Intradermal 5-HT induces Fos expression in rat dorsal horn neurons not via 5-HT3 but via 5-HT2A receptors.
We investigated the effects of peripherally administered 5-HT on the secondary neurons in the spinal cord of rats using Fos-like immunoreactivity (FLI) as a marker of neuronal activation. The intradermal administration of 5-HT (30, 60 microg) induced a large number of FLI neurons in the ipsilateral dorsal horn. In animals given 5-HT2A receptor agonists (DOI: 0.28 to 2.8 micromol/kg, alpha-methyl 5-HT: 0.28 to 2.8 micromol/kg) intradermally, immunoreactive neurons were evoked in the same manner as those given 5-HT. Other agonists, including 5-HT3 receptor agonists (m-CPG: 16 to 32 micromol/kg, 2-methyl 5-HT: 0.0028 to 2.8 micromol/kg), did not induce FLI neurons at any dose examined. Furthermore, 5-HT2A receptor antagonist (ketanserin: 1 mg/kg, i.p.) suppressed the expression of FLI in the dorsal horn caused by peripheral 5-HT, but 5-HT3 receptor antagonist (tropisetron: 1 mg/kg, i.p.) did not. These findings suggest that the 5-HT-induced nociceptive response is mediated by 5-HT2A receptors in the periphery.
Doi-Saika
M
M
Department of Anatomy and Neurobiology, Wakayama Medical College, Japan.
Tokunaga
A
A
Senba
E
E
D000818:Animals; D007150:Immunohistochemistry; D007271:Injections, Intradermal; D008297:Male; D009474:Neurons / Q000378:metabolism*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013116:Spinal Cord / Q000166:cytology / Q000378:metabolism*
D016760:Proto-Oncogene Proteins c-fos; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin