Changes in the serotonergic system in the main olfactory bulb of rats unilaterally deprived from birth to adulthood

Abstract

[EN]The serotonergic system plays a key role in the modulation ofolfactory processing. The present study examined the plasticresponse of this centrifugal system after unilateral narisocclusion, analysing both serotonergic afferents and receptorsin the main olfactory bulb. After 60 days of sensory depriva-tion, the serotonergic system exhibited adaptive changes.Olfactory deprivation caused a general increase in the numberof fibres immunopositive for serotonin but not of thoseimmunopositive for the serotonin transporter. HPLC datarevealed an increase in serotonin levels but not in those of itsmajor metabolite, 5-hydroxyindole acetic acid, resulting in adecrease in the 5-hydroxyindole acetic acid/serotonin ratio.These changes were observed not only in the deprived butalso in the contralateral olfactory bulb. Double serotonin–tyrosine hydroxylase immunolabelling revealed that theglomerular regions of the deprived olfactory bulb with a highserotonergic fibre density showed a strong reduction in tyro-sine hydroxylase. Finally, the serotonin 2A receptor distributiondensity and the number of juxtaglomerular cells immuno-positive for serotonin 2A receptor remained unaltered afterolfactory deprivation. Environmental stimulation modulatedthe serotonergic afferents to the olfactory bulb. Our resultsindicate the presence of a bilateral accumulation of serotoninin the serotonergic axon network, with no changes in sero-tonin 2A receptor density after unilateral olfactory deprivation