Abstract
A continuously increasing amount of research shows that oxytocin is involved in numerous central functions. Among the functions in which oxytocin is thought to be involved are those that play a role in social and sexual behaviors, and the involvement of central oxytocin in erectile function and sexual behavior was indeed one of the first to be discovered in laboratory animals in the 1980s. The first part of this review summarizes the results of studies done in laboratory animals that support a facilitatory role of oxytocin in male and female sexual behavior and reveal mechanisms through which this ancient neuropeptide participates in concert with other neurotransmitters and neuropeptides in this complex function, which is fundamental for the species reproduction. The second part summarizes the results of studies done mainly with intranasal oxytocin in men and women with the aim to translate the results found in laboratory animals to humans. Unexpectedly, the results of these studies do not appear to confirm the facilitatory role of oxytocin found in male and female sexual behavior in animals, both in men and women. Possible explanations for the failure of oxytocin to improve sexual behavior in men and women and strategies to attempt to overcome this impasse are considered.
Highlights
Oxytocin is the neurohypophyseal peptide that is well known for its hormonal role in lactation and parturition and was discovered and synthesized together with the other neurohypophyseal peptide arginine-vasopressin in the 1950s by the Nobel Price Du Vigneaud and coworkers [1,2]
In line with this hypothesis, (i) oxytocin injected into the caudal ventral tegmental area at a dose that induces penile erection increased extra-cellular dopamine in the dialysate obtained from the nucleus accumbens and from the PVN [171], and (ii) these effects are eliminated by the prior injection of the oxytocin receptor antagonist d(CH2 )5 -Tyr(Me)2 -Orn8 -vasotocin into the caudal ventral tegmental area or by the injection of haloperidol into the nucleus accumbens [88,171]
Intracerebral microdialysis experiments show that in male rats, oxytocin injected into the ventral subiculum at doses that induce penile erection increases NO production and extra-cellular glutamic acid in the dialysate obtained from the ventral subiculum [180] and of extra-cellular dopamine in the nucleus accumbens and medial prefrontal cortex [180,181]
Summary
Oxytocin is the neurohypophyseal peptide that is well known for its hormonal role in lactation and parturition and was discovered and synthesized together with the other neurohypophyseal peptide arginine-vasopressin in the 1950s by the Nobel Price Du Vigneaud and coworkers [1,2] (see Table 1 for the amino acid sequence of neurohypophyseal peptides and a few of their peptidic and non-peptidic analogues). Since the first pioneering studies conducted in the 1960s that showed a facilitatory effect of oxytocin on male sexual behavior by revealing that intravenous-systemic oxytocin was either capable of decreasing the latency to the first ejaculation and of retarding the sexual exhaustion of male rabbits paired with a receptive female [53] as well as of ameliorating psychogenic impotence in a limited number of human patients [54], numerous other studies have confirmed that oxytocin is deeply involved in erectile function and copulatory behavior. No method was used to validate and/or summarize the evidence for and against the facilitatory role of oxytocin in erectile function and sexual behavior given by the selected studies
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