SUPPORTING CELL-PROLIFERATION IN THE OLFACTORY EPITHELIUM DECREASES POSTNATALLY

It is well known that progenitor cells in the basal layer of olfactory epithelium proliferate continuously throughout life; the offspring of these dividing cells produce replacements for receptor neurons. In th e rat the number of proliferating basal cells/mm length of epithelium (proliferation density) decreases with postnatal age while the area of the olfactory sheet increases. The supporting cells, which act as the glia of the olfactory epithelium, also divide. We examined in detail some aspects of the dynamics of olfactory supporting cell proliferatio n to determine whether their rate of proliferation changes with age, a nd how it compares with the rate in basal progenitor cells. Using BrdU to label dividing cells, we determined the proliferation density of s upporting cells and basal cells in 10 mu m coronal sections from six d ifferent anterior-posterior regions in rats ranging in age from birth (P1) until P333. We observed a dramatic decrease in supporting cell pr oliferation density from P1 (80 cells/mm) to P11 (32 cells/mm) to P21 (12 cells/mm); the density decreases continuously to P333 (0.4 cells/m m). This reduction was even more dramatic than that in the basal cell population (Weiler and Farbman, 1997). Analysis of the data for correl ation between basal and supporting cell proliferation revealed a weak correlation in neonates but no correlation in older animals. This sugg ests that the mechanisms that regulate proliferation of the two cell t ypes are different. Our data also indicate that the proliferation of s upporting cells is related only to growth in surface area of the epith elium. No turnover seems to occur in the supporting cells as it does i n the olfactory neurons, where proliferation of basal cells is necessa ry for both growth and replacement. (C) 1998 Wiley-Liss, Inc.