LEP and obesity due to melanocortin 4 receptor deficiency: - Compared with those fed the LFD, mice fed the HFD weighed 24% more after 15 weeks.- The HFD was associated with higher leptin levels.- After 15 weeks, the same dose of intraperitoneal leptin that was effective in mice fed the LFD was unable to induce STAT3 DNA binding activity in hypothalamus of mice of Group 1, indicating leptin resistance.- Similar doses of intracerebroventricular induced STAT3 activation in mice with 15 weeks of diet-induced obesity, which suggests a failure to deliver leptin to areas of action in the hypothalamus.