Seasonal Encoding by the Circadian Pacemaker of the SCN

Feb 27, 2007Current biology : CB

How the brain's daily clock system records seasonal changes

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Abstract

Electrophysiological recordings show that the suprachiasmatic nucleus (SCN) encodes day length through varying activity profiles in mice.

Mice housed under long photoperiods (LD 16:8) exhibited broad activity profiles, while those under short photoperiods (LD 8:16) showed compressed profiles.
These activity patterns remained consistent even after mice were placed in constant darkness.
In vitro recordings confirmed that SCN electrical activity patterns differed between long and short days.
The width of multiunit activity (MUA) profiles was influenced by the phase distribution of contributing neurons within the SCN.
A significantly broader distribution of neuron phases was observed in long days compared to short days.
Long-term recordings indicated that elevated activity durations were similar in both short (3.48 hours) and long days (3.85 hours).

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The circadian pacemaker of the suprachiasmatic nucleus (SCN) functions as a seasonal clock through its ability to encode day length [1-6]. To investigate the mechanism by which SCN neurons code for day length, we housed mice under long (LD 16:8) and short (LD 8:16) photoperiods. Electrophysiological recordings of multiunit activity (MUA) in the SCN of freely moving mice revealed broad activity profiles in long days and compressed activity profiles in short days. The patterns remained consistent after release of the mice in constant darkness. Recordings of MUA in acutely prepared hypothalamic slices showed similar differences between the SCN electrical activity patterns in vitro in long and short days. In vitro recordings of neuronal subpopulations revealed that the width of the MUA activity profiles was determined by the distribution of phases of contributing units within the SCN. The subpopulation patterns displayed a significantly broader distribution in long days than in short days. Long-term recordings of single-unit activity revealed short durations of elevated activity in both short and long days (3.48 and 3.85 hr, respectively). The data indicate that coding for day length involves plasticity within SCN neuronal networks in which the phase distribution of oscillating neurons carries information on the photoperiod's duration.

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Seasonal Encoding by the Circadian Pacemaker of the SCN

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