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J Neurophysiol 85: 323-331, 2001;
0022-3077/01 $5.00
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The Journal of Neurophysiology Vol. 85 No. 1 January 2001, pp. 323-331
Copyright ©2001 by the American Physiological Society

Postsynaptic Currents in Deep Cerebellar Nuclei

Davide Anchisi,1 Bibiana Scelfo,1 and Filippo Tempia1,2

 1Department of Neuroscience, University of Turin, I-10125 Turin; and  2Department of Internal Medicine, Section of Human Physiology, University of Perugia, I-06126 Perugia, Italy

Anchisi, Davide, Bibiana Scelfo, and Filippo Tempia. Postsynaptic Currents in Deep Cerebellar Nuclei. J. Neurophysiol. 85: 323-331, 2001. Postsynaptic currents were studied by whole cell recordings in visually identified large neurons of the deep cerebellar nuclei (DCN) in slices of 4- to 11-day-old mice. Spontaneous postsynaptic currents were abolished by the GABAA receptor antagonist bicuculline and had a single-exponential decay with a mean time constant of 13.6 ± 3.2 (SD) ms. Excitatory postsynaptic currents (EPSCs) were evoked in 48/56 neurons recorded. The addition of AMPA and N-methyl-D-aspartate (NMDA) receptor antagonists together completely abolished all synaptic responses. In 1 mM [Mg2+]o and at a holding potential of -60 mV, the peak amplitude of the NMDA component of the EPSC (NMDA-EPSC) was 83.2 ± 21.2% of the AMPA component (AMPA-EPSC). This indicates that in DCN neurons, at a physiological [Mg2+]o and at the resting membrane potential, NMDA receptors contribute to the synaptic signal. AMPA-EPSCs had a linear current-voltage relationship with a reversal potential of +2.3 ± 0.4 mV and a single-exponential decay with a voltage-dependent time constant that at -60 mV was 7.1 ± 3.3 ms. In 10 µM glycine and 1 mM [Mg2+]o, the I-V relationship of NMDA-EPSCs had a reversal potential of -0.5 ± 3.3 mV and a maximal inward current at -33.4 ± 5.8 mV. The apparent dissociation constant (KD) of Mg2+ for the NMDA receptor-channel at -60 mV, measured by varying [Mg2+]o, was 135.5 ± 55.3 µM, and when measured by fitting the I-V curves with a theoretical function, it was 169.9 ± 119.5 µM. Thus in the DCN, NMDA receptors have a sensitivity to Mg2+ that corresponds to subunits that are weakly blocked by this ion (epsilon 3 and epsilon 4) of which the DCN express epsilon 4. NMDA-EPSCs had a double-exponential decay with voltage-dependent time constants that at -60 mV were 20.2 ± 8.9 and 136.4 ± 62.8 ms. At positive voltages, the time constants were slower and their contributions were about equal, while in the negative slope conductance region of the I-V curve, the faster time constant became predominant, conferring faster kinetics to the EPSC. The weak sensitivity to Mg2+ of NMDA receptors, together with a relatively fast kinetics, provide DCN neurons with strong excitatory inputs in which fast dynamic signals are relatively well preserved.




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