Facilitation of tonic immobility by stimulation of the vaginal cervix in the rat

Stimulation of the vaginal cervix with a plunger from a 1 cc syringe induced tonic immobility (i.e., blocked gross movement including the righting reflex) in response to inversion combined with brief manual restraint, in otherwise insusceptible female rats. In a second experiment, estradiol benzoate administration potentiated this effect somewhat, as measured by the latency to immobilization, although the duration of immobility was not significantly affected. Results are discussed in terms of the possible relationship between tonic immobility and lordosis, the immobile mating posture of the female rat, which is also potentiated by cervical stimulation.