Age-dependent day/night variations of alpha 1- and beta-adrenoceptors in the rat cerebral cortex.

Receptor binding studies in the cerebral cortex of young (2-4 months) and mature (11-12 months) rats were conducted at two points of the circadian time: 8.00 and 20.00 hr. In addition, the exploratory activity in the open field was assessed. In young rats the density of alpha 1- and beta-adrenoceptors increased at 20.00 in comparison with 8.00 hr, while no changes in the exploratory activity were observed. However, in mature rats the activity was higher at 20.00 than 8.00 hr; at the same time, a rise in the density of alpha 1- but not beta-adrenoceptors was observed. Obtained data suggest that the increased exploratory activity of mature rats at 20.00 hr may appear as a result of a higher density of alpha 1-adrenoceptors and a simultaneous lack of changes in beta-adrenoceptors.