Golgi cells are an important element of the cerebellar cortical circuitry. They inhibit granule cells, which are the only excitatory cells in the cerebellar cortex, and are thus in a position to mediate transmission into the cortex through the mossy fibre pathway. Previous work has shown that these neurones respond to activation of an excitatory peripheral receptive field with brief accelerations of their spike activity (e.g. Vos et al. 2000). In this study we describe a different response to peripheral inputs.

The experiments were performed in seven rats under general anaesthesia (urethane 1000 mg kg^-1 I.P., supplemented if required). At the end of the experiments the animals were killed with an overdose of the anaesthetic. Using a multiple microelectrode device we were able to record from up to seven Golgi cells simultaneously within a small (1 mm²) area of cortex over crus II. Brief electrical stimuli delivered through percutaneous pins were used to activate peripheral afferents. We characterised the responses of Golgi cells into three stereotypical types: short latency excitations (as described previously), short latency depressions of firing and long latency depressions of firing. The latter was the most common response we encountered (69 % of cells tested). Furthermore this response was frequently evoked from multiple peripheral sites (bilaterally, from fore- and hindlimbs and face). From studies in which we directly stimulated isolated peripheral nerves we were able to evoke these responses with weak stimuli (< 2 T). Thus large myelinated mechanoreceptive afferents are likely to contribute to them.

The nature of these responses is puzzling: there are few known candidates that could mediate postsynaptic inhibition of Golgi cells. Purkinje cell collaterals are one possibility, but Purkinje cells local to the Golgi cells we recorded seldom responded to the stimuli we used, so local collaterals were unlikely to have mediated these effects. The depression in firing rate was often sustained and substantial, suggesting that it would be accompanied by a powerful effect on granule cells. The widespread nature of the long latency depressions in Golgi cell firing suggest that they are evoked through a pathway with widespread convergence. The identity of this pathway is currently under investigation.