Formalin induces biphasic activity in C-fibers in the rat.
While the formalin test is a widely used behavioral model of tonic chemogenic pain, little is known about the responses of primary afferent nociceptors to formalin. Formalin (2.5%, 50 microliters) was injected either directly in or adjacent to the mechanical receptive fields of single C-fibers isolated from the saphenous nerve of pentobarbital-anesthetized rats. The average formalin-evoked response in C-fibers (n = 29) over time was biphasic. This biphasic time course of the C-fiber response to formalin is similar to that of the behavioral response in the awake animal and is compatible with the hypothesis that increased C-fiber activity contributes to the behavioral response in phase 2, as well as in phase 1 of the formalin test.
McCall
W D
WD
School of Dental Medicine, SUNY, Buffalo 14214-3008, USA.
Tanner
K D
KD
Levine
J D
JD
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004594:Electrophysiology; D005557:Formaldehyde / Q000494:pharmacology*; D008297:Male; D009412:Nerve Fibers / Q000187:drug effects / Q000502:physiology*; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley
D005557:Formaldehyde