The prenatal development of alkaline phosphatase activity in the hypothalamus of the rat

The localization of alkaline phosphatase (E.C. 3.1.3.1.) positivity during prenatal development of the hypothalamus of the rat is described. At E12 all layers of the prosencephalon display alkaline phosphatase (AP) positivity. The AP positivity increases from dorsal to ventral. Within the hypothalamic area a second, rostro-ventral gradient exists from E14 onwards. At E18 both gradients have decreased. At E20 almost all AP positivity has disappeared from the hypothalamus, with the exception of some reaction product in the dorsal ventricular matrix of the hypothalamus. The significance of this pattern in relation to the differentiation of the hypothalamus and to the formation of hypothalamic connections is discussed. It is suggested that AP activity is related to the formation of connections.