Synaptic‐ and agonist‐induced excitatory currents of Purkinje cells in rat cerebellar slices.

Abstract

1. Postsynaptic currents originating from activation of the two major excitatory inputs to Purkinje cells were studied in thin slices of rat cerebellum, using the tight‐seal whole‐cell recording technique. Two types of excitatory postsynaptic currents were analysed: those evoked by stimulation of the granule cell‐parallel fibre system (PF‐EPSC) and those elicited by stimulation of the climbing fibres (CF‐EPSC). 2. Both types of postsynaptic currents had a linear current‐voltage relation, reversing at membrane potentials close to 0 mV. Their time course of activation was independent of the membrane potential. 3. For both types of postsynaptic currents, the time course of decay was well described by a single exponential function, with a time constant which increased as the membrane potential was made more positive. 4. Postsynaptic currents arising from stimulation of the climbing fibre generally had a slightly faster time course of onset and decay than those associated with stimulation of the granule cell‐parallel fibre system. The average values of the 10‐90% rise time were 1.8 +/‐ 0.4 ms (means +/‐ S.D., n = 7) for PF‐EPSCs and 0.8 +/‐ 0.3 ms (n = 9) for CF‐EPSCs. Time constants of decay, at a holding potential of ‐60 mV, had values of 8.3 +/‐ 1.6 ms (n = 7) and 6.4 +/‐ 1.1 ms (n = 9) for PF‐EPSCs and CF‐EPSCs respectively. 5. CF‐EPSCs and PF‐EPSCs had the characteristics described above in slices derived from animals aged 9‐22 days old and 9‐15 days old, respectively. The PF‐EPSCs in animals older than 15 days had very slow time courses and positive apparent reversal potentials, suggesting that they originated from distal locations, not under accurate voltage control. 6. In order to assess the quality of the voltage clamp, responses to hyperpolarizing pulses from ‐70 mV were analysed. The capacitive currents could be fitted by the sum of two exponentials, and were interpreted with an equivalent electrical circuit comprising two main compartments (soma and proximal dendrites on one hand, distal dendrites on the other). Analysis of synaptic currents in terms of this model suggested that the recorded time course of decay was approximately correct. 7. CF‐EPSCs as well as PF‐EPSCs were insensitive to the NMDA receptor antagonist 3‐3(2‐carboxypiperazine‐4‐yl)propyl‐1‐phosphonate (CPP), but were blocked in a dose‐dependent reversible manner by the non‐NMDA antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX).(ABSTRACT TRUNCATED AT 400 WORDS)