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

Abstract

SUMMARY1. 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.

Dendritic glutamate release produces autocrine activation of mGluR1 in cerebellar Purkinje cells

“…Noxious pinch can cause climbing fiber firing at up to 11 Hz for the duration of the stimulus, lasting several seconds (12). In fact, these experiments were performed in pentobartitone-anesthetized cats and are therefore likely to underestimate the rate of pinch-evoked climbing fiber firing.…”

“…It is likely that DISC will be induced in vivo by climbing fiber excitation, which produces a significant dendritic Ca 2ϩ influx. Noxious pinch has been shown to induce sustained climbing fiber bursting at 11 Hz in anesthetized cats (12). It is likely that in unanesthetized animals, higher peak climbing fiber frequencies could be achieved.…”

Climbing fibres projecting to cat cerebellar anterior lobe activated by cutaneous A and C fibres.

“…The findings that the A,B-and C-fibre-evoked responses were mediated by the same climbing fibres and that the distribution of the A,f-and C-fibre-evoked climbing fibre field potentials was similar indicate that the C-fibre input to climbing fibres projecting to the C 3 zone is somatotopically organized. In a subsequent paper (Ekerot, Oscarsson & Schouenborg, 1987) it will be shown that the receptive field for climbing fibres is the same for tactile and for noxious stimuli.…”

The secondary spikes of climbing fibre responses recorded from Purkinje cell axons in cat cerebellum.

“…This would appear to be sufficient for preventing the occurrence of any conditioning effects. However, olivary discharges have been observed at intervals down to about 40 ms in awake walking cats (Armstrong & Rawson, 1979;Armstrong, Campbell, Edgley, Schild & Trott, 1982), and Ekerot et al (1985) observed that continuous nociceptive stimulation in anaesthetized cats was accompanied by olivary discharge at frequencies exceeding 10 Hz. Eccles et al (1967) discussed the interaction between parallel fibre and climbing fibre input in terms of a 'read-out' hypothesis, where the number of spikes in the c.f.r.…”