OLFACTION IN-UTERO - BEHAVIORAL-STUDIES OF THE MOUSE FETUS

On the day before birth, mouse fetuses were tested for their behaviora l responses to iso-amyl acetate and iso-valeric acid delivered into th e nasal cavity in liquid phase. Pilot studies established that most su bjects responded to most concentrations used with an increase in total behaviors and number of different behaviors displayed. When iso-amyl acetate was systematically delivered at three concentrations (10(-3) M , 10(-4) M and 10(-5) M) subjects showed significant responses to each . In contrast, responses were not evident when saline was the stimulus , The magnitude of the average behavioral response did not decline wit h decreasing concentration of odorant. In a second experiment, the abi lity of the fetus to discriminate between iso-amyl acetate and iso-val eric acid was studied. Results establish that the fetuses responded di fferently to the two odorants. Given the immaturity of the mouse's acc essory olfactory system before birth and the observed responses to con centrations of odorants below the threshold of the trigeminal system, the results suggest that the mouse fetus has a functionally competent main olfactory system including the ability to discriminate between pu rified odorants. The results are discussed in terms of current models of chemosensory ontogeny. (C) 1997 Elsevier Science B.V.