ReviewNeurobiology of sexual behavior
Introduction
Substantial progress has been made in elucidating the neuroanatomical, neuroendocrine and neurochemical regulation of appetitive and consummatory aspects of sexual behavior. This effort has been aided by the addition of new behavioral paradigms, animal models of drug-induced human sexual dysfunction, and correlative work in humans, especially in the area of brain and hormonal activation by sexual stimuli. This review, which is by no means complete, attempts to provide a framework for some of the exciting research findings that have appeared since August 1998.
Section snippets
Behavioral paradigms
A ‘triad mating paradigm’ was introduced [1••] in which a single male rat is placed into an open field with two sexually receptive female rats. Males trained previously to associate a neutral odor (almond or lemon) with sexual activity ejaculated preferentially with females bearing that odor, despite copulating indiscriminately with both females (Figure 1). This conditioned ejaculatory preference was Pavlovian in nature, as males in random- and explicitly-unpaired control groups did not show
Animal models of human sexual dysfunction
Antidepressant and antihypertensive medications in humans are notorious for their sexual side effects, including the disorders of sexual desire, arousal and orgasm. Sub-chronic and chronic effects of fluoxetine (Prozac, Eli Lilley Incorporated, Indianopolis, USA) have been examined in sexually active female [2] and male [3•] rats. Daily fluoxetine administration for one to three weeks reduced lordosis quotients in gonadally intact females in estrus without altering vaginal cyclicity. A similar
Stimulation of sexual desire and arousal
Neural mechanisms associated with motivational aspects of sexual behavior, including the stimulation of erection and ejaculation in sexually active rats, or the stimulation of copulation in sexually sluggish or naive rats, have been examined. Several studies have refined our understanding of the regulation of noncontact erections (NCEs) in male rats, a homologue of psychogenic erection in humans that is stimulated by sex odors from the female. In sexually experienced, castrated male rats, NCEs
Copulation and sexual stimulation
Specific effects of drugs and hormones on consummatory measures of copulation continue to be an important focus of research, as do studies that reveal neuroanatomical activation following particular types of sexual stimulation.
Serotonin (5-HT) systems have been examined, with particular regard to the facilitation of ejaculation produced by the 5-HT1A agonist 8-OH-DPAT. Interactions with DA systems have been examined both in the mPOA [25] and systemically [26]. Regarding female sexual behavior,
Human sexual behavior
Several advances have been made in understanding the relationship between plasma hormone levels and sexual desire, arousal and stimulation. Monthly measures of salivary testosterone were correlated positively with the initiation and rate of sexual intercourse in adolescent males [44•]. In aging males, however, the androgen dihydroepiandrosterone (DHEA), much publicized for its ability to improve sexual function and general sense of well-being, had only transient effects in a well-controlled,
Conclusions
The introduction of Viagra (Pfizer, UK) in 1998 marked a resurgence of interest in the neurobiology of sexual function and dysfunction. Thanks to years of progress in understanding basic brain, hormonal and neurochemical mechanisms of copulatory behavior, and recent advances in molecular biology and pharmacology, we stand at a crossroads in the study of sexual behavior. Trends in the past year indicate that more appetitive aspects of sexual desire and arousal are being studied in laboratory
Acknowledgements
The work from the author’s laboratory reported in this review was supported by grants from the Medical Research Council of Canada (MT-13125), Natural Sciences and Engineering Research Council of Canada (OGP-0138878), and Fonds pour la Formation de Chercheurs et l’Aide à la Recherche du Québec (CE-98). The author would like to acknowledge the scientific contributions of James Cantor, Tod Kippin, Wendy Smith, and Carol Coopersmith.
References and recommended reading
Papers of particular interest, published within the annual period of review, have been highlighted as:
• of special interest
•• of outstanding interest
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