Alterations in alpha-adrenoceptors in aging intraocular hippocampal grafts.

Abstract Age-related changes of hippocampal α 1 - and α 2 -adrenoceptors were investigated using intraocular hippocampal transplants combined with 3 H-prazocin and 3 H-para-aminoclonidine ( 3 H-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 3 H-PAC binding was significantly reduced in aged grafts as compared to young grafts whereas the 3 H-prazocin binding did not change with age. After sympathetic denervation, both 3 H-PAC and 3 H-prazocin binding increased significantly in young grafts. In aged adrenergically denervated grafts, α 2 -receptor binding was again significantly reduced whereas α 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 α 2 -receptors which is intrinsically determined.