[Calretinin immunoreactivity in olfactory bulb and mucosa in mice]

The vertebrate olfactory system is capable of recognizing and discriminating thousands of different odorant molecules. In vitro biochemical studies have shown that some odorants elicit an increase in the intercellular second messenger cyclic AMP, whereas other odorants cause an increase in the second messenger inositol triphosphate (IP3). If IP3 plays an important role in the signal transduction, calcium-binding protein will be needed. We investigated the expression of calretinin, which belongs to the E-F hand family, in the neonatal and adult olfactory mucosa and olfactory bulb. Mice were sacrificed on postnatal day 1 (P1), day 3 (P3), day 10 (P10) and 12 weeks as adults. The olfactory mucosa of the nasal septum and the olfactory bulb were stained with anti-calretinin antibody at a 1:1000 dilution for 48 hours. The results were as follows. 1) Olfactory mucosa: In the P1 mouse, the olfactory nerves running in the submucosal layer and olfactory cells in the epithelium were positive. In the epithelium, immunopositive spots were seen exclusively in the upper half of the epithelium. In the P3, P10 and adult mice, these spots were seen throughout the olfactory cell layer. However, the basal cell layer and supporting cells were negative. 2) Olfactory bulb: In all stages, the olfactory nerve layer and the glomerular layer were strongly stained. In the external plexiform layer, many cells were positive. Their shape was bipolar and the size of the cell body was thought to be about 20 microns. They were thought to be tufted cells. However, there is a possibility that these cells are short axon cells in the external plexiform layer. In the granule layer, some granule cells were positive. In the P1 mouse, the immunopositive spots were exclusively seen in the upper half of the epithelium. In contrast, in the P3 mouse, these spots were seen throughout the olfactory cell layer. Judging from our results, it is suspected that the important change in neurogenesis of olfactory cells occurred between P1 and P3. In the olfactory bulb, from P1 to adult mice, calretinin was positive in the olfactory nerve layer, the glomerulus and periglomerular cells. In contrast, mitral cells were negative. Most reports state that calcium binding protein appears in periglomerular cells. However, in the external plexiform layer, many cells were positive. As their shape was bipolar and the cell body was a little larger than the periglomerular cells, these cells were thought to be tufted cells.