Central ghrelin receptor stimulation modulates sex motivation in male rats in a site dependent manner
Ghrelin, a hormone produced primarily by the stomach, has been associated with motivational processes that include reward-seeking behaviors. In male laboratory mice, elevation of ghrelin levels enhances some aspects of sexual motivation and behavior, whereas in other experiments with male mice, rats, and other species, ghrelin treatment or food deprivation decreases sexual motivation and/or behavior. The present tested the hypothesis that stimulation of ghrelin receptors in different brain regions have opposite effects on male sexual motivation and behavior. To do this we examined appetitive and consummatory sex behaviors of male rats with a truncated ghrelin receptor (FHH-GHSRm1/Mcwi), and that of their WT (FHH) littermates. We also examined the effects of ghrelin or the ghrelin antagonist D-Lys-GHRP6 delivered into the VTA or the MPOA on appetitive and consummatory sex behaviors in male Long Evans rats. Results demonstrate that rats with a truncated ghrelin receptor, or rats that are food deprived, show deficits in anticipatory sex. Furthermore, although ghrelin does not further stimulate sex anticipation in rats when infused into the VTA, intra-VTA infusions of D-Lys-GHRP6 into the VTA further decreases in sex anticipation in food deprived rats. In contrast, ghrelin delivery into the mPOA decreased sex anticipation compared to saline or D-Lys-GHRP6 infused rats. Overall, these data suggest that ghrelin receptor signalling is important for full expression of appetitive sex behaviors. Within the VTA, ghrelin may act to enhance sex motivation, while acting on the mPOA to decrease sex motivation and promote foraging.