Tahon K, Wijnants M, De Schutter E, Maex R. Current source density correlates of cerebellar Golgi and Purkinje cell responses to tactile input. J Neurophysiol 105: 1327-1341, 2011. First published January 12, 2011 doi:10.1152/jn.00317.2010The overall circuitry of the cerebellar cortex has been known for over a century, but the function of many synaptic connections remains poorly characterized in vivo. We used a one-dimensional multielectrode probe to estimate the current source density (CSD) of Crus IIa in response to perioral tactile stimuli in anesthetized rats and to correlate current sinks and sources to changes in the spike rate of corecorded Golgi and Purkinje cells. The punctate stimuli evoked two distinct early waves of excitation (at Ͻ10 and ϳ20 ms) associated with current sinks in the granular layer. The second wave was putatively of corticopontine origin, and its associated sink was located higher in the granular layer than the first trigeminal sink. The distinctive patterns of granular-layer sinks correlated with the spike responses of corecorded Golgi cells. In general, Golgi cell spike responses could be linearly reconstructed from the CSD profile. A dip in simple-spike activity of coregistered Purkinje cells correlated with a current source deep in the molecular layer, probably generated by basket cell synapses, interspersed between sparse early sinks presumably generated by synapses from granule cells. The late (Ͼ30 ms) enhancement of simple-spike activity in Purkinje cells was characterized by the absence of simultaneous sinks in the granular layer and by the suppression of corecorded Golgi cell activity, pointing at inhibition of Golgi cells by Purkinje axon collaterals as a likely mechanism of late Purkinje cell excitation. in vivo electrophysiology; local field potential; microcircuit; multielectrode recording; synaptic current FOR A LONG TIME, THE CEREBELLUM has been considered to be primarily, if not exclusively, a motor organ as lesions cause symptoms such as ataxia, dysmetria, tremor, and hypotonia (Holmes 1939). Research of the past decades revealed more of its true nature: a neural substrate processing massive sensory information and serving not only motor, but also nonmotor regions

Golgi cells (GoCs) are the primary inhibitory interneurons of the granular layer of the cerebellum. Their inhibition of granule cells is central to operate the relay of excitatory inputs to the cerebellar cortex. Parallel fibers (PFs) establish synapses to the GoCs in the molecular layer; these synapses contain AMPA, N-methyl-D-aspartate (NMDA), and mostly group II metabotropic glutamate receptors. Long-term changes in the efficacy of synaptic transmission at the PF-GoC synapse have not been described previously. We used whole cell patch-clamp recordings of GoCs in acute rat cerebellar slices to study synaptic plasticity. We report that high-frequency burst stimulation of PFs, using a current-clamp or voltage-clamp induction protocol, gave rise to long-term depression (LTD) at the PF-GoC synapse. This form of LTD was not associated with persistent changes of paired-pulse ratio, suggesting a postsynaptic origin. Furthermore, LTD induction was not dependent on activation of NMDA receptors. PF-GoC LTD does require activation of specifically group II metabotropic glutamate receptors and of protein kinase A.

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