Alterations in opiate receptor binding in the hippocampus of aged Long-Evans rats.
Quantitative in vitro autoradiography was used to examine [3H]D-Ala2, MePhe4, Gly-015 enkephalin (DAGO) (mu-agonist) and [3H]diprenorphine (general opiate antagonist) binding sites in the hippocampal formation of young (6-8 months) and aged (25-28 months) Long-Evans rats. Age-related changes in these binding sites were restricted to specific regions but were not generally dependent on the ligand used. No reliable age-related changes in opiate binding were observed in the CA1 field or subicular region. In contrast, a decrease in the density of binding was found in both dorsal and ventral hippocampus within the CA3 field of aged brains. An age-related decrease in opiate binding within the dentate gyrus differed in its topography at dorsal and ventral levels of the hippocampus. A uniform decrease of opiate receptor binding was found throughout the dorsal dentate gyrus, while a more localized decrease of these sites occurred in hilar and granular layers of the ventral dentate gyrus. These results indicate that a decrease of opiate binding in the hippocampal formation is largely localized to the CA3 region and dentate gyrus of aged rats. These findings are discussed with reference to age-related changes in hippocampal pathways containing opioid peptides. The implications for hippocampal opioid function in learning and age-related cognitive decline are also considered.
Nagahara
A H
AH
Department of Psychology, University of North Carolina at Chapel Hill 27599-3270, USA. anagaha@lucpug.it.luc.edu
Gill
T M
TM
Nicolle
M
M
Gallagher
M
M
D000367:Age Factors; D000375:Aging / Q000187:drug effects*; D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive; D004174:Diprenorphine / Q000494:pharmacology*; D004745:Enkephalins / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051381:Rats; D011957:Receptors, Opioid / Q000187:drug effects* / Q000378:metabolism
D004745:Enkephalins; D011957:Receptors, Opioid; D004174:Diprenorphine