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. Strain differences were observed in the factors of sleep and arousal. Melatonin contents in several brain regions including the pineal grand are higher in broiler than in layer chicks during the dark period. On the other hand, orexin-A increased arousal in layer, but not in brolier chicks. In sum, various exogenously-administrated neuropeptides and neurotransmitters cause excitation and sedation and are controlled by complex interactions in chicks. Understanding these systems may contribute to the elucidation of various physiological pathways, including those related to appetite, consciousness, and motivation.
|Title of host publication
|Hormones and Behavior
|Nova Science Publishers, Inc.
|Number of pages
|Published - Apr 1 2013
All Science Journal Classification (ASJC) codes
- Endocrine and Autonomic Systems
- Behavioral Neuroscience