Mating Stimulation Required for Mating-Induced Estrous Abbreviation in Female Rats: Effects of Repeated Testing Amy L. Bennett,* , † Meg E. Blasberg,* and Jeffrey D. Blaustein* ,1 *Center for Neuroendocrine Studies, Neuroscience and Behavior Program, University of Massachusetts, Amherst, Massachusetts 01003; and †Psychology Department, Division of Social Sciences, Concordia University, Ann Arbor, Michigan 48105 Received October 22, 2001; revised January 28, 2002; accepted January 29, 2002 Mating stimulation, particularly vaginal–cervical stimu- lation, causes estrous abbreviation in female rats. In most previous studies, female rats were repeatedly tested for sexual behavior until estrous termination oc- curred. Thus, it was not clear whether sensory stimula- tion (e.g., flank stimulation, olfactory cues) received dur- ing the repeated testing procedure contributed to estrous abbreviation. In Experiment 1, we determined the effect of premating to two or four ejaculations on the rate of estrous termination when a repeated testing pro- cedure was used. We compared ovariectomized, hor- mone-primed, female rats receiving (1) four ejaculations, (2) two ejaculations, or (3) no premating. Females pre- mated to either two or four ejaculations showed signif- icantly lower levels of sexual receptivity 12 h later than did nonpremated females. These results confirm that premating induces estrous abbreviation when a re- peated testing procedure is used. In Experiment 2, we determined whether the repeated testing procedure was necessary for estrous abbreviation. Ovariectomized, hormone-primed female rats were premated to two ejaculations or not premated. The rats were then tested for sexual behavior repeatedly or only once. Females that were premated and repeatedly tested for sexual behavior showed a statistically significant decrease in sexual receptivity compared to females that were not premated; however, the level of sexual receptivity in premated females did not differ from that in non-pre- mated females when they were tested only once. The results suggest that heat duration is the result of a com- plex interplay between those factors that promote the expression of sexual receptivity and those that inhibit it. © 2002 Elsevier Science (USA) In estrous cycling female rats, a gradual increase in estradiol levels followed by a peak in progesterone induces sexual behavior (Boling and Blandau, 1939; Powers, 1970). In one early study, the period of sexual receptivity lasted an average of 13.7 h (Blandau, Bol- ing, and Young, 1941). Although ovariectomy abol- ishes spontaneous estrus by removing the main source of these hormones, sexual behavior can be reinstated by sequential injections of estradiol and progesterone (Boling and Blandau, 1939). Many aspects of female sexual behavior are influ- enced not only by hormones, but also by the sensory stimulation that the female receives during mating. Although the female receives many types of sensory cues (e.g., olfactory, auditory, and tactile) during mat- ing, previous studies suggest that vaginal– cervical stimulation (VCS) received during intromissions and ejaculations is particularly important for inducing changes in sexual behavior and reproductive physiol- ogy. For example, VCS increases return latencies dur- ing paced mating (Yang and Clemens, 1997) and in- duces twice daily prolactin surges necessary to maintain pregnancy (Everett, 1964). The duration of sexual receptivity is also influenced by mating stimulation. In an earlier study, mating stimulation reduced estrous duration by about 3 h (Blandau et al., 1941). Like changes in return latencies and the induction of pseudopregnancy, estrous abbre- viation is believed to be induced specifically by VCS. Either transection of the pelvic nerve, a primary source of sensory afferents from the cervix (Lodder and Zeilmaker, 1976), or covering the vagina, which blocks the receipt of intromissions (Reading and Blaustein, 1984), prevents mating-induced estrous ab- breviation. Furthermore, females receiving experi- menter-administered VCS show behavioral changes 1 To whom correspondence should be addressed at, Center for Neuroendocrine Studies, Neuroscience and Behavior Program, To- bin Hall, 135 Hicks Way, University of Massachusetts, Amherst, MA 01003-9271. Fax: (413) 545-0769. E-mail: blaustein@cns.umass.edu. Hormones and Behavior 42, 206–211 (2002) doi:10.1006/hbeh.2002.1809 0018-506X/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved. 206