Effects of α‐Melanocyte‐Stimulating Hormone on Magnocellular Oxytocin Neurones and their Activation at Intromission in Male Rats

Abstract

The peptides alpha-melanocyte-stimulating hormone (alpha-MSH) and oxytocin have very similar effects on several behaviours, including male sexual behaviour. Both induce penile erection and enhance copulatory behaviour when given centrally, suggesting that their central actions are not independent. Here, we used intromission as a physiological stimulus to investigate whether some central effects of alpha-MSH during male sexual behaviour are mediated by oxytocin neurones. We used the expression of the immediate-early gene product Fos to investigate oxytocin neurone activation at intromission and after intracerebroventricular (i.c.v.) administration of alpha-MSH (1 microg/5 microl) and studied the effects of i.c.v. administration of a MC4 receptor antagonist on Fos expression and on the latency of male rats to exhibit sexual behaviour in the presence of a receptive female. In rats that showed intromission, Fos was expressed in magnocellular oxytocin neurones in both the paraventricular nucleus (PVN) and the supraoptic nucleus (SON), but there was no significant activation of parvocellular oxytocin neurones of the PVN. Similarly, alpha-MSH increased Fos expression in magnocellular oxytocin neurones but had little or no effect in parvocellular oxytocin neurones. In male rats that achieved intromission, central injection of a MC4 receptor antagonist significantly attenuated the increase in Fos expression in magnocellular oxytocin neurones in both the PVN and the SON and increased mount and intromission latencies compared to vehicle-injected controls. Together, the results indicate that magnocellular oxytocin neurones are involved in the central regulation of male sexual behaviour, and that some of the central effects of alpha-MSH are likely to be mediated by magnocellular oxytocin neurones.

The anorexigenic and hypertensive effects of nesfatin-1 are reversed by pretreatment with an oxytocin receptor antagonist

“…Intracerebroventricular administration of the melanocortin ¾ receptor agonist, ␣-MSH led to c-Fos accumulation in oxytocin-producing neurons (6). Pretreatment with OVT reversed the anorexigenic effect of leptin (3), a peptide that is dependent on the central melanocortin system to exert its activities (9).…”

Mechanisms of Penile Erection and Basis for Pharmacological Treatment of Erectile Dysfunction

“…However, NO seems to be involved in the adrenocorticotropin effects (Poggioli et al, 1995). Magnocellular oxytocin neurons were found to be involved in the central regulation of male sexual behavior, and some of the central effects of ␣-MSH are likely to be mediated by magnocellular oxytocin neurons (Caquineau et al, 2006).…”

Neural Substrates Underlying Interactions between Appetite Stress and Reward

“…For example, the arcuate nucleus contains a population of neurones that is the main source of the key anorexigenic peptide alpha melanocyte stimulating hormone (αMSH); this, signalling mainly through hypothalamic MC4 receptors, is a very potent inhibitor of feeding and was a major target of efforts to develop pharmaceutical approaches to moderating appetite. However, the same neurones, again acting via αMSH release and its effects on MC4 receptors, are also a potent stimulator of sexual behaviour [9]. It seems likely that the motivation to eat and the motivation to reproduce, being mutually exclusive, are reciprocally regulated – so any attempt to intervene pharmacologically at this level may have important consequences for other behaviours.…”