INVOLVEMENT OF VENTROLATERAL ORBITAL CORTEX 5-HT 1-7 RECEPTORS IN 5-HT INDUCED DEPRESSION OF SPARED NERVE INJURY ALLODYNIA

The present study examined the roles of ventrolateral orbital cortex (VLO) 5-HT1, 5-HT2, 5-HT3, 5-HT4, 5-HT5, 5-HT6 and 5-HT7 receptor subtypes in mediating 5-HT-induced antiallodynic actions in the rat spared nerve injury (SNI) pain model. Changes in paw withdrawal threshold (PWT) were measured using von-Frey filaments. Microinjection of 5-HT (2, 5 and 10 mu g, in 0.5 mu l) into the VLO depressed allodynia induced by SNI, and the PWT increased in a dose-dependent manner. Microinjection of selective 5-HT1A, 5-HT2, 5-HT3, 5-HT4, 5-HT5A, 5-HT6 and 5-HT7 receptor antagonists, 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl] piperazine hydrobromide (NAN-190) (10 mu g), cyproheptadine (50 ng), granisetron hydrochloride (granisetron) (10 mu g), 1-[2-[(methylsulfonyl)-amino]ethyl]-4-piperidinyl]methyl1-methyl-1H-indole-3-carboxylate (GR113808) (5 mu g), SB699551 dihydrochloride (SB699551) (10 SB258585 dihydrochloride (SB258585) (2 mu g) or SB269970 hydrochloride (SB269970) (10 pig) into the VLO 5-min prior to 5-HT (10 mu g) injection, all antagonized the 5-HT-induced inhibition of allodynia. In addition, these antagonists applied alone to VLO did not influence allodynia. These results suggest that although 5-HT1-7 receptor subtypes in the VLO do not have a tonic modulatory action on the allodynia induced by SNI, they are involved in mediating the depression of the SNI allodynia produced by injection of 5HT into VLO. (C) 2013 IBRO. Published by Elsevier Ltd. All rights reserved.