Projection from the estrogen receptor-rich region of the hypothalamus to other estrogen receptor-containing sites in the female guinea pig brain

Sexual behavior in female guinea pigs and rats is dependent upon circulating ovarian steroid hormones. The actions of these hormones on behavior are mediated by intracellular receptors located within interconnected brain regions. This complex neural network integrates somatosensory and hormonal information relevant to sexual behavior. An understanding of the anatomy of this network is important for understanding how behavior is generated. This dissertation investigated the neural projections from a region important for the induction of sexual behavior, the ventrolateral hypothalamus. Based on the steroid-sensitive neural network model described in rats, several experiments were designed to test predictions of this neural model in guinea pigs. In the first experiment, estrogen receptor- and estradiol-induced progestin receptor-containing cells were localized in the midbrain, a major projection site of the steroid receptor-rich region within the ventrolateral hypothalamus. In the second experiment, the anterograde tracer Phaseolus vulgaris-Leucoagglutinin, an anterograde tract-tracer, was deposited within the estrogen receptor-containing region of the ventrolateral hypothalamus. Projections from this area were found in most other estrogen receptor-containing sites, including the midbrain central gray, often closely associated with estrogen receptor-containing cells. The third experiment examined the distributions of substance P, a peptide found in ovarian steroid hormone receptor-containing cells in the ventrolateral hypothalamus and estrogen receptor-containing cells in the midbrain central gray. Substance P-immunoreactive boutons were found closely associated with some estrogen receptor-containing cells suggesting substance P modulation of ovarian steroid hormone receptor-containing cells. These connections, taken together with the hypothalamic projections closely associated with estrogen receptor-containing cells in the midbrain, support the idea that some estrogen receptor-containing cells may be directly linked. These studies provide information on the neural connections between estrogen receptor-containing regions and cells which may be important for regulating functions of the steroid hormone sensitive neural network