The tissue localization of the G-protein gamma-subunit, G gamma 8, that is specifically expressed in the olfactory and vomeronasal neurons, was studied in rats at different ages: embryonic day 16, postnatal days 1, 7, 14 and 35, and adult. G8 appears to be a specific marker of the immature olfactory and vomeronasal neurons. Its distribution differs from that of Golf alpha, a G-protein alpha-subunit which is predominantly expressed in mature olfactory neurons. G8 immunoreactivity indicates that an undifferentiated organization of the olfactory epithelium persists up to 3 weeks of age, though neonates possess a functional sense of smell. G gamma 8 accumulates at the highest levels in the axons of the developing olfactory neurons 2 weeks after birth (postnatal day 14). Moreover, up to postnatal day 14, G gamma 8-positive neurons are present in the region of the olfactory and vomeronasal epithelium, where they are not observed in later life. In the olfactory epithelium and in the bulb, G gamma 8 expression becomes weaker and patchy with increasing age, suggesting that the process of continuous regeneration of olfactory neurons occurs in discrete areas. G8-enhanced expression following axotomy indicates that this system is potentially active throughout life. Conversely, in the vomeronasal epithelium G gamma 8 expression persists virtually unmodified in the adult. This indicates that the degree of differentiation may differ between olfactory and vomeronasal neurons.
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