Serotonin 1A receptors play a key role in eating and sleeping. Their combined action explains why we get sleepy after a good meal. But what is the circuitry of this system? To analyze that in birds, scientists from Brazil and Germany (Bochum and Düsseldorf) joint forces and revealed the distribution of 5-HT1A receptors in the hypothalamus and brainstem of birds and analyzed their potential roles in sleep and feeding. 5-HT1A receptors are concentrated in brainstem areas like periventricular hypothalamus, preoptic nuclei and circumventricular organs that receive dense serotonergic projections. Delivering of ventricular serotonin produced a complex pattern of neuronal activations in the 5-HT1A receptor-enriched preoptic hypothalamus and the circumventricular organs, which are related to drinking and sleep regulation, but only modestly affected the activity of serotonergic neurons themselves. The same procedure induced feeding and sleeping. Further detailed experiments revealed that serotonin induces feeding and sleeping by presynaptic binding to 5-HT1A receptors that are localized in periventricular diencephalic circuits.

dos Santos, T. S., Krüger, J., Melleu, F. F., Herold, C., Zilles, K., Poli, A., Güntürkün, O., Marino-Neto, J., Distribution of serotonin 5-HT1A-binding sites in the brainstem and the hypothalamus, and their roles in 5-HT-induced sleep and ingestive behaviors in rock pigeons (Columba livia), Behav. Brain Res. 2015, 295: 45-63.