ABSTRACT
Neurogenesis has long been recognized as a property of the adult olfactory epithelium. Over 50 years ago mitotic activity was first observed in the olfactory epithelium of adult mice (Nagahara, 1940). Olfactory sensory neurons regenerate in monkey (Graziadei et al, 1980; Schultz, 1941) and human (Murrell et al, 1996; Wolozin et al., 1992). Human olfactory neurogenesis continues into old age, making the olfactory system one of the most continually variable regions of the nervous system. It is now recognized that neurogenesis occurs in a nuinber of sites within the adult brain. A recent study has even identified newly formed neurons in the brain of aged humans (Eriksson et al., 1998). Sites of neurogenesis in the brain include the dentate gyrus and the subventricular zone of the forebrain (recently reviewed in Scheffler et al., 1999), Neurogenesis in the subventricular zone gives rise to neurons which migrate forward to populate the olfactory bulb, providing interneurons in the periglomerular and granule cell layers (Luskin, 1993).
