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The Journal of Neuroscience, March 15, 2003, 23(6):2019
Coexistence of Excitatory and Inhibitory GABA Synapses in the
Cerebellar Interneuron Network
Joël
Chavas and
Alain
Marty
Laboratoire de Physiologie Cérébrale, Université
Paris 5, 75270 Paris, France
Functional GABA synapses are usually assumed to be inhibitory.
However, we show here that inhibitory and excitatory GABA connections coexist in the cerebellar interneuron network. The reversal potential of GABAergic currents (EGABA)
measured in interneurons is relatively depolarized and contrasts with
the hyperpolarized value found in Purkinje cells ( 58 and 85 mV
respectively). This finding is not correlated to a specific
developmental stage and is maintained in the adult animal.
EGABA in interneurons is close to the mean membrane potential (56.5 mV, as measured with a novel "equal firing
potential" method), and both parameters vary enough among cells so
that the driving force for GABA currents can be either inward or
outward. Indeed, using noninvasive cell-attached recordings, we
demonstrate inhibitory, excitatory, and sequential inhibitory and
excitatory responses to interneuron stimulation [results obtained both
in juvenile (postnatal days 12-14) and subadult (postnatal days
20-25) animals]. In hyperpolarized cells, single synaptic GABA
currents can trigger spikes or trains of spikes, and subthreshold stimulations enhance the responsiveness to subsequent excitatory stimulation over at least 30 msec. We suggest that the coexistence of
excitatory and inhibitory GABA synapses could either buffer the mean
firing rate of the interneuron network or introduce different types of
correlation between neighboring interneurons, or both.
Key words:
cerebellum; Purkinje cells; basket cells; GABA; synapses; gramicidin-perforated patch
Copyright © 2003 Society for Neuroscience 0270-6474/03/2362019-13$05.00/0
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