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Developmental Biology - Circadian Clock
GABA Influences Circadian Clock Signals
The GABA enzyme affects day to night oscillations from our circadian clock...
Behaviors such as sleeping/waking, body temperature and endocrine function, operate through 24-hour oscillations called circadian rhythms.
Research led by the Graduate Schools of Medicine at Nagoya University, Japan, collaborating with Hokkaido University and Gunma University Graduate School of Medicine, Japan, reveals how neurons in the mammalian brain work together refining the rhythmic signals all mammalian brains exude from their internal circadian clock.
Physiology and behavior are regulated by the centrally located SCN or Suprachiasmatic Nucleus, and these recent findings help us understand how the SCN continually regulates itself. The findings might aid in the development of new clinical approaches for a variety of diseases related to mistimed circadian rhythms. The observations were published online in the journal Communications Biology.
Research Background
SCN oscillations dictate day to night alternations in nerve signalling.
The SCN is made up of diverse neurons with various neurotransmitters. One inhibitory neurotransmitter, Y-Amino-Butyric-Acid (or GABA) functions in almost every SCN neuron.
Research Results
In the present study, researchers examined GABA signaling within the SCN of mouse brains that do not have vesicular GABA (VGAT) transporter or the GABA synthesizing enzyme, glutamate decarboxylase. VGAT is a signal transporter thought to mediate the accumulation of GABA.
Simultaneously, researchers measured circadian rhythms using a bioluminescence signal reporter looking for the clock gene PER2 in order to measure spontaneous signal firing and increases in intracellular calcium (Ca2+) levels. All tests were done over several circadian cycles, and conducted on cultured SCN slices of perinatal mice.
Researchers found that SCN slices without GABA exhibited bursts of signal firing throughout a 24hour day. These SCN firing bursts were associated with an abrupt increase in intracellular Ca2+, synchronous throughout an entire SCN brain slice.
In contrast, the circadian PER2 rhythm was kept essentially intact, as researchers found SCN-specific VGAT depletion deteriorated circadian behavioral rhythms.
Summary
GABA appears needed to suppress burst firing in fetal SCN neurons along with mediating abrupt calcium (Ca2+) spikes. It may be that it refines circadian firing rhythms to ensure noiseless communication with neurons outside the SCN.
Abstract
In mammals, circadian rhythms are regulated by a central clock — located in the hypothalamic suprachiasmatic nucleus (SCN). It's composed of heterogeneous (or non-uniform) neurons with various neurotransmitters. Among them an inhibitory neurotransmitter, Y-Amino-Butyric-Acid (GABA), is expressed in almost all SCN neurons, however, its role in the circadian physiology is still unclear. Here, we show that the SCN of fetal mice lacking vesicular GABA transporter (VGAT-/-) or GABA synthesizing enzyme, glutamate decarboxylase (GAD65-/-/67-/-), shows burst firings associated with large Ca2+ spikes throughout 24 hours, which spread over the entire SCN slice in synchrony. By contrast, circadian PER2 rhythms in VGAT-/- and GAD65-/-/67-/- SCN remain intact. SCN-specific VGAT deletion in adult mice dampens circadian behavior rhythm. These findings indicate that GABA in the fetal SCN is necessary for refinement of the circadian firing rhythm and, possibly, for stabilizing output signals, but not for circadian integration of multiple cellular oscillations.
Authors
Daisuke Ono, Ken-ichi Honma, Yuchio Yanagawa, Akihiro Yamanaka and Sato Honma.
Acknowledgements
The authors thank J.S. Takahashi for providing PER2::LUC mice, S. Kuroda and T. Ueda for the analysis program of time-laps images, M. Mieda for advice on AAV purification, and R. Enoki on technical advice for fluorescence imaging. The authors thank Genetically-Encoded Neuronal Indicator and Effector (GENIE) Project and the Janelia Farm Research Campus of the Howard Hughes Medical Institute for sharing GCaMP6s constructs. This work was supported in part by The Uehara Memorial Foundation, The Nakajima Foundation, GSK Japan Research Grant 2015, Kowa Life Science Foundation, Takeda Science Foundation, Kato Memorial Bioscience Foundation, the Project for Developing Innovation Systems of the MEXT, and Creation of Innovation Centers for Advanced Interdisciplinary Research Areas Program, Ministry of Education, Culture, Sports, Science and Technology, Japan and JSPS KAKENHI (Nos. 15H04679, 26860156, 15K12763, 26290002, 15H05872, 17H05550, and 18H02477).
This work was supported in part by The Uehara Memorial Foundation, The Nakajima Foundation, GSK Japan Research Grant 2015, Kowa Life Science Foundation, Takeda Science Foundation, Kato Memorial Bioscience Foundation, the Project for Developing Innovation Systems of the MEXT, and Creation of Innovation Centers for Advanced Interdisciplinary Research Areas Program, Ministry of Education, Culture, Sports, Science and Technology, Japan and JSPS KAKENHI (No. 15H04679, No. 26860156, No. 15K12763, No. 26290002, No. 15H05872, No. 17H05550, No. 18H02477).
The authors declare no competing interests.
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Sep 9 2019 Fetal Timeline Maternal Timeline News
 AAV (adeno-associated virus) mediated VGAT(vesicular GABA) deficiency in the hypothalamic suprachiasmatic nucleus (SCN) deteriorates circadian rhythms. CREDIT Nagoya University.
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