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 Japanese quail are sensitive to the plasma levels of testosterone: their volume and optical density in Nissl-stained sections increase in castrated birds treated with testosterone. The present study was performed on castrated male quail treated or not with Silastic implants filled with testosterone to describe the ultrastructural variations induced by testosterone in these neurons. Gonadally intact male birds were included as controls. The ultrastructure of neurons, taken from the dorsolateral portion of the POM, was dramatically affected by the endocrine manipulations. Quantitative evaluations demonstrated a significant decrease in castrated birds of the rough endoplasmic reticulum (RER), of free polyribosomes, of Golgi complexes, and of dense bodies; these changes paralleled the decrease in cell size. The cell size and the percentage of volume occupied by the intracellular organelles in castrated birds treated with testosterone were comparable to values observed in controls. 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 involved in protein synthesis and secretion. In addition, exposure to testosterone affects the synaptic inputs to POM. These ultrastructural changes are presumably related to the physiological effects (e.g., activation of male sexual behavior) exerted by testosterone on this preoptic region.