title: Activation of growth hormone secretagogue receptor induces time-dependent clock phase delay in mice.
abstract: Early studies have reported a phase-shifting effect of growth hormone secretagogues (GHSs). This study aimed to determine the mechanism of action of GHSs. We examined the response of the hypothalamic suprachiasmatic nuclei (SCN) to growth hormone releasing peptide-6 (GHRP-6) by assessing effects on the phase of locomotor activity rhythms, SCN neuronal discharges, and the potential signaling pathways involved in the drug action on circadian rhythms. The results showed that bolus administration of GHRP-6 (100 μg/kg ip) at the beginning of subjective night (CT12) induced a phase delay of the free-running rhythms in male C57BL/6J mice under constant darkness, but did not elicit phase shift at other checked circadian time (CT) points. The phase-delay effect of GHRP-6 was abolished by d-(+)-Lys-GHRP-6 (GHS receptor antagonist), KN-93 [calcium/calmodulin-dependent protein kinase II (CaMK) II inhibitor], or anti-phosphorylated (p)-cAMP response element-binding protein (CREB) antibody. Further analyses demonstrated that GHRP-6 at CT12 induced higher calcium mobilization and neuronal discharge in the SCN compared with that at CT6, decreased the levels of glutamate and γ-aminobutyric acid, increased the levels of p-CaMKII, p-CREB, and period 1, and delayed the circadian expressions of circadian locomotor output cycles kaput, Bmal1, and prokineticin 2 in the SCN; these signaling changes resulted in behavioral phase delay. Collectively, GHRP-6 induces a CT-dependent phase delay via activating GHS receptor and the downstream signaling, which is partially similar to the signaling cascade of light-induced phase delay at early night. These novel observations may help to better understand the role of GHSs in circadian physiology.
authors: Department of Physiology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China.
authors: Lan
authors: L
authors: Zhou
authors: Department of Physiology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China.
authors: Qian
authors: Q
authors: Gao
authors: Department of Physiology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China.
authors: Peng
authors: P
authors: Zhang
authors: Department of Physiology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China.
authors: Shu
authors: S
authors: Guo
authors: Department of Physiology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China.
authors: Jingli
authors: J
authors: Gu
authors: Department of Physiology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China.
authors: Wei
authors: W
authors: Hao
authors: Department of Physiology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, School of Basic Medicine, Peking Union Medical College, Beijing, China caojimin@126.com.
authors: Ji-Min
authors: JM
authors: Cao
mesh_terms: D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002940:Circadian Rhythm / Q000187:drug effects*; D056925:Circadian Rhythm Signaling Peptides and Proteins / Q000378:metabolism; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D003627:Data Interpretation, Statistical; D005434:Flow Cytometry; D018698:Glutamic Acid / Q000378:metabolism; D007150:Immunohistochemistry; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000187:drug effects; D056950:Period Circadian Proteins / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D054440:Receptors, Ghrelin / Q000819:agonists*; D013493:Suprachiasmatic Nucleus / Q000187:drug effects / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D056925:Circadian Rhythm Signaling Peptides and Proteins; D017362:Cyclic AMP Response Element-Binding Protein; C539023:Per1 protein, mouse; D056950:Period Circadian Proteins; D054440:Receptors, Ghrelin; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2
keywords: growth hormone releasing peptide-6; growth substances; nonphotic cues; phase shift; prokineticins