FOS PROTEIN IMMUNOREACTIVITY IN THE DEVELOPING OLFACTORY BULBS OF NORMAL AND NARIS-OCCLUDED RATS

Immediate early genes such as c-fos may be a route through which extra cellular events affect genomic expression. Expression of immediate ear ly genes is important in the transcriptional regulation necessary for the normal development of the nervous system. Developmental patterns o f Fos protein (the product of c-fos immediate early gene expression) w ere studied in the main olfactory bulb of the rat using immunocytochem istry. Embryonic Day 21 (E21, the last prenatal day), as well as Postn atal Day 0 (P0), P1, P5, P10, P15, P20 and P30 subjects were examined. Although staining was absent in the E21 bulb, there was a rapid onset of Fos synthesis within hours after birth. Distribution of Fos-immuno reactive (Fos-ir) nuclei corresponded to the sequence of bulb maturati on: numerous mitral/tufted and granule cells were labeled on PO, follo wed by the appearance of Fos-ir in the nuclei of periglomerular cells and an increase in the number of stained granule cells with developmen t. Surgical closure of an external naris on P1 resulted in a 70% reduc tion in the number of Fos-ir granule cell nuclei as early as 2 h after the manipulation. During the next 30 days, levels of Fos staining fur ther diminished in experimental bulbs when compared to their contralat eral controls. Nevertheless, electrical stimulation of the contralater al bulb in P20 pups resulted in a robust increase of Fos labeling in m ost main and accessory olfactory bulb mitral cells and in many granule and periglomerular neurons, suggesting that the experimental bulbs re main competent to express Fos protein.