Nerve growth factor-mediated sexual differentiation of the rat hypothalamus

Injection of antibody to nerve growth factor into the cerebral lateral ventricle blocked testosterone-induced behavioral defeminization of neonatal female rats. When tested as adults following ovariectomy and combined estrogen-progesterone treatment, the injected animals showed a significantly higher lordosis quotient than the testosterone-treated, normal rabbit serum-infused controls. Failure of vaginal opening and clitoral enlargement manifested the well-documented masculinizing effect of testosterone on the genitalia in the experimental as well as the control animals. Estrogen sensitivity of hypothalamic neurons which are responsible for the induction of lordosis was retained in the experimental animals. Recordings of the antidromic action potentials from neurons in the ventromedial nucleus of the hypothalamus following stimulation of the midbrain central gray revealed that estrogen decreased the antidromic activation threshold and shortened the absolute refractory period of the hypothalamic efferents along with the estrogen-induced behavioral activation in the experimental animals. In the control group, the estrogen-induced neuronal activation was lost altogether with the behavioral activation.