Formalin induces biphasic activity in C-fibers in the rat

• Published in: Neuroscience letters 1996-04, Vol.208 (1), p.45-48
• Main Authors: McCall, W.D., Tanner, Kimberly D., Levine, Jon D.
• Format: Article
• Language: English
• Subjects: Action Potentials - drug effects; Animals; Biological and medical sciences; Dorsal root ganglion; Electrophysiology; Formaldehyde - pharmacology; Formalin test; Fundamental and applied biological sciences. Psychology; Hyperalgesia; Male; Nerve Fibers - drug effects; Nerve Fibers - physiology; Neural Conduction - drug effects; Neural Conduction - physiology; Neurons, Afferent - drug effects; Neurons, Afferent - physiology; Nociception; Nociceptor; Nociceptors - drug effects; Nociceptors - physiology; Pain; Primary afferent; Rats; Rats, Sprague-Dawley; Somesthesis and somesthetic pathways (proprioception, exteroception, nociception); interoception; electrolocation. Sensory receptors; Vertebrates: nervous system and sense organs
• ISSN: 0304-3940; 1872-7972
• DOI: 10.1016/0304-3940(96)12552-0

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 μl) 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.