Neural inputs from the uterus to the paraventricular magnocellular neurons in the rat.

Extracellular action potentials were recorded from antidromically identified, tonically firing cells in the hypothalamic paraventricular nucleus (PVN) of ovariectomized, estrogen-treated female rats under urethane anesthesia. Genital or somatic sensory stimuli, or electrical stimulation of the nerves innervating the pelvis were applied. Uterine horn or vaginal distension each excited 33% of the neurons tested. Probing of the cervix had no effect. Hindpaw pinch produced excitation in 39% and inhibition in 11% of the neurons tested. Non-noxious somatic stimuli had no effect. Stimulation of the uterine afferent nerves, the hypogastric and pelvic nerves, excited 55% and 30% of the neurons tested, respectively. Stimulation of a somatic nerve of the hindleg, the sciatic nerve, activated 80% of the neurons tested. These results indicate that specific sensory afferents arrive at the PVN from the uterus; in addition, somatic afferents converge in this hypothalamic nucleus.