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The Journal of Neurophysiology Vol. 87 No. 2 February 2002, pp. 834-844
Copyright ©2002 by the American Physiological Society
Netherlands Institute for Brain Research, 1105 AZ Amsterdam ZO, The Netherlands
De Jeu, Marcel and
Cyriel Pennartz.
Circadian Modulation of GABA Function in the Rat Suprachiasmatic
Nucleus: Excitatory Effects During the Night Phase. J. Neurophysiol. 87: 834-844, 2002. Gramicidin-perforated patch-clamp recordings were made from slices of
the suprachiasmatic nucleus (SCN) of adult rats to characterize the
role of
-amino butyric acid (GABA) in the circadian timing system.
During the day, activation of GABAA receptors
hyperpolarized the membrane of SCN neurons. During the night, however,
activation of GABAA receptors either
hyperpolarized or depolarized the membrane. These night-restricted
depolarizations in a large subset of SCN neurons were capable of
triggering spikes and thus appeared to be excitatory. The
GABAA reversal potentials of SCN neurons revealed a significant day-night difference with more depolarized
GABAA reversal potentials during the night than
during the day. The emergence of depolarizing
GABAA-mediated responses in a subset of SCN
neurons at night can be ascribed to a depolarizing shift in
GABAA reversal potential. The
GABAA receptor antagonist bicuculline (12.5 µM)
increased the spontaneous firing rate of all SCN neurons during the
day, indicating that spontaneous GABAA-mediated
inputs inhibited the SCN neurons during this period. The effect of
bicuculline (12.5 µM) on the spontaneous firing rate of SCN neurons
during the night was heterogeneous due to the mixture of depolarizing and hyperpolarizing GABAA-mediated inputs during
this period. We conclude that GABA uniformly acts as an inhibitory
transmitter during the day but excites a large subset of SCN neurons at
night. This day-night modulation of GABAergic neurotransmission
provides the SCN with a time-dependent gating mechanism that may
counteract propagation of excitatory signals throughout the biological
clock at day but promotes it at night.
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