Postnatal development and sexual differentiation of pig hypothalamic nuclei.

The postnatal development of some nuclei in the hypothalamus of the pig is described in relation to sexual differentiation. The vasopressin and oxytocin containing nucleus (VON), a nucleus that has only been described in the pig to date, showed a twofold increase in neuron number and volume during puberty in both sexes. After puberty, this increase in neuron number continued in the females, resulting in a VON that is twice as large in females as in males. The supraoptic nucleus (SON) does not show an increase in neuron number during puberty but in females an increase after puberty is seen, resulting in a sexual dimorphism of the SON in adulthood. Experiments showed that the number of neurons of the VON can be influenced by gonadal steroids. This study confirms that sexual differentiation of the hypothalamus occurs much later in the pig than reported in any other mammalian species so far.