Early olfactory enrichment and deprivation both decrease beta-adrenergic receptor density in the main olfactory bulb of the rat.

Abstract

The density of noradrenergic locus coeruleus projections and beta-adrenergic receptors in the main olfactory bulb of the rat increases with age. Both beta 1- and beta 2-adrenergic receptor subtypes exhibit laminar distributions, with focal regions of high receptor density present within the neuropil of individual glomeruli. Since the first synaptic contacts between olfactory receptor neurons and bulbar neurons occur within the glomeruli, early olfactory experiences possibly could influence the density or distribution of beta-adrenergic receptors in the bulb. We therefore investigated the effects of olfactory deprivation and early olfactory enrichment on the density and distribution of beta-adrenergic receptors in the main olfactory bulb. Animals were subjected to either unilateral naris closure on postnatal day 1 or odor training from postnatal days 1-18. Bulbs were removed on postnatal day 19 and subjected to quantitative autoradiography using the beta-adrenergic receptor antagonist [125I]iodopindolol and specific receptor subtype antagonists ICI 118,551 (beta 2-antagonist) and ICI 89,406 (beta 1-antagonist). Unilateral naris occlusion decreased both the number of beta 2 glomerular foci and the density of beta 1 and beta 2 receptors in the deprived bulb compared to the nondeprived bulb. Early odor training resulted in a significant decrease in the number, area, and receptor density of beta 2 glomerular foci in the midlateral region of the bulb. The distribution of beta 2 glomerular foci also differs with these two sensory manipulations. Changes in beta-adrenergic receptor density in response to both early learning and olfactory deprivation may be induced by a transient increase in olfactory bulb norepinephrine.