Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Anatomy and Cell Biology


Dr. Lique M. Coolen


Sexual behavior in male rats is a complex rewarding behavior and many neurotransmitters and neuropeptides play an important role in mediation of sexual performance, motivation and reward. The hypothalamic neuropeptide orexin has been shown play a key role in reward associated with food and drugs of abuse, but the role of this neuropeptide in control of sexual performance, motivation and reward is currently unclear. First, it was shown that orexin neurons in the hypothalamus are activated during sexual performance and reward. Next, using cell specific lesions of orexin neurons it was demonstrated that orexin is involved in arousal and anxiety, but is not critical for sexual performance or motivation. Moreover, orexin was shown to play a critical role in control of sexual reward. Thus, these studies provided novel information regarding a role for orexin in this natural reward behavior. Recent studies have shown that sexual behavior in male rats causes neuroplasticity in the mesolimbic system, enhanced psychostimulant-induced locomotor activity and drug craving. The latter of which is dependent on a period of abstinence from sexual behavior, suggesting an increased vulnerability for addiction following loss of sexual reward. Thus, the next goal of this thesis determined if abstinence from sexual behavior also leads increased vulnerability for other disorders related to reward processing, specifically depression-like behavior. It was demonstrated that a prolonged (28 day) but not short (1 or 7 day) period of abstinence causes depression-like behavior in sexually experienced male rats seen as increased passive stress coping behaviors and anhedonia. Development of depression-like behavior was associated with increased levels of corticotropin releasing factor mRNA in the paraventricular nucleus of the hypothalamus and increased hypothalamic-pituitary-adrenal axis activity in response to an acute stressor. Thus, these studies provide novel information on behavioral and neuroplastic alterations observed following a prolonged period of abstinence from mating and suggest that loss of sexual reward in male rats may be a paradigm to study depression following loss of social reward in humans.