Differentiation between A delta and C fibre evoked nociceptive reflexes by TTX resistance and opioid sensitivity in the cat

Abstract

The contribution of nociceptive A delta-fibres and C-fibres of the central pad of the foot to nociceptive spinal flexor reflex pathways (FM-type) and to nociceptive excitatory reflex pathways to foot extensors (non-FRA type) was investigated in high spinal cats. Persisting effects after complete blocking of A-fibres by tetrodotoxin (TTX) application were thus attributed to nociceptive C-fibres. The results revealed that both A delta and C-fibre afferents contributed to nociceptive reflexes of a FM-pattern and of a non-FRA pattern. Thereby, the effects of A delta-fibres were evoked with a distinctly shorter delay than those of C-fibres. Furthermore, A delta-fibres partly exerted a significant inhibitory influence on the C-fibre action in FRA and non-FRA pathways. Treatment with different opioid receptor agonists (DAMGO and DSLET) and subsequently with naloxone revealed that a distinct part of the opioid action on nociceptive reflex pathways of the FRA-type and of the non-FRA type was evidently exerted via A delta-fibres. (C) 2010 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved.