetic denervation of the host iris.

This study evaluates the production of adrenergic nerve fibers by adrenal medullary tissue of the adult rat grafted to the anterior chamber of the eye of adult recipients. The chromaffin grafts attach to and become vascularized by the host iris. They decrease in size intraocularly during the first 3 weeks. This decrease is somewhat counteracted by sympathetic denervation of the host iris, and better counteracted by sympathetic denervation and addition of nerve growth factor (NGF, given at grafting and 1 and 2 weeks after grafting). Outgrowth of adrenergic nerve fibers from the grafts into the host iris was studied in wholemount preparations by use of the Falck-Hillarp technique 3 weeks after grafting. The innervated area of the host iris was approximately doubled in the chronically sympathectomized group and doubled again in the chronically sympathectomized NGF-supplemented group. Chronic sympathetic denervation had no effect on density of outgrowing nerves, whereas addition of NGF more than doubled nerve density. Since sympathetic denervation causes a slight elevation of NGF activity in the iris, the present experiments are taken as evidence that the level of NGF in the iris regulates formation of nerve fibers by adrenal medullary tissue grafts from adult rats.