title: Gastrin-releasing peptide phase-shifts suprachiasmatic nuclei neuronal rhythms in vitro.
abstract: The main mammalian circadian pacemaker is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Gastrin-releasing peptide (GRP) and its receptor (BB(2)) are synthesized by rodent SCN neurons, but the role of GRP in circadian rhythm processes is unknown. In this study, we examined the phase-resetting actions of GRP on the electrical activity rhythms of hamster and rat SCN neurons in vitro. In both rat and hamster SCN slices, GRP treatment during the day did not alter the time of peak SCN firing. In contrast, GRP application early in the subjective night phase-delayed, whereas similar treatment later in the subjective night phase-advanced the firing rate rhythm in rat and hamster SCN slices. These phase shifts were completely blocked by the selective BB(2) receptor antagonist, [d-Phe(6), Des-Met(14)]-bombesin 6-14 ethylamide. We also investigated the temporal changes in the expression of genes for the BB(1) and BB(2) receptors in the rat SCN using a quantitative competitive RT-PCR protocol. The expression of the genes for both receptors was easily detected, but their expression did not vary over the diurnal cycle. These data show that GRP phase-dependently phase resets the rodent SCN circadian pacemaker in vitro apparently via the BB(2) receptor. Because this pattern of phase shifting resembles that of light on rodent behavioral rhythms, these results support the contention that GRP participates in the photic entrainment of the rodent SCN circadian pacemaker.
authors.affiliation: Biomedical Sciences, King's College London, London, United Kingdom SE1 1UL.
authors.forename: A J
authors.initials: AJ
authors.lastname: McArthur
authors.forename: A N
authors.initials: AN
authors.lastname: Coogan
authors.forename: S
authors.initials: S
authors.lastname: Ajpru
authors.forename: D
authors.initials: D
authors.lastname: Sugden
authors.forename: S M
authors.initials: SM
authors.lastname: Biello
authors.forename: H D
authors.initials: HD
authors.lastname: Piggins
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects; D001839:Bombesin / Q000031:analogs & derivatives* / Q000494:pharmacology; D002940:Circadian Rhythm / Q000187:drug effects / Q000502:physiology*; D006224:Cricetinae; D003624:Darkness; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D019886:Gastrin-Releasing Peptide / Q000008:administration & dosage / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008647:Mesocricetus; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D017440:Photoperiod; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017208:Rats, Wistar; D018004:Receptors, Bombesin / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D012333:RNA, Messenger; D018004:Receptors, Bombesin; C086327:bombesin (6-14)-ethylamide, Phe(6)-des-Met(14)-; D019886:Gastrin-Releasing Peptide; D001839:Bombesin