Neurogenesis in the vomeronasal epithelium of adult garter snakes. 1. Degeneration of bipolar neurons and proliferation of undifferentiated cells following experimental vomeronasal axotomy

Abstract

Postnatal cell proliferation, presumably for the purpose of neuronal replacement, was demonstrated in the vomeronasal epithelium of adult garter snakes using experimental vomeronasal axotomy. The luminal supporting cell layer of the epithelium did not undergo mitosis, nor necrosis, but exhibited some morphological modifications following axotomy. The bipolar layer underwent progressive irreversible degeneration following denervation. Degeneration of neurons progressed initially from alteration of cellular ultrastructure, to gross distortion of neuronal shapes followed by disintegration and disappearance of necrotic neurons. Maximal depletion of neurons occurred two weeks following surgery. The columnar epithelium at that time was characterized by the presence of a cell-depleted zone located between the luminal supporting cell layer and the basal, undifferentiated (Ud) cell layer. This cell-depleted zone occupied 70-80% of each degenerated cell column. Regeneration of axotomized neurons did not occur. The basally located, Ud cells exhibited no changes indicative of necrotic processes, but underwent active cell proliferation following axotomy. Changes in proliferative properties in the Ud cell layer were temporally related to the degeneration of the neuronal cell layer following nerve lesion. The Ud cell proliferation rate was slower than the rate of Bp cell degeneration. Proliferating Ud cells in the denervated epithelium may serve as the source of reconstituted vomeronasal bipolar neurons.