Alterations in dihydromorphine binding in cerebral hemispheres of aged male rats

Equilibrium binding of [3H]dihydromorphine was assayed in brain regions of young and aged male F344 rats. Young rats had significantly higher receptor densities than old rats in the frontal poles, anterior cortex, and striatum. In the frontal poles, the decline in receptor concentration with age was accompanied by a significant increase in the apparent affinity of dihydromorphine for receptors, which may be compensatory for the decrease in Bmax. This pattern of receptor alterations is different than that previously observed in aged female rats. Therefore, processes which underlie synaptic alterations with age may be different in males and females.