Electrical synapses coordinate activity in the suprachiasmatic nucleus

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Abstract

In the suprachiasmatic nucleus (SCN), the master circadian pacemaker, neurons show circadian variations in firing frequency. There is also considerable synchrony of spiking across SCN neurons on a scale of milliseconds, but the mechanisms are poorly understood. Using paired whole-cell recordings, we have found that many neurons in the rat SCN communicate via electrical synapses. Spontaneous spiking was often synchronized in pairs of electrically coupled neurons, and the degree of this synchrony could be predicted from the magnitude of coupling. In wild-type mice, as in rats, the SCN contained electrical synapses, but electrical synapses were absent in connexin36-knockout mice. The knockout mice also showed dampened circadian activity rhythms and a delayed onset of activity during transition to constant darkness. We suggest that electrical synapses in the SCN help to synchronize its spiking activity, and that such synchrony is necessary for normal circadian behavior.

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Figure 1: Electrical coupling in the SCN.
Figure 2: Electrical synapses synchronize spiking between SCN pairs.
Figure 3: Electrophysiology and circadian behavior in wild-type (WT) and Cx36-knockout (KO) mice.
Figure 4: Means of circadian measures of locomotor activity across blocks of 10 d for the four wild-type (WT) and four Cx36-knockout (KO) mice that were maintained in constant darkness (DD) for the full 50 d.

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Acknowledgements

We thank S. Patrick for technical help, A. Jackson, M. Carskadon and D. Berson for comments on the manuscript, and M. Deans and D. Paul for the Cx36-knockout mouse line. This research was supported by a Sidney A. Fox and Dorothea Doctors Fox Postdoctoral Fellowship to M.A.L. and by US National Institutes of Health grants MH60284 to R.D.B. and NS25983 and DA12500 to B.W.C.

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Correspondence to Barry W Connors.

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Long, M., Jutras, M., Connors, B. et al. Electrical synapses coordinate activity in the suprachiasmatic nucleus. Nat Neurosci 8, 61–66 (2005) doi:10.1038/nn1361

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