Thymus-induced recovery of age-related decrease of brain cortex alpha- and beta-adrenoceptors.

It has previously been demonstrated that thymus exerts a regulatory influence on beta-adrenergic system during aging. In particular, it has been shown that thymus can correct the beta-adrenoceptor density decrease in old mice. In the present paper results of experiments are reported dealing with the influence of the thymus on alpha-adrenoceptors of mouse brain cortex. Both subtypes of alpha-adrenoceptors are studied separately, using different labelled ligands. Results show that alpha 1-adrenoceptor density decreases in old animals, while alpha 2-adrenoceptor density does not change significantly. A neonatal thymus grafted into old recipients is capable of correcting the alteration observed in old mice. The differential impairment of alpha-adrenoceptors resembles that one previously observed on beta-adrenoceptors, where beta 1-type decreases in number during aging with a parallel decrease of adenylyl-cyclase activity, while beta 2-type remains unchanged.