SEX-DIFFERENCES IN THE DISTRIBUTION AND PROJECTIONS OF TESTOSTERONE TARGET NEURONS IN THE MEDIAL PREOPTIC AREA AND THE BED NUCLEUS OF THE STRIA TERMINALIS OF RATS

Retrograde tracing was combined with steroid hormone autoradiography t o investigate the projections of testosterone-target neurons in preopt ic and limbic regions to the midbrain in male and female rats. Autorad iograms were prepared from the brains of male and female rats that had received an injection of a fluorescent retrograde tracer into the mid brain, and an intravenous injection of [H-3]testosterone. Testosterone target neurons that project to the midbrain were abundant in the medi al preoptic nucleus (MPN) and bed nucleus of the stria terminalis (BST ) and were also observed in the ventromedial nucleus of the hypothalam us. Testosterone target neurons and testosterone target neurons that p roject to the midbrain were more abundant in the caudal half of the MP N compared to the rostral half. Moreover, male rats had more testoster one target neurons in the caudal MPN than female rats, and the number of testosterone target neurons in the MPN that project to the midbrain was higher in male than in female rats. Male rats also had more testo sterone target neurons than females throughout the encapsulated subdiv ision of the BST. We hypothesize that sex differences in the neuronal connectivity of testosterone target neurons may underly sex specific b ehavioral responsiveness to androgens, (C) 1994 Academic Press, Inc.