The effect of castration upon the ultrastructure of the rat hypothalamus

Summary The arcuate complex, comprising the nucleus and the outer zone of the median eminence, was studied under the electron microscope in control and castrated rats of both sexes. One month after castration the arcuate neurons show signs of hyperactivity characterized by dilated cisternae of the endoplasmic reticulum, a large nucleolus, situated near the nuclear envelope and fewer granulated vesicles. The surrounding neuropile shows an increase in the number of granulated vesicles above the control level. Six months after castration the changes already described are more accentuated. In the outer zone of the median eminence the axons and terminals show a considerable increase in the number of granulated vesicles which is of the order of 50 per cent above the control. A correlation between the granulated vesicles and the high content in dopamine of the arcuate complex is postulated. The ultrastructural changes observed in the arcuate complex, after castration, are discussed in relation to the current knowledge on the histophysiology of this region of the hypothalamus and specially on the probable regulatory effect of monoamines on the secretion of gonadotrophins.Supported by grants from the Consejo Nacional de Investigaciones Cientificas y Técnicas and by the Air Force Office of Scientific Research (AF-AFOSR 963-67).We are deeply indebted to Mrs. Defilippi-Novoa and Mr. Alberto Saenz for their skilful assistence.