The development of in ovo odor sensitivity in chicks

The chick olfactory system in the embryo is known to attain function prior to hatching; the peripheral neurons develop function as early as embryonic day 13 (E13). To determine the specificity and critical period for development of odor sensitivity in chick olfactory central nervous system, different patterns of activation of the immediate early gene cFos in the olfactory bulb were determined. Chick embryos were exposed to amyl acetate, phenylethyl alcohol, or no odor for 3 day periods from E14 through E20; cFos immunoreactivity was examined to determine olfactory bulb activation as a result of odorant exposure. Staining patterns for each animal exposed to amyl acetate versus phenylethyl alcohol and those from chicks exposed to the same odorant over different time periods were compared. cFos staining patterns suggested differences in odorant-elicited bulbar activation occur from E15 through E18 further suggesting that the critical period for the development of odor sensitivity occurs at this time. This highlights the importance of the sensory environment in shaping the developmental pathways of the olfactory system