Distribution and development of beta-adrenergic receptors in the rat olfactory bulb

Beta-adrenergic stimulation appears to be involved in the establishment of both learned olfactory preferences and functional changes in the olfactory bulb of young rats. We examined the postnatal development of beta-adrenergic receptors within the main olfactory bulb to determine the density and distribution of these receptors. To quantify beta-adrenergic receptor density, olfactory bulb homogenates from postnatal day (PND) 1, 6, 12, and 19 rats were assessed for receptor binding with 125I-iodopindolol. In addition, receptor autoradiography was performed with the selective beta 1 antagonist ICI 89,406 and selective beta 2 antagonist ICI 118,551 on tissue sections from PND 1-30 rats to examine the distribution of the beta-adrenergic receptor subtypes. We observed both an increase in receptor density with increasing age and the formation of distinct spatial distributions of the two beta receptor subtypes within the bulbar lamina. Beta-adrenergic receptors were located in both deep and superficial layers of the bulb. Specifically, beta 1 receptors were present in the granule cell, internal plexiform and glomerular layers. beta 2 receptors were present in the granule cell, internal plexiform, external plexiform, and glomerular layers. High levels of beta 2 receptors also were visible in the meningeal layers between the two bulbs. High densities of beta 1 and beta 2 adrenergic receptors were present within different sets of individual glomeruli by PND 12-19, and the number of these foci increased with age. The knowledge of beta-noradrenergic receptor localization in the bulb may provide the basis for understanding the action of norepinephrine on neural processes in the developing olfactory bulb.