J. Martindale et al., Inhibition of C-fibre mediated sensory transmission in the rat following intraplantar formalin, NEUROSCI L, 316(1), 2001, pp. 33-36
Using extracellular recordings from deep dorsal horn neurones in the anaest
hetized rat, the effects of intraplantar (i.pl.) administration of formalin
were examined. Phasic patterns of dorsal horn firing were observed which t
emporally concur with previously described behavioural responses following
Lpl. formalin. However, unexpectedly, formalin abolished C-fibre mediated t
ransmission, and significantly reduced responses to noxious mechanical stim
ulation, while electrically evoked A-fibre responses were unaffected. This
suggests that whilst the first phase formalin response is mediated by direc
t afferent stimulation, the second phase behavioural response is dependant
on a central hyperexcitability of the recipient second-order dorsal horn ne
urones, which may be maintained by peripheral input only from A-fibres. Thi
s study therefore provides further evidence for a centrally-mediated second
ary component of the formalin model, and for the first time, describes loss
of high-threshold C-fibre input to the spinal cord during this phase. (C)
2001 Elsevier Science Ireland Ltd. All rights reserved.