Hippocampal alpha- and beta-adrenergic receptors: comparison of [3H]dihydroalprenolol and [3H]WB 4101 binding with noradrenergic innervation in the rat.

The relationship of alpha- and beta-adrenergic receptors to the noradrenergic innervation of the rat hippocampal formation was studied with histofluorescent, biochemical, and radioligand binding methods. The dentate gyrus received a major portion of the innervation and contained twice the norepinephrine content of the hippocampal gyrus. However, the density of beta-adrenergic receptors, determined by [3H]dihydroalprenolol (DHA) binding, was approximately equal in both gyri. By contrast, a presumed alpha-adrenergic binding site was relatively concentrated in the dentate gyrus, roughly correlating with the distribution of the noradrenergic innervation. Although a significant concentration of beta-adrenergic receptors in the pyramidal cell layer had been suggested in previous studies with fluorescent analogs of propranolol, direct microchemical measurements of [3H]DHA binding in stratum pyramidalis and stratum radiatum showed that beta-adrenergic receptors were uniformly distributed in the hippocampal gyrus. These data, demonstrating a ubiquitous distribution of beta-adrenergic binding in a brain region with a well-defined noradrenergic input, suggest that a portion, perhaps a majority, of beta-adrenergic receptors are not associated with noradrenergic nerve terminals.