The development of beta-adrenergic receptors in the visual cortex of the rat

The development of beta-adrenergic receptors in the rat visual cortex was examined and the density of beta-receptors and associated subtypes (beta 1 and beta 2) was compared between visual and non-visual or whole cortical tissues using radioreceptor assays employing [125I]iodohydroxybenzylpindolol and [125I]iodocyanopindolol as ligands. Saturation assays revealed not only similar affinities of beta-receptors for [125I]iodohydroxybenzylpindolol in visual cortical samples at 10, 24 and 160 days after birth but also practically identical saturation curves for visual and non-visual cortical samples at 160 days of age. Displacement of [125I]iodohydroxybenzylpindolol with propranolol in visual cortical membranes at various postnatal ages showed a gradual increase in receptor density from day 4 to day 24 with no change thereafter. No significant differences were observed in the overall density of beta-receptors or in the distribution and density of beta 1 and beta 2-receptors between visual and non-visual or whole cortical samples; however, there was a definite decline in the density of beta-receptors in these samples between 40 and 160 days of age. The results indicate that the developmental pattern of beta-receptor density and the distribution of beta 1 and beta 2-receptors are similar between visual and whole cortical tissues. In addition, the results emphasize the importance of maintaining the dissociation constant at a fixed value when comparing receptor densities between experiments, and also show the utility of employing the high-affinity ligand, [125I]iodocyanopindolol, with a combination of serotoninergic, dopaminergic and alpha-adrenergic antagonists to examine beta-adrenergic receptors in a specific region of the brain. Study of beta-receptors in the visual cortex may be beneficial in elucidating the role of norepinephrine in this region.