Journal of Comparative and Physiological Psychology 1975, Vol. 89, No. 1, 79-85 Vaginal Stimulation in Rats Induces Prolonged Lordosis Responsiveness and Sexual Receptivity Jorge F. Rodriguez-Sierra, William R. Crowley, and Barry R. Komisaruk Institute of Animal Behavior, Rutgers—The State University Sexual receptivity to males resulted from stimulation of the vagina with a glass rod in previously unreceptive ovariectomized, estrogen-treated rats. Several minutes of rejection behavior preceded the receptivity. In a second study, manual palpation was used to determine the duration of the lordosis response facilitation. Initially, all females were unresponsive to manual flank-perineum stimulation (palpation). Vaginal stimulation plus palpation, which together elicit lordosia, facilitated subsequent lordosis responses to palpation. This effect persisted for several hours after the vaginal stimu- lation was applied. Vaginal stimulation alone, which was ineffective in eliciting lordosis, also facilitated lordosis in response to subsequent palpa- tion. Repeated palpation did not facilitate lordosis. These prolonged effects were independent of hormone treatment. Enhancement of female mating behavior in response to repeated mating attempts by males has been indicated in several studies (Anderson, 1936; Beach, 1948; Clemens, Hiroi, & Gorski, 1969; Green, Luttge, & Whalen, 1970; Koster, 1943; Larsson, Feder, & Komisaruk, 1974). Although direct evi- dence regarding the stimulus factors in- volved in this enhancement of receptivity is lacking, this effect may be due in part to genital tract stimulation resulting from in- tromissions. Females maintain the lordosis posture longer after mounts with intromis- sions or ejaculation than after mounts with- out intromissions (Diakow, 1975; Kuehn & Beach, 1963), and denervation of the genital tract prevents this prolongation of lordosis following intromissions (Diakow, 1970). This paper is contribution No. 167 from the Institute of Animal Behavior. We gratefully ac- knowledge the excellent technical assistance of Ellen Azevedo. This research was supported by U.S. Public Health Service Research Grant MH- 13279 and by funds provided by the Alfred P. Sloan Foundation. Bibliographic aid was received from the University of California at Los Angeles Brain Information Service, which is a part of the National Information Network of the National Institute of Neurological Diseases and Blindness, and was supported under Contract PH-43-66-59. The estradiol benzoate was generously provided by A. Watnick and P. Perlman of the Schering Corp., Bloomfield, New Jersey. Requests for reprints should be sent to J. F. Rodriguez-Sierra, Institute of Animal Behavior, Rutgers University, 101 Warren Street, Newark, New Jersey 07102. Artificial genital tract stimulation (prob- ing the vaginal cervix with a glass rod) strongly facilitates lordosis in response to manual stimulation of the flanks and peri- neum (Komisaruk & Diakow, 1973). In that study, there was a suggestion that the effects of genital tract stimulation outlasted the actual application of the stimulus, because palpation of the flanks and perineum induced lordosis several minutes after, but not be- fore, genital tract stimulation. In the present study, we attempted to determine: (a) whether genital tract stimu- lation with a glass rod could make unrecep- tive female rats receptive to mating attempts by males, (b) how long after the cessationof this genital tract stimulation the lordosis- potentiating effect persists, and (c) the stimulus factors involved in the persistent facilitation of lordosis responding. EXPEKIMENT 1 Method Subjects. Forty-six Sprague-Dawley (Charles River Co., North Wilmington, Massachusetts) fe- male rats (200-250 gm.) were used. Animals were individually housed and maintained on a reverse day/night cycle (dark: 10:00-20:00) and provided with food and water ad lib. Procedure. One week after bilateral ovariec- tomy, all animals were injected with estradiol benzoate (EB) dissolved in sesame oil (5 Mg/kg; sc) for 2 consecutive days. This injection proce- dure had been determined to be subthreshold for inducing sexual receptivity in most females in preliminary observations. Mating tests were con- 79