TESTOSTERONE EFFECTS ON THE NEURONAL ULTRASTRUCTURE IN THE MEDIAL PREOPTIC NUCLEUS OF MALE JAPANESE-QUAIL

Dorsolateral neurons of the medial preoptic nucleus (POM) of male Japa nese quail are sensitive to the plasma levels of testosterone: their v olume and optical density in Nissl-stained sections increase in castra ted birds treated with testosterone. The present study was performed o n castrated male quail treated or not with Silastic implants filled wi th testosterone to describe the ultrastructural variations induced by testosterone in these neurons. Gonadally intact male birds were includ ed as controls. The ultrastructure of neurons, taken from the dorsolat eral portion of the POM, was dramatically affected by the endocrine ma nipulations. Quantitative evaluations demonstrated a significant decre ase in castrated birds of the rough endoplasmic reticulum (RER), of fr ee polyribosomes, of Golgi complexes, and of dense bodies; these chang es paralleled the decrease in cell size. The cell size and the percent age of volume occupied by the intracellular organelles in castrated bi rds treated with testosterone were comparable to values observed in co ntrols. These ultrastructural changes are similar to those observed in neuronal targets for other gonadal hormones, supporting the idea that testosterone stimulates the development of cytoplasmic structures inv olved in protein synthesis and secretion. In addition, exposure to tes tosterone affects the synaptic inputs to POM. These ultrastructural ch anges are presumably related to the physiological effects (e.g., activ ation of male sexual behavior) exerted by testosterone on this preopti c region.