Discharge patterns of nociceptive primary afferent fibres in the rat coccygeal nerve after UVA-light exposure
Themistocleous A., Kamerman P., Mitchell D.
We have shown that administration of the local anaesthetic bupivacaine into the base of rats' tails prevents the development of hyperalgesia induced by UVA-light to a noxious thermal challenge, but not to noxious mechanical challenges. The aim of this study was to determine whether exposure of rats' tails to UVA-light altered the responses of Aδ- and C-fibres innervating the tail to noxious mechanical and noxious thermal challenges. We dissected the right ventral coccygeal nerve in Sprague-Dawley rats that had their tails exposed to, or shielded from, UVA-light 24-h earlier. Single afferent Aδ- and C-fibres receptive fields were located and the response of a fibre to noxious blunt (3.9 N bar algometer) and punctate (rat toothed forceps) mechanical challenges, as well as a noxious thermal (49 °C) challenge was measured. In rats exposed to UVA-light, the peak firing rates and areas under the curve of post-challenge histograms of Aδ- and C-fibres evoked neural activity were increased when noxious blunt and punctate challenges were applied to the rats' tails. However, the peak firing rate and areas under the curve of post-challenge histograms of C-fibre evoked neural activity, which were responsive to noxious thermal challenges, were not increased after UVA-light exposure. We have shown that the Aδ- and C-fibres that encode for noxious punctate and blunt challenges were sensitized after UVA-light exposure, but C-fibres responsible for encoding noxious thermal challenges were not sensitized by UVA-light exposure. © 2009 European Federation of International Association for the Study of Pain Chapters.