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GABAA receptor activation suppresses Period 1 mRNA and Period 2 mRNA in the suprachiasmatic nucleus during the mid-subjective day

Authors

  • J. Christopher Ehlen,

    1. Department of Biology, Georgia State University, PO Box 4010, Atlanta, GA, 30302, USA
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  • Colleen M. Novak,

    1. Mayo Clinic, Endocrine Research Unit, St. Marys Hospital, 200 1st St. SW Joseph 5–194, Rochester, MN55905, USA
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  • Mary C. Karom,

    1. Department of Biology, Georgia State University, PO Box 4010, Atlanta, GA, 30302, USA
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  • Karen L. Gamble,

    1. Vanderbilt University, Department of Biological Sciences, 1210 MRBIII, VU Station B, Box 35–1634, Nashville, TN 37235–1634, USA
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  • Ketema N. Paul,

    1. Department of Anatomy and Neurobiology, Morehouse School of Medicine, 720 Westview Dr., Atlanta, GA, 30310, USA
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  • H. Elliott Albers

    1. Department of Biology, Georgia State University, PO Box 4010, Atlanta, GA, 30302, USA
    2. Psychology, Georgia State University, PO Box 4010, Atlanta, GA, 30302, USA
    3. Center for Behavioural Neuroscience, Georgia State University, PO Box 4010, Atlanta, GA, 30302, USA
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Dr J. Christopher Ehlen, as above.
E-mail: biocje@langate.gsu.edu

Abstract

The mammalian circadian clock can be entrained by photic and nonphotic environmental time cues. γ-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 GABAA 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 GABAA receptor activation.Together, these data indicate that, like other nonphotic stimuli, GABA suppresses Period 1- and Period 2 mRNA in the SCN.

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