Serotonin modifies corticotropin-releasing factor-induced behaviors of chicks

Glucagon-like peptide-1 (GLP-1) decreased corticotropin-releasing factor (CRF)-induced behaviors in neonatal chicks, and serotonin is one of the possible mechanisms through which GLP-1 affects CRF-induced behaviors. The present experiments were conducted to confirm the effect of serotonin on CRF-induced behaviors. In Experiment 1, chicks were intracerebroventricularly injected with either saline, 0.1 microg of CRF, 5.0 microg of serotonin, or 0.1 microg of CRF plus 5.0 microg of serotonin. Injection of CRF caused excitation as evidenced by increased spontaneous activities and distress vocalizations (DVs) compared to the control group. The effect of CRF was attenuated by serotonin since chicks became quiet after given CRF with serotonin. Sleep-like behaviors were observed in the serotonin group. The number of defecations was increased by CRF and decreased by serotonin. Both CRF and serotonin increased plasma corticosterone, and the effect was synergistic. Serotonin dose-dependently decreased locomotor activities of chicks after central administration of 0.1 microg of CRF, 0.1 microg of CRF plus 2.5, 5.0, or 10.0 microg of serotonin in Experiment 2. CRF-induced DVs were modified by serotonin. Instead of DVs, tender and low-pitched vocalizations were observed in chicks treated with CRF plus serotonin, the voice frequencies of which were less than 10 kHz. In conclusion, serotonin attenuated the CRF-induced behaviors while stimulating corticosterone release. These results indicate that the role of serotonin is dependent on the behaviors being measured.