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This Article Full Text Full Text (PDF) Supplemental data All Versions of this Article: 576/2/547    most recent jphysiol.2006.117754v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by McMullan, S. Articles by Lumb, B. M. Search for Related Content PubMed PubMed Citation Articles by McMullan, S. Articles by Lumb, B. M. Related Collections Neuroscience

¹ Hypertension and Stroke Research Laboratory, University of Sydney, Australia
² Department of Physiology, University of Bristol, UK

The aim of this study was to further understand the central processing of inputs arising from unmyelinated and myelinated nociceptors by (i) determining the response characteristics of Class 2 dorsal horn neurones to preferential activation of C- and A-fibre heat nociceptors, and (ii) investigating the control exerted by the dorsolateral/lateral region of the midbrain periaqueductal grey (DL/L-PAG) on C- and A-fibre-evoked responses of these neurones. The use of different rates of skin heating to preferentially activate unmyelinated (C-fibre; 2.5°C s^–1) versus myelinated (A-fibre; 7.5°C s^–1) heat nociceptors revealed that, in response to C-nociceptor activation, Class 2 neurones encode well only over the first 5°C above threshold, and that at higher temperatures responses decline. In contrast, responses to A-nociceptor activation are linear and encode skin temperature over more than 10°C, and almost certainly into the tissue-damaging range. PAG stimulation raised thresholds and decreased significantly the magnitude of responses to A- and C-nociceptor activation. However, differences were revealed in the effects of descending control on the relationships between skin temperature and neuronal firing rate; the linear relationship that occurred over the first 5°C of slow rates of skin heating was no longer evident, whereas that to fast rates of skin heating was maintained over the entire range, albeit shifted to the right. These data indicate that the sensori-discriminative information conveyed in A-fibre nociceptors is maintained and that the information from C-nociceptors is lost in the presence of descending control from the DL/L-PAG. The data are discussed in relation to the role of the DL/L-PAG in mediating active coping strategies.

(Received 21 July 2006; accepted after revision 14 August 2006; first published online 17 August 2006)
Corresponding author S. McMullan: Hypertension and Stroke Research Laboratory, Royal North Shore Hospital, St Leonards, Sydney, NSW 2065, Australia. Email: smcmullan{at}med.usyd.edu.au

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				J. L. Leith, A. W. Wilson, L. F. Donaldson, and B. M. Lumb Cyclooxygenase-1-Derived Prostaglandins in the Periaqueductal Gray Differentially Control C- versus A-Fiber-Evoked Spinal Nociception J. Neurosci., October 17, 2007; 27(42): 11296 - 11305. [Abstract] [Full Text] [PDF]