Discharge patterns of nociceptive primary afferent fibres in the rat coccygeal nerve after UVA-light exposure.
We have shown that administration of the local anaesthetic bupivacaine into the base of rats' tails prevents the development of hyperalgesia induced by UV(A)-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 UV(A)-light altered the responses of Adelta- 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, UV(A)-light 24-h earlier. Single afferent Adelta- and C-fibres receptive fields were located and the response of a fibre to noxious blunt (3.9Nbar algometer) and punctate (rat toothed forceps) mechanical challenges, as well as a noxious thermal (49 degrees C) challenge was measured. In rats exposed to UV(A)-light, the peak firing rates and areas under the curve of post-challenge histograms of Adelta- 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 UV(A)-light exposure. We have shown that the Adelta- and C-fibres that encode for noxious punctate and blunt challenges were sensitized after UV(A)-light exposure, but C-fibres responsible for encoding noxious thermal challenges were not sensitized by UV(A)-light exposure.
Themistocleous
Andreas
A
Brain Function Research Unit, School of Physiology, University of the Witwatersrand, Johannesburg, South Africa. andrea_them@yahoo.com
Kamerman
Peter
P
Mitchell
Duncan
D
D000344:Afferent Pathways / Q000503:physiopathology; D000704:Analysis of Variance; D000818:Animals; D004594:Electrophysiology; D006358:Hot Temperature; D006930:Hyperalgesia / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D009431:Neural Conduction / Q000502:physiology*; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013127:Spinal Nerves / Q000503:physiopathology*; D013623:Tail / Q000294:innervation*; D014110:Touch; D014466:Ultraviolet Rays / Q000009:adverse effects*