Bilateral olfactory deprivation reveals a selective noradrenergic regulatory input to the olfactory bulb

Unilateral olfactory deprivation in the rat induces changes in the catechol aminergic system of the olfactory bulb. Nevertheless, evidence suggests tha t unilateral deprivation does not fully prevent stimulation of the deprived bulb. The present report analyses the response of the catecholaminergic sy stem of the olfactory bulb in fully deprived rats obtained by bilateral nar is occlusion. The complete deprivation produces more rapid and dramatic cha nges in both the intrinsic and extrinsic catecholaminergic systems of the o lfactory bulb. Intrinsic responses involve a rapid decrease in dopamine-con taining cells to about 25% of controls, correlated with a decreased Fos exp ression in juxtaglomerular cells of all olfactory glomeruli, with the only exception of those of the atypical glomeruli which maintain unaltered expre ssion of both markers. In parallel with these events, there is a progressiv e increase in the density of extrinsic noradrenergic axons arising from neu rons in the locus coeruleus, which shows, in parallel, a progressive increa se in Fos expression. This model demonstrates plastic changes in the catech olaminergic system of the olfactory bulb forming a valid morphological subs trate for lowering thresholds in the processing of olfactory information. I n addition to this generalized response, there is another one, directed to a specific subset of olfactory glomeruli (atypical glomeruli) involved in t he processing of odor pheromone-like cues related to behavioral responses, that could be responsible for keeping active this reduced and selected grou p of glomeruli carrying crucial olfactory information. These results indicate the existence of adaptive changes in the catecholami nergic system of the olfactory bulb as a response to the lack of afferent p eripheral stimulation. These changes involve dopamine- and noradrenaline-im munoreactive elements, in a strategy presumably directed at maintaining to the highest possible level the ability to detect olfactory signals. (C) 200 1 IBRO. Published by Elsevier Science Ltd. All rights reserved.