Differential gene expression profiles of the olfactory bulb after nasal obstruction in neonatal rats

A subtype-specific critical period for neurogenesis in the postnatal development of mouse olfactory glomeruli

Sensory input is essential for the normal development of sensory centers in the brain, such as the somatosensory, visual, auditory, and olfactory systems. Visual deprivation during a specific developmental stage, called the critical period, results in severe and irreversible functional impairments in the primary visual cortex. Olfactory deprivation in the early postnatal period also causes significant developmental defects in the olfactory bulb, the primary center for olfaction. Olfactory bulb interneurons are continuously generated from neural stem cells in the ventricular-subventricular zone, suggesting that the olfactory system has plasticity even in adulthood. Here, we investigated the effect of transient neonatal olfactory deprivation on the addition of interneurons to the glomerular layer of the adult mouse olfactory bulb. We found that the addition of one subtype of interneurons was persistently inhibited even after reopening the naris. BrdU pulse-chase experiments revealed that the neonatal olfactory deprivation predominantly affected an early phase in the maturation of this neuronal subtype in the olfactory bulb. Subjecting the mice to odor stimulation for 6 weeks after naris reopening resulted in significant recovery from the histological and functional defects caused by the olfactory deprivation. These results suggest that a subtype-specific critical period exists for olfactory bulb neurogenesis, but that this period is less strict and more plastic compared with the critical periods for other systems. This study provides new insights into the mechanisms of postnatal neurogenesis and a biological basis for the therapeutic effect of olfactory training.

The effects of unilateral naris occlusion on gene expression profiles in mouse olfactory mucosa

Unilateral naris occlusion has been the method of choice for effecting stimulus deprivation in studies of olfactory plasticity. Early experiments emphasized the deleterious effects of this technique on the developing olfactory system while more recent studies have pointed to several apparently "compensatory" responses. However, the evidence for deprivation-induced compensatory processes in olfaction remains fragmentary. High-throughput methods such as microarray analysis can help fill the deficits in our understanding of naris occlusion as a mode of stimulus deprivation. Here we report for young adult mice the effects of early postnatal naris occlusion on the olfactory mucosal transcriptome using microarray analysis with RT-PCR confirmation. The transcripts of key genes involved in olfactory reception, transduction, and transmission were up-regulated in deprived-side olfactory mucosa, with opposite effects in non-deprived-side mucosa, compared to controls. Results support the hypothesis that odor environment triggers a previously unknown homeostatic control mechanism in olfactory receptor neurons designed to maximize information transfer.