Figure 8. Physiological properties of a type IV neurone.

Aa, nociceptive stimulation of the contralateral hind paw (*, c-foot) elicits a burst of action potentials and little alteration of resting arterial blood pressure (AP). Noxious stimulation applied to the ipsilateral hind paw (i-foot) and tip of the tail (t-tail) has no effect while pinch of the root of the tail (r-tail) also elicits a burst of spikes. AP elevation (aortic occlusion) does not inhibit the toe pinch-evoked burst. Ab, expanded time scale view of the burst of spikes elicited by the second, fourth and fifth applications of noxious contralateral paw pinch. B, collision of the antidromic spike (a) elicited by hypothalamic stimulation (arrow) with the spontaneous spike (s). In the first and third traces, the delay between the spontaneous spike and the hypothalamic stimulus exceeds the critical interval for collision. Reduction of the delay between the spontaneous spike and the hypothalamic stimulus to the critical interval results in collision of the antidromic spike. C, spinal cord stimulation results in only orthodromic stimulation of the cell.