Leptin depresses food intake in great tits (Parus major).

Food availability for wild organisms typically varies both in time and space, requiring a mechanism that regulates the storage of excess energy and makes it possible to use stores during energy shortfall. Leptin, a protein hormone encoded by an obesity gene, has been suggested to be the signal mediator for this flux of energy. In a controlled laboratory experiment on caged great tits (Parus major) we evaluated the effect of leptin on food intake and behaviour. Experimental birds were given an intramuscular injection of 10 microg leptin dissolved in phosphate buffered saline (PBS), while the control birds were injected with PBS only at 09:00 h after a night's fasting. Within the first 20 min after injections we observed a significant difference in food intake between groups: control birds initially fed at higher rates compared to leptin treated birds. The cumulative food intake suggested that the effect of leptin disappeared after approximately 40-50 min post-injections. Similar results have previously been found in domesticated chickens. To our knowledge, this is the first study to show that leptin depresses food intake in wild birds.