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In this study, in order to clarify the kinetics of leptin, we focused on the ratio ofLeptin acts as an afferent signal in negative feedback regulating body fat mass [6,7,16]. As body weight increases, leptin concentrations in the blood increase, causing appetite to decrease and energy consumption to increase via the hypothalamus. As a result, body fat decreases. Thus, leptin is part of the neuroendcrine system maintaining a balance between calorie intake and energy consumption.However, resistance to leptin has been observed via genetic mutations associated with adiposis. The action of leptin is based on signals from peripheral fat stores to the hypothalamus via the blood-brain barrier, stimulating the central nervous system (satiety center and sympathetic nerves). In this process, many factors are involved, and mutation of the b 3 -adrenalin receptor gene or the presence of leptin antibodies, for example, can obstruct leptin transport into cerebrospinal fluid from blood or eliminate leptin from the blood.

Purpose The dopamine-derived endogenous compound, R-salsolinol (SAL), was recently identified as a putative endogenous prolactin (PRL)-releasing factor. However, how SAL influences copulatory behavior is unknown. In this study, we examined the relationship between SAL and copulatory behavior in male rats. Methods Male Sprague-Dawley rats administered SAL were exposed to female rats in estrus, the plasma PRL concentration was measured, and the behavioral frequency and time during copulatory behavior were noted. ResultsIn the control and SAL groups, plasma PRL concentrations at 15 min before exposure to the female were 7.3 ± 2.0 and 8.0 ± 1.5 ng/ml, respectively. Moreover, plasma PRL concentrations in males immediately after exposure to the female were 7.4 ± 1.2 and 68.0 ± 5.9 ng/ml, respectively (P \ 0.05). All (8/8) of the control animals ejaculated in the presence of the female, whereas only 33% (2/6) of the SAL group ejaculated. An increasing tendency for mount latency and intromission latency and a decreasing tendency for intromission frequency were observed in the SAL group. Conclusions Copulatory behavior was inhibited in male rats after SAL injection, suggesting that SAL is a copulatory behavior inhibiting factor.