Stimulus access to the accessory olfactory system in the prenatal and perinatal rat

The fetal rat can detect odors in its amniotic fluid. Indirect evidence suggests that the accessory olfactory system may be mediating chemoreception prenatally. The primary goal of this study was to determine if stimuli in the amniotic fluid gain access to the receptor neurons of the accessory olfactory system that are sequestered inside the vomeronasal organ. Other goals of the study were to compare the access of stimuli to the vomeronasal organ in the prenatal and young postnatal rat and to examine the role of the autonomic nervous system in this process. On the day before birth fluorescent beads (0.95 microns diameter) were injected into the amniotic sacs of rat fetuses from seven dams. After 4-6 h one group of mothers received an i.p. injection of epinephrine (either 60 or 75 micrograms) and another group received no injection. One hour later pups were collected and processed for histological examination using fluorescence microscopy. A portion of the fetuses from both treatment groups had significant numbers (< 50) of beads in their nasal passages. Some of these subjects also had beads in the vomeronasal organ. There was no significant difference in the proportion of subjects with beads in the nasal cavities or vomeronasal organ across the two treatments. In a second experiment, five- to seven-day-old rat pups had beads infused into one naris. After 3-4 h one group was injected i.p. with epinephrine (2-4 micrograms), while a second group received no injection. As expected, virtually all the subjects had large numbers of beads in their nasal cavities upon post mortem examination.(ABSTRACT TRUNCATED AT 250 WORDS)