The paraventricular nucleus (PVN) of the hypothalamus, which is considered to be a centre for autonomic regulation, has been shown to exhibit physiological and functional sex differences. It is involved in numerous functions, from stress to the appetite, body energy balance, blood pressure, heart rate and sexual activity, including penile erection [1], and is characterised by a very complex architecture. OXT is produced chiefly by magnocellular neurosecretory cells in the PVN and supraoptic nucleus of the hypothalamus and released into the blood from the axon terminals in the neurohypophysis and into the surrounding neuropil from magnocellular dendrites [2,3]. The principal functions attributed to OXT are involved in the regulation of reproductive functions including parturition, milk ejection, and sexual and maternal behaviour in females, so called a feminine hormone (for review, see Ref. [4] ). On the other hand, it is well accepted that a group of OXT-ergic neurones originating in the PVN and projecting to extrahypothalamic areas (e.g., hippocampus, medulla oblongata and spinal cord) control penile erection and sexual behaviour in male rats [5]. It has been reported that OXT positively impacted on a number of components of sexual function, including libido, erection, and orgasm in men [6-8]. The intracerebroventricular administration of OXT also induced a dose-dependent increase in the number of penile erections and yawning episodes in male rats, suggesting a physiological role of hypothalamic OXT in the regulation of such responses [9]. Because penile erection and yawning induced by either OXT or apomorphine in rats were antagonised in a dose-dependent manner by pre-treatment with OXT antagonists, dopamine may induce these responses by releasing OXT in vivo [9].

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