Cerebellar Golgi cells in the rat: receptive fields and timing of responses to facial stimulation.

Golgi cells are the only elements within the cerebellar cortex that inhibit granule cells. Despite their unique position there is little information on how Golgi cells respond to afferent input. We studied responses of Golgi cells to mechanical stimulation of the face, in Crus I-II of ketamine-xylazine anaesthetized rats. In 41 rats, 87 putative Golgi cells were identified, based on spike characteristics and on location of electrolytic lesions in the granular layer. They displayed a slow firing rhythm at rest (8.4 spikes/s). Most Golgi cells (84%) showed excitatory responses to tactile input. Their receptive fields (RFs) included, in 78%, the entire ipsilateral infraorbital nerve territory, and extended, in 14%, to other trigeminal nerve branches and, in 48%, to the contralateral face. Excitatory responses consisted of multiple, precisely timed (+/- 1 ms) spikes. Most peristimulus time histograms (PSTHs) (69%) showed an early (5-10 ms) and a late (13-26 ms) excitatory component, with each component consisting of a single PSTH peak. In some PSTHs the early component was a double peak (< 4 ms interval). In others, only one, early or late, PSTH peak was observed. The excitatory components were followed by a silent period (28-69 ms latency), the duration of which (13-200 ms) varied with response amplitude. In single cells, response profiles changed with stimulus location. In simultaneously recorded cells, evoked profiles differed for identical stimuli. Differences in RF size between early 'double' and 'single' peaks suggested that they resulted from direct mossy fibre and parallel fibre input, respectively. Late PSTH peaks were assumed to reflect corticopontine activation.