Neuroendocrine Regulation of Sedation and Excitation in Neonatal Chicks (pp. 1-28)
Authors: (Mitsuhiro Furuse, Mark A. Cline, Takashi Bungo, Kunio Sugahara, Laboratory of Regulation in Metabolism and Behavior, Faculty of Agriculture, Kyushu University, Fukuoka, Japan, and others)
Abstract: The neuroendocrine system regulates arousal, and exogenous intracerebroventricular (i.c.v.) injection of some neuropeptides and neurotransmitters in chicks can cause excitation (moving more and vocalizing loudly), while others induce a sedation state (being calm and moving less with or without hypnosis). One such excitatory neuropeptide is corticotropin-releasing factor (CRF), which when i.c.v. injected stimulates the hypothalamic-pituitary-adrenal (HPA) axis and induces excitation. However, this response is dependent on stock: plasma corticosterone concentrations are higher in layer-type (layer) than in meat-type (broiler) chicks. In contrast, glucagon-like peptide-1 (GLP-1) induces sedation with hypnosis partly through activation of adrenergic pathways, a response that is also stock dependent: broiler chicks sleep more than layer chicks.
Endogenous neurotransmitter systems do not function independently: co-injection of CRF and GLP-1 caused intermediate behaviors, implying that the two peptides interact in the chick brain. In addition to GLP-1, norepinephrine and serotonin also interact with CRF, but through different mechanisms, to attenuate CRF-induced behavior. Additionally, melatonin attenuated the stimulation of HPA axis by CRF.