Objective: This study was designed to determine whether pinealectomy has an effect on food intake in mice. The efficiency of melatonin in restoring the possible effect of pinealectomy on food intake was also investigated. To determine whether melatonin has a modulatory role in the effect of leptin on food intake, the influence of leptin on food intake in pinealectomized animals were also examined.

Materials and methods: Adult male mice weighing 30-40 g were used in this study. The animals were divided into two main groups, each consisting 5 animals. The mice of the control group were exposed to sham-pinealectomy. In the experimental group, mice were pinealectomized and allowed to recover for a period of two weeks. Mice received daily injections of melatonin (5 mg/kg/day, i.p.) and luzindole (10 mg/kg/day, i.p.). Mice were i.p. injected with leptin in a dose of 25 μg/mouse in 0.1 mL 15 mM HCl. Control animals were injected with the respective vehicle.

Results: Pinealectomy caused a significant decrease in food intake in mice. Melatonin restored this decrease in food intake caused by pinealectomy. Luzindole, a melatonin antagonist, did not reverse melatonin-induced increase in food intake. Leptin significantly decreased food intake in pinealectomized and sham-pinealectomized animals.

Conclusion: In conclusion, melatonin was found to increase food intake physiologically and pharmacologically in mice. Further studies are needed to determine the mechanism by which melatonin exerts its effect on food intake in mice.