Early locus coeruleus lesions increase the density of beta-adrenergic receptors in the main olfactory bulb of rats.

Norepinephrine is supplied to both deep and superficial layers of the olfactory bulb through dense projections from the locus coeruleus. Beta-adrenergic receptors are located in nearly all bulb laminae, with high-density foci of beta-1 and beta-2-adrenoceptors present in the glomerular layer. Early olfactory experiences that increase norepinephrine levels in the bulb also decrease the density of beta-1- and beta-2-adrenoceptors, as well as the number of high-density glomerular foci of beta-2-receptors. Changes in bulb norepinephrine levels, therefore, may affect the density of beta-adrenoceptors in the bulb. In the current study, we test this hypothesis by performing unilateral lesions of the locus coeruleus with 6-hydroxydopamine on postnatal day 4, and examining the density of beta-1- and beta-2-adrenergic receptors in the main olfactory bulb of the rat using 125I-labeled iodopindolol receptor autoradiography on postnatal day 19. Locus coeruleus destruction resulted in a statistically significant increase in the density of adrenergic receptors in the ipsilateral bulb compared to the contralateral bulb. Both beta-1- and beta-2-adrenoceptor subtypes increased in density with this manipulation, although the number of glomerular layer high-density beta-2 foci was not significantly different between the two bulbs. These results are consistent with the hypothesis that changes in olfactory bulb norepinephrine can regulate the density of beta-adrenergic receptors in the bulb.