NELSEN, MC; DAWLEY, EM; Ursinus College, Collegeville, PA: Seasonal Chemoreceptor Birth and Death

The olfactory epithelium of vertebrates includes stem cells that generate new receptor cells throughout life, presumably to replace damaged cells. However, the chemosensory system of red-backed salamander, Plethodon cinereus changes on a seasonal basis. An increase in size of the main olfactory and vomeronasal organs in early summer is a result of a spurt of cell division of stem cells while a decrease in size in late summer of these organs appears to be the result of apoptosis. We traced the fate and life span of these new receptor cells by injecting animals with BRDU (5-bromo-2�-deoxyuridine), which is incorporated into the DNA of cells during DNA synthesis, and sacrificing them at various time intervals after injection. We used immunocytochemistry to locate cells that had arisen from cell division since BrdU injection. We also examined programmed receptor cell death at various intervals using TUNEL (terminal deoxynucleotidyl transferase mediated dUTP-nick end labeling). Olfactory and vomeronasal receptor cells generated during the early summer remained in their respective epithelia for several months, indicating an extended life span for these cells and suggesting that they do become functional receptor cells. We found evidence of apoptotic cells in the olfactory epithelium of salamanders at every collection date, but there was a spike of apoptotic activity in animals collected in July. Thus, we suggest that receptor cells are generated seasonally to supplement the chemosensory epithelia and heighten chemosensory mediated behaviors.