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Melior Discovery neurophysiology

C-fiber Pain Reflex
C-fibers are small unmyelinated fibers transmitting diffuse pain signals from the periphery to the spinal cord.  Larger and faster myelinated Aδ and A β fibers transmit pain and touch information.  C-fiber pain activity can be selectively evaluated by stimulating the foot-pad and recording reflex activity in the peroneal muscle between 150 and 400 msec following stimulus.  Activity in this pathway can be recorded for several hours allowing within-animal determination of baseline, test article and drug interation effects. 

Figure A: Illustration of C-Fiber Response (CFR):

                                      

Stimulation of the ventral foot pad produces a reflex activation of the peroneus longus muscle consisting of early Aδ and A β nerve fiber responses, followed by the unmyelinated C-fiber response beginning around 150 msec. 

 

Figure B: Recording and Analysis of CFR:

                              

The C-fiber response (CFR) is recorded from the peroneus longus muscle during continuous stimulation of the ventral foot-pad at 6 second intervals. 

 

Figure C: Effect of Morphine on CFR:

                                        

Dose-related effect of morphine on CFR.  Morphine was administered subcutaneously at time 0; n=3 rats/curve.  The CFR was completely inhibited at 10mg/kg for approximately 30 minutes.  Note the increased response at 3mg/kg [1] - this is normal and presumed to result from greater supra-spinal dis-inhibition relative to spinal inhibition at this dose.  The effect of morphine on the CFR is reversed by the opioid antagonist naloxone (not shown). 

 

If you are interested in learning more about C-fiber Pain Reflex testing, please contact models@meliordiscovery.com to start the conversation.