Diurnal rhythm of alpha 2-noradrenergic receptors in the paraventricular nucleus and other brain areas: relation to circulating corticosterone and feeding behavior.

The paraventricular nucleus alpha 2-noradrenergic system and the glucocorticoid hormone, corticosterone, are known to modulate feeding behavior and exhibit a circadian pattern which may be related to the natural periodicity of feeding in the rat. The results of the present study indicate that the binding of [3H]p-aminoclonidine to alpha 2-noradrenergic receptors specifically in the paraventricular nucleus varies concomitantly with plasma corticosterone levels, as well as spontaneous feeding. A monophasic peak of paraventricular noradrenergic receptor binding is detected at the onset of the dark period, when corticosterone levels are highest and feeding is initiated. On the other hand, the supraoptic nucleus exhibits the reverse diurnal pattern, i.e., a significant decline of [3H]p-aminoclonidine binding at the onset of the dark period. Other hypothalamic and extra-hypothalamic areas fail to show significant changes in alpha 2-noradrenergic receptors as a function of the diurnal cycle. This study supports other evidence indicating a close interaction between circulating corticosterone and alpha 2-noradrenergic receptors in specific hypothalamic areas. It also reveals a potential importance for this interaction in control of the natural feeding rhythm.