Mesolimbic leptin signaling negatively regulates cocaine-conditioned reward

The regulatory mechanisms underlying the response to addictive drugs are complex, and increasing evidence indicates that there is a role for appetite-regulating pathways in substance abuse. Leptin, an important adipose hormone that regulates energy balance and appetite, exerts its physiological functions via leptin receptors. However, the role of leptin signaling in regulating the response to cocaine remains unclear. Here we examined the potential role of leptin signaling in cocaine reward using a conditioned place preference (CPP) procedure. Our results showed that inhibition of leptin signaling by intracerebroventricular infusion of the leptin receptor (LepR) antagonist SMLA during cocaine conditioning increased the cocaine-CPP and upregulated the level of dopamine and its metabolites in the nucleus accumbens (NAc). We then selectively knocked down the LepR in the mesolimbic ventral tegmental area (VTA), NAc core and central amygdala (CeA) by injecting AAV-Cre into Lepr^flox/flox mice. LepR deletion in the VTA increased the dopamine levels in the NAc and enhanced the cocaine-conditioned reward. LepR deletion in the NAc core enhanced the cocaine-conditioned reward and impaired the effect of the D2-dopamine receptor on cocaine-CPP, whereas LepR deletion in the CeA had no effect on cocaine-CPP but increased the anxiety level of mice. In addition, prior exposure to saccharin increased LepR mRNA and STAT3 phosphorylation in the NAc and VTA and impaired cocaine-CPP. These results indicate that leptin signaling is critically involved in cocaine-conditioned reward and the regulation of drug reward by a natural reward and that these effects are dependent on mesolimbic LepR.