UBC Theses and Dissertations
Effects of serotonin type 3 receptor activity on receptive and proceptive behaviours in female rats Tanco, Sheryl Anne
The neurotransmitter serotonin (5-HT) influences many centrally-mediated behaviours. In female rats, 5-HT affects the expression of lordosis, a behavioural index of sexual receptivity. Conflicting empirical evidence regarding the role of 5-HT, with respect to lordosis, and identification of subtypes of central 5-HT receptors led to formulation of the hypothesis that 5-HT plays a dual role with respect to female sexual behaviour. Evidence suggests that 5-HT₁[symbol omitted] receptors inhibit, while 5-HT₂ receptors facilitate lordosis. The recently identified central 5-HT₃ receptor affects the release of neurotransmitters such as dopamine, norepinephrine and acetylcholine; modulates the effects of opiates, amphetamine and nicotine; and influences anxiety, learning, nociception, nausea and vomiting. It remains to be determined whether 5-HT₃ receptors also influence reproductive activity. In female rats sexual activity is comprised of two types of behaviours: receptive (lordosis) and proceptive (ear wiggling, hopping and darting). In the current literature, lordosis stands as the primary measure; proceptive behaviours are seldom reported. The purpose of this thesis is to further characterize the 5-HT₃ receptor with respect to female reproductive activity and to increase the understanding of neurochemical factors which influence receptive and proceptive behaviours in female rats. The current series of experiments investigated the effects of 5-HT₃ agonists and antagonists, administered alone and in conjunction with morphine and apomorphine, on sexual behaviours in ovariectomized, steroid-primed female rats. The 5-HT₃ antagonists MDL 72222, ondansetron and ICS 205-930 failed to affect receptive or proceptive behaviours, although a trend towards a facilitatory effect was evident in the case of ondansetron. Similarly, the 5-HT3 agonists 1-phenylbiguanide and 2-methyl-serotonin, administered intracerebroventricularly, did not significantly influence female copulatory behaviours. While low doses of morphine significantly inhibited sexual activity, this inhibition was not attenuated by any of the 5-HT₃ antagonists. Likewise, apomorphine profoundly inhibited both receptive and proceptive behaviours, but these effects were not antagonized by ICS 205-930. Although these data do not support the idea that 5-HT3 receptors are influential in the modulation of female reproductive behaviours, consideration of various pharmacological and methodological factors caution against a premature conclusion in this regard.