Proliferation in the vomeronasal organ of the rat during postnatal development

We investigated proliferation of sensory cell precursors in the rat vomeron asal organ (VNO) at various postnatal ages from birth (P1) to P666, In the rat, which continues to grow during most of its adult life, proliferation m ight be related to growth and/or replacement. Proliferating cells were labe lled by BrdU injection, and histological sections of the VNO were evaluated after immunohistochemical detection of BrdU, Proliferation density (number of proliferating cells/section) decreased dramatically from 115 at P1 to 2 7.2 at P21, although the area increased. Adult values were reached at P66-P 333 (10.3 cells/section); at P400-P666 the value was 8.6 cells/section. Dis tribution of labelled cells changed considerably with age: in neonates the cells were nearly equally distributed throughout the sensory epithelium, wh ereas from P21 onwards most proliferating cells were concentrated in cluste rs near the boundaries with non-sensory epithelium. Labelled cells in the s ensory neuronal layer were adjacent to the undulating basement membrane-bor dering capillaries that intrude into the sensory epithelium, indicating tha t they were true basal cells, The volume of the sensory epithelium increase d between P1 and P66, and remained constant thereafter, although the length still increased. Length and volume of the sensory epithelium were related to body size, not to sex; males and females of the same body size had the s ame VNO size. The complex changes in proliferation pattern during postnatal development indicate differential growth and replacement. We suggest that in adults the labelled cell clusters near the boundaries are a pool for gro wth. whereas proliferation in the central parts represents a replacement po ol.