Abstract

Oxytocin (OT) is known for its regulatory role in the formation of partner preference in the monogamous prairie vole. In contrast, female rats are considered promiscuous and typically copulate with many males during a mating bout. Despite this promiscuity, female rats selectively receive ejaculations from a dominant male and wait longer before resuming copulation following the receipt of a dominant male’s ejaculation, allowing for sperm transport. A preference to solicit and receive a particular male’s ejaculation can also be formed using Pavlovian conditioning in which females repeatedly pace copulation with males bearing a neutral scent cue. Pacing, the ability of a female to voluntarily initiate copulation and withdraw from a male, is known to be a potent sexual reward and facilitates pregnancy and reproductive responses. OT is known to regulate reproductive responses in female rats following copulation. The aim of the research in this thesis was to examine the role of OT in the formation of conditioned mate preferences, in addition to OT’s effects on reproductive responses. In the first chapter, females received their first copulatory experiences with the same male under one of two different pacing conditions. It was found that the pacing condition associated with longer pacing intervals resulted in a preference to receive a paired male’s ejaculation. Using immunohistochemistry, it was shown that preferred males activate OT neurons in three areas of the hypothalamus important for female sexual behaviours, the medial preoptic area, the ventromedial hypothalamus, and the paraventricular nucleus. The second chapter used a variety of behavioural and immunohistochemical assays to examine how OT transmission facilitates mate preference formation in rats. It was shown that peripherally-injected OT mimics the effects of vaginocervical stimulation (VCS) and facilitates mate preference formation. The effects of VCS were blocked by an OT receptor (OTR) antagonist that does not enter the brain, suggesting that peripheral OTRs are important for reproductive responses and preference formation following VCS. Taken together, these data indicate that OT transmission is required for sexual satiety, an important component of sexual reward, and early progestational responses, such as estrous termination. As such, these data suggest that sexual reward and enhanced reproduction are linked through Pavlovian processes that activate both central and peripheral OT.