SUBMILLISECOND KINETICS AND LOW EFFICACY OF PARALLEL FIBER GOLGI CELLSYNAPTIC CURRENTS IN THE RAT CEREBELLUM

1. The whole-cell configuration of the patch clamp technique was used to record from Golgi cells in thin slices of the rat cerebellum (P12-P 25). Their active membrane properties and the input that they receive from the parallel fibres were characterized. 2. Most cells were filled with biocytin and morphologically identified by the presence of a lar ge axonal arbor restricted to the granular layer. The morphological pa rameters of eighteen of the best-preserved cells were quantified. 3. A slow capacitive current transient, characteristic of the Golgi cell a xon, was used to identify Golgi cells whenever their morphology could not be preserved. 4. Golgi cells fire action potentials spontaneously at 3 +/- 1.7 Hz (n = 17). Their firing frequency increases linearly wi th the amplitude of depolarizing current pulses and displays marked ad aptation. 5. When hyperpolarized Golgi cells display an anomalous rect ification which is blocked by 2 mM CsCl, indicating the presence of an I-h-like current. 6. Golgi cells receive a spontaneous excitatory inp ut from parallel fibres. This input is composed of small amplitude, mo stly monoquantal, EPSCs. Chemical stimulation of granule cells by loca lly applied kainate evokes tetrodotoxin (TTX)-dependent events with si milar properties. 7. The parallel fibre-Golgi cell EPSCs have both AMP A and NMDA components. The NMDA component is blocked by 1 mM external magnesium at -60 mV and decays with time constants of 31 +/- 9 ms and 170 +/- 15 ms (at +61 mV in the presence of magnesium). 8. In the pres ence of 10 mu M internal spermine, the AMPA component of the spontaneo us EPSCs is markedly slowed (0.96 +/- 0.25 ms to 1.86 +/- 0.47 ms; n = 4) and reduced in amplitude (49 +/- 7%; n = 4) when depolarizing the cell from -70 mV to +61 mV. 9. The decay kinetics of individual AMPA E PSCs were found to be variable, in part because of dendritic filtering . ii more detailed analysis reveals that the synaptic AMPA conductance s are regulated during development and close faster at days P19-P25 th an at days P13-P16. 10. These data suggest that the efficacy of the pa rallel fibre-Golgi cell input is rather low. This places strong constr aints on the conditions in which the inhibitory feedback exerted by th e Golgi cell can be operational. 11. The possibility is considered tha t the Golgi cell-granule cell circuit shows an oscillatory behaviour. This hypothesis is discussed in relation to the models of Albus and Ma rr.