EARLY LOCUS-COERULEUS LESIONS INCREASE THE DENSITY OF BETA-ADRENERGICRECEPTORS 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.(16) Beta-adrenergic receptors are located in nearly all bulb laminae, wit h high-density foci of beta-1 and beta-2-adrenoceptors present in the glomerular layer.(29) Early olfactory experiences that increase norepi nephrine levels in the bulb also decrease the density of beta-1- and b eta-2-adrenoceptors, as well as the number of high-density glomerular foci of beta-2-receptors.(30) Changes in bulb norepinephrine levels, t herefore, may affect the density of beta-adrenoceptors in the bulb. In the current study, we test this hypothesis by performing unilateral l esions of the locus coeruleus with 6-hydroxydopamine on postnatal day 4, and examining the density of beta-1- and beta-2-adrenergic receptor s in the main olfactory bulb of the rat using I-125-labeled iodopindol ol receptor autoradiography on postnatal day 19. Locus coeruleus destr uction resulted in a statistically significant increase in the density of adrenergic receptors in the ipsilateral bulb compared to the contr alateral 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 b eta-adrenergic receptors in the bulb. Copyright (C) 1996 ISDN.