Recent evidence suggests that the accessory olfactory system (AOS) may mediate chemoreception before birth. Such a capability may allow the fetus to begin to sample chemical stimuli from the outside world, a possibility that has important developmental and evolutionary implications. Herein we describe the development in the mouse of the duct that connects the vomeronasal organ (VNO), containing the primary receptor neurons of the AOS, with the nasal cavity and thus with external stimuli. Twenty-four mice, four at each of six different ages from the last day of gestation through 25 days of age, were fixed and embedded in glycol methacrylate. Serial sections were examined under the light microscope so that the VNO duct could be reconstructed in three dimensions. Results confirm an earlier study which demonstrated that the VNO duct is not patent before birth. The duct becomes patent sometime after the first day of life but remains in an immature condition throughout the normal prepubertal period. During this period the duct is characterized by an internal surface that is rapidly desquamating such that the lumen of the duct contains sloughed tissue. These results suggest that the VNO is unlikely to function in the prenatal period, since the route for external stimuli to reach its receptor surface is blocked. The protracted period of VNO duct development reported here is consistent with the great bulk of data on the AOS of mammals which firmly establishes its role in the detection of pheromones which coordinate reproduction.

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