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

Abstract

The serotonergic system plays a key role in the modulation of olfactory processing. The present study examined the plastic response of this centrifugal system after unilateral naris occlusion, analysing both serotonergic afferents and receptors in the main olfactory bulb. After 60 days of sensory deprivation, the serotonergic system exhibited adaptive changes. Olfactory deprivation caused a general increase in the number of fibres immunopositive for serotonin but not of those immunopositive for the serotonin transporter. HPLC data revealed an increase in serotonin levels but not in those of its major metabolite, 5-hydroxyindole acetic acid, resulting in a decrease in the 5-hydroxyindole acetic acid/serotonin ratio. These changes were observed not only in the deprived but also in the contralateral olfactory bulb. Double serotonintyrosine hydroxylase immunolabelling revealed that the glomerular regions of the deprived olfactory bulb with a high serotonergic fibre density showed a strong reduction in tyrosine hydroxylase. Finally, the serotonin 2A receptor distribution density and the number of juxtaglomerular cells immunopositive for serotonin 2A receptor remained unaltered after olfactory deprivation. Environmental stimulation modulated the serotonergic afferents to the olfactory bulb. Our results indicate the presence of a bilateral accumulation of serotonin in the serotonergic axon network, with no changes in serotonin 2A receptor density after unilateral olfactory deprivation. Keywords: 5-hydroxyindole acetic acid, olfactory system, serotonin, serotonin receptor, serotonin transporter, unilateral deprivation. J. Neurochem. (2007) 100, 924-938. Afferent activity is needed for the development and maintenance of the normal structural and biochemical features of the olfactory system (Brunjes 1994). Dramatic alterations occur in the main olfactory bulbs (MOBs) ipsilateral to deprivation of rats and mice after occlusion of an external naris. Marked anatomical changes, including volume reduction, occur after deprivation from birth up to postnatal day (P)20. However, naris closure performed after P20 results in few anatomical changes (Brunjes 1994). One day of deprivation (from P1 to P2) causes the attenuation of electrophysiological and metabolic neural activities in the rat MOB (Korol and Brunjes 1990). Forty-five days of odour deprivation affects the maturation of newborn granule cells, causing a decrease in the complexity of their dendritic arborization and spine density (Saghatelyan et al. 2005). Some changes are dependent on a temporal window. Thus, volume reduction is not observed in the MOB after naris closure on P40, although down-regulation of activity has been clearly demonstrated using 2-deoxyglucose uptake analysis (Korol and Brunjes 1990). Finally, some changes

Transcriptome Profile and Cytogenetic Analysis of Immortalized Neuronally Restricted Progenitor Cells Derived from the Porcine Olfactory Bulb

“…Within a similar context, the expression of necdin, a member of the melanoma antigen protein family, recently has been shown to augment the differentiation and specification of GABAergic neurons (15). In addition to the GABA-and glutamatergic character of the OBGF400 cells, the serotonergic system modulates the olfactory processing system (30). Serotonin selectively influences signal transduction via classical synaptic stimulation or non-junctional transmission and serotonin neurons often coexist with neuropeptides (31); OBGF400 neuroblasts expressed the serotonin receptors 2A and 2C concurrently with the neuropeptide Y, a modulator of excitatory synaptic transmission in the OB (32).…”

Activity-Dependent Changes in Cholinergic Innervation of the Mouse Olfactory Bulb

“…Counter to what one might have predicted, it has been reported that olfactory input does not influence cholinergic innervation [14], though it significantly affects the noradrenergic [14], [15] and serotonergic [16] systems. Such a counterintuitive result may have been due to the choice of acetylcholine esterase (AChE) staining [14], which is less specific [17] as a marker for cholinergic fibers, and from the lack of stringent quantitation.…”

Experience-Dependent Modification of Primary Sensory Synapses in the Mammalian Olfactory Bulb

“…Here, we pharmacologically isolated the intrinsic properties of primary sensory synapses (baseline release of transmitter and activation ionotropic glutamate receptors) by using sulpiride to block D 2 receptors and CGP55845 to block GABA B receptors. Future investigations should focus on interactions between sensory experience, plasticity at OSN synapses, and several key neuromodulators known to affect glomerular physiology, particularly mGluRs (De Saint Jan and Westbrook, 2005;Yuan and Knopfel, 2006;De Saint Jan and Westbrook, 2007), dopamine (Guthrie et al, 1991;Wilson and Sullivan, 1995;Cho et al, 1996;Berkowicz and Trombley, 2000;Ennis et al, 2001), norepinephrine (Nadi et al, 1981;Wilson and Leon, 1988b;Brennan et al, 1990;Brinon et al, 2001), and serotonin (Hardy et al, 2005;Gomez et al, 2007). For example, does odor experience induce differential modulation of D 2 receptor isoforms at OSN synapses?…”