Alterations in alpha-adrenoceptors in aging intraocular hippocampal grafts.

Age-related changes of hippocampal alpha 1- and alpha 2-adrenoceptors were investigated using intraocular hippocampal transplants combined with 3H-prazocin and 3H-para-aminoclonidine (3H-PAC) autoradiography. Young hippocampal grafts in young hosts and old grafts in old hosts innervated by noradrenergic sympathetic fibers were studied. In addition, young and old hippocampal grafts were examined following noradrenergic denervation by superior cervical ganglion removal. The 3H-PAC binding was significantly reduced in aged grafts as compared to young grafts whereas the 3H-prazocin binding did not change with age. After sympathetic denervation, both 3H-PAC and 3H-prazocin binding increased significantly in young grafts. In aged adrenergically denervated grafts, alpha 2-receptor binding was again significantly reduced whereas alpha 1-receptor binding was not significantly different from that in young denervated grafts. Taken together, these results indicate a selective age-related reduction in hippocampal postsynaptic alpha 2-receptors which is intrinsically determined.