C-fos induction in rat superficial dorsal horn following cutaneous application of noxious chemical or mechanical stimuli.
The method of c-fos immunodetection was used to map the distributions of neurons in the lumbar spinal dorsal horn that were activated following intracutaneous (i.c.) microinjection, or iontophoretic application, of different irritant chemicals to the lateral hindpaw of rats. Microinjections (1 microl) of histamine, serotonin (5-HT), nicotine, capsaicin, or formalin each elicited similar distributions of Fos-like immunoreactivity (FLI) in laminae I-II of the ipsilateral superficial dorsal horn, with little or no FLI in deeper laminae or contralaterally. In laminae I and II, FLI cell counts were significantly higher following i.c. histamine, 5-HT, capsaicin, formalin, and noxious pinch, compared to i.c. saline controls. Capsaicin-evoked FLI was dose-dependent. Multivariate analysis of variance revealed no significant difference in spatial distributions of FLI induced by any of the chemical or pinch stimuli. Iontophoretic application of histamine, 5-HT, or nicotine also elicited similar distributions of FLI in the superficial dorsal horn, and cell counts of FLI were significantly higher compared to controls receiving iontophoretic vehicle (methyl cellulose). These results indicate either that individual laminae I-II neurons are activated by each of the irritant chemicals, or that neurons selectively responsive to a given irritant are comingled without any apparent laminar segregation.
Section of Neurobiology, Physiology and Behavior, University of California, Davis, 1 Shields Avenue, Davis, CA 95616, USA.
Steven L
SL
Jinks
Christopher T
CT
Simons
Jean-Marc
JM
Dessirier
Mirela Iodi
MI
Carstens
Joseph F
JF
Antognini
E
E
Carstens
D000279:Administration, Cutaneous; D000818:Animals; D007478:Iontophoresis; D007509:Irritants / Q000008:administration & dosage*; D008297:Male; D008845:Microinjections; D010812:Physical Stimulation / Q000379:methods; D020671:Posterior Horn Cells / Q000187:drug effects / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley
D007509:Irritants; D016760:Proto-Oncogene Proteins c-fos