A LEARNED ODOR EVOKES AN ENHANCED FOS-LIKE GLOMERULAR RESPONSE IN THEOLFACTORY-BULB OF YOUNG-RATS

Young rats exposed to peppermint odor and reinforcing tactile stimulat ion from postnatal days (PND) 1-18 increase their preference for that odor relative to controls. This early olfactory memory is accompanied by an 80% increase in the density of glomerular-layer cells displaying Fos-like immunoreactivity in response to the learned odor on PND 19. The difference is observed in midlateral portions of the olfactory bul b that align with foci of 2-deoxyglucose (2-DG) uptake in adjacent sec tions. Trained and control animals are not different in the Fos-like r esponse of juxtaglomerular cells within ventrolateral 2-DG foci. Ratio s of midlateral/ventrolateral response differ significantly between tr ained and control animals and include differences among cells of three staining intensities. These ratios are correlated with ratios of 2-DG uptake (midlateral/venrrolateral foci), which also differ significant ly between trained and control rats. Juxtaglomerular cells associated with 2-DG foci also express Egr-1-like immunoreactivity. However, the midlateral Egr-1 response does not differ between trained and control rats. These results show that early memories can be associated with an increased Fos-like response in a primary sensory area of the CNS. The y also suggest that only specific regions within the olfactory bulb ar e modified following the learning of a given odor in early life.