Stimulation of cat cutaneous nociceptive C fibres causing tonic and synchronous activity in climbing fibres.

1. The input from cutaneous nociceptors to climbing fibres projecting to the forelimb area of the C3 zone in the cerebellar anterior lobe was examined in barbiturate-anaesthetized cats. Climbing fibre responses were simultaneously recorded in single Purkinje cells and as field potentials from the cerebellar surface close to these cells. 2. The cutaneous receptive field of the climbing fibres studied were located on the ipsilateral forelimb. All climbing fibres were activated by both non-noxious tactile stimulation and noxious pinch of the skin. The location of the receptive field and the distribution of sensitivity in the receptive field appeared to be identical for noxious and tactile stimuli. 3. A phasic response in the climbing fibres was evoked by either short- or long-lasting non-noxious pressure applied to their cutaneous receptive field. By contrast, all climbing fibres studied were strongly and tonically activated (up to 4-11 Hz for the duration of the stimulation) by sustained noxious pinch in the most sensitive area of their receptive fields. 4. Experiments with anodal block of impulse conduction in myelinated fibres indicated that a major input to climbing fibres during sustained noxious pinch originates from nociceptive C fibres. 5. Sustained noxious pinch of the skin evoked large field potentials on the cerebellar surface. These field potentials were evoked simultaneously with climbing fibre responses in single Purkinje cells and were due to synchronous activation of many climbing fibres. These field potentials and discharges in single climbing fibres were elicited from the same area of the skin suggesting that many of the synchronously discharging climbing fibres have the same receptive field on the skin.