Sex-Related Differences in the Cell Cycle Parameters of the Ventricular Zone in the Developing Preoptic Area of Rat Embryos

The existence of functional and structural sex differences in the mammalian and human preoptic area (POA) and the anterior hypothalamus, where sexual dimorphism with respect to the nuclear volume, number of cells, and synaptic organization is particularly striking [3], has been firmly established [1‐5]. However, the specific mechanisms underlying sexual differentiation in the hypothalamus are still poorly understood, although they are generally believed to involve the dependence on gonadal steroids during development. In particular, one of the least understood aspects is the role of cell proliferation in the development of sexual dimorphism in the hypothalamus during early neuronogenesis. To elucidate the developmental mechanisms implicated in the sex-related alterations in the number of neurons in the mammalian hypothalamus, we focused our study on the possible sex differences in the cytokinetic behavior within the ventricular zone (VZ) of the embryonic rat POA that gives rise to the so-called sexual dimorphic nucleus of the preoptic area. This brain region was chosen for the study because of its intrinsic interest as an important component of the hypothalamic regulatory system involved in a variety of physiological mechanisms and behavioral responses, including reproductive behavior, and because it provides a unique opportunity to study the regulation of the number of neurons within the same structure of a single species, i.e., by comparing the two sexes. The specific goals were to determine whether there are regional and sex-related differences in: the duration of cell proliferation, the length of the overall cell cycle, and the lengths of the phases of the cell cycle.