Mossy and climbing fiber inputs from cutaneous mechanoreceptors to cerebellar Purkynĕ cells in unanesthetized cats.

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1. Mossy and climbing fiber inputs from cutaneous mechanoreceptors to Purkynĕ cells of vermis and pars intermedia of the cerebellar anterior lobe were studied in locally anesthetized, paralyzed cats prepared for painless recording sessions. In this preparation the mossy fiber and climbing fiber pathways remain fully functional. Simple spikes and climbing fiber discharges were recorded simultaneously through extracellular glass micro-electrodes and thereafter filtered off from each other for separate, computer-assisted analysis. Controlled mechanical stimulation (air jets, taps, pressure) was performed on the foot pads of all four limbs and on the hairy skin of the limbs and the body. 2. Long term recording of the spontaneous activity of 110 Purkynĕ cells revealed a simple spike activity of 85 imp./s +/- 49 imp./s (mean +/- S.D.) and 1.00+/-0.78 climbing fiber responses per second. 3. Taps to foot pads and air jets to hairy skin revealed that most of the short latency responses via mossy fibers resulted from activation of the receptors of the ipsilateral forefoot. With the same stimuli climbing fiber discharges from the ipsilateral feet were more frequently evoked than from the contralateral feet. Both via mossy and climbing fibers the contralateral hindlimb gave the smallest contribution. 4. Simple spike responses were evoked more commonly by pad stimulation (tap stimuli) than by hair stimulation (air jets). For both types of stimuli excitatory responses were more frequent (3:1) than inhibitory ones. Similarly, pad stimulation was more effective than hair stimulation in inducing climbing fiber responses. Ipsilateral stimuli were much more effective than contralateral ones in evoking both simple spike and climbing fiber responses. 5. Steady pressure stimuli modify the Purkynĕ cell discharges via mossy and climbing fiber pathways. Excitatory and inhibitory effects often of very long duration have been observed via both pathways. Again the ipsilateral forelimb was more effective than the other limbs. Mossy fiber responses were at least three times as common as climbing fiber responses and excitatory responses were more frequent than inhibitory ones. 6. There is no apparent relation between the spontaneous discharge rates of the Purkynĕ cells and the response magnitudes of the mossy fiber and climbing fiber induced excitatory and inhibitory changes inthe impulse pattern of Purkynĕ cells during steady pressure stimuli.