The Hypothalamic Neurosecretory Activity During the Oestrous Cycle, Pregnancy, Parturition, Lactation, and Persistent Oestrus, and After Gonadectomy, in the Rat

Abstract

The neurosecretory activity in the magnocellular supra-optic and paraventricular nuclei (SON and PVN) of the rat was studied during the course of pregnancy, parturition, and lactation, during the oestrous cycle and persistent oestrus, and following gonadectomy. The parameter for neurosecretory activity in this investigation is the distribution of the Golgi-apparatus specific enzyme, thiamine diphosphate-phosphohydrolase (TPP-ase), as measured by a semi-quantitative histochemical method. The SON and PVN react simultaneously under all the experimental conditions mentioned above. A peak in neurosecretory activity occurs at about mid-pregnancy in both magnocellular nuclei. A high neurosecretory activity is seen during and shortly after parturition and during lactation. A rapid rise in neurosecretory activity occurs in the SON and PVN as early as two weeks after gonadectomy. During the course of the oestrous cycle, high neurosecretory activity is seen during oestrus. During light-induced persistent oestrus, a high neurosecretory activity is seen in both nuclei. The existence of a close relationship between the blood level of gonadotropic hormones and the neurosecretory activity in the SON and PVN is discussed.