Enkephalin-like immunofluorescence in nerves of the rat iris following systemic capsaicin injection.
A network of nerve fibers with an enkephalin-like immunoreactivity was demonstrated in rat iris whole mounts. Systemic administration of capsaicin in doses which caused partial (5 mg/kg) or complete (50 mg/kg) disappearance of substance P-containing fibers in the iris did not cause degeneration of enkephalin-positive nerve fibers. The enkephalin-immunoreactive network seemed intact also after a capsaicin dose of 250 mg/kg. In fact, the fluorescence intensity of the nerve fibers showing enkephalin-immunoreactivity was often increased three days after a capsaicin injection in a dose of 50 mg/kg. The mechanism behind this effect of capsaicin remains to be elucidated, but could be due either to a direct effect on the enkephalin-positive nerves or involve the disappearance of substance P nerves and/or a simultaneous inflammatory response. However, an increased fluorescence intensity of the enkephalin-immunoreactive fibers was sometimes seen also without capsaicin treatment.
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D004745:Enkephalins / Q000096:biosynthesis*; D005260:Female; D005455:Fluorescent Antibody Technique; D007498:Iris / Q000294:innervation*; D009412:Nerve Fibers / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013373:Substance P / Q000096:biosynthesis
D004745:Enkephalins; D013373:Substance P; D002211:Capsaicin