Anorexigenic effect of serotonin is associated with changes in hypothalamic nuclei activity in an avian model

The anorexigenic effect of serotonin (5HT) has been documented for decades; however, its central mechanism has not been fully elucidated, especially so in non-mammalian vertebrates. Therefore, we centrally injected 5HT to chicks and measured several appetite-associated parameters. Chicks that received central 5HT dose- and time-dependently decreased food intake while water intake was not affected. To determine which hypothalamic nuclei were associated with this effect c-Fos immunoreactivity was measured in appetite-associated nuclei. Only the ventromedial hypothalamus and arcuate nucleus were activated. Whole blood glucose was measured after 5HT injection but was not affected. From the hypothalamus, several appetite-associated mRNAs were measured by real-time PCR after 5HT injection but not one of these showed any difference in expression. Lastly, a comprehensive behavior analysis demonstrated that 5HT caused reducing pecking and increased deep rest. Together we interpret these results as exogenous 5HT injection causes short term satiety that is likely a secondary effect to an increase in the amount of time spent in deep rest.