title: GABAA receptor activation suppresses Period 1 mRNA and Period 2 mRNA in the suprachiasmatic nucleus during the mid-subjective day.
abstract: The mammalian circadian clock can be entrained by photic and nonphotic environmental time cues. gamma-aminobutyric acid (GABA) is a nonphotic stimulus that induces phase advances in the circadian clock during the middle of the subjective day. Several nonphotic stimuli suppress Period 1- and Period 2 mRNA expression in the suprachiasmatic nucleus (SCN); however, the effect of GABA on Period mRNA is unknown. In the present study we demonstrate that microinjection of the GABA(A) receptor agonist muscimol into the SCN region suppresses the expression of Period 1 mRNA in the hamster. A significant suppression of Period 2 mRNA following microinjection of muscimol was not observed in free-running conditions. However, Period 2 mRNA was significantly reduced following muscimol treatment when animals were maintained under a light cycle and transferred to constant darkness 42 h prior to treatment. An additional study investigated the maximum behavioural phase advance inducible by GABA(A) receptor activation.Together, these data indicate that, like other nonphotic stimuli, GABA suppresses Period 1- and Period 2 mRNA in the SCN.
authors.affiliation: Department of Biology, Georgia State University, Atlanta, GA, 30302, USA. biocje@langate.gsu.edu
authors.forename: J Christopher
authors.initials: JC
authors.lastname: Ehlen
authors.forename: Colleen M
authors.initials: CM
authors.lastname: Novak
authors.forename: Mary C
authors.initials: MC
authors.lastname: Karom
authors.forename: Karen L
authors.initials: KL
authors.lastname: Gamble
authors.forename: Ketema N
authors.initials: KN
authors.lastname: Paul
authors.forename: H Elliott
authors.initials: HE
authors.lastname: Albers
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D001683:Biological Clocks / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology; D006224:Cricetinae; D005136:Eye Proteins / Q000235:genetics* / Q000378:metabolism; D018755:GABA Agonists / Q000008:administration & dosage / Q000378:metabolism; D017403:In Situ Hybridization; D008297:Male; D008647:Mesocricetus; D008845:Microinjections; D009118:Muscimol / Q000008:administration & dosage / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D056950:Period Circadian Proteins; D017440:Photoperiod; D012333:RNA, Messenger / Q000378:metabolism*; D011963:Receptors, GABA-A / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D005136:Eye Proteins; D018755:GABA Agonists; D009687:Nuclear Proteins; D056950:Period Circadian Proteins; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D014157:Transcription Factors; D009118:Muscimol