Change in excitability and phenotype of substance P and its receptor in cat Abeta sensory neurons following peripheral inflammation.
The effect of peripheral inflammation on spontaneous firing and level of substance P (SP) and its receptor in electrophysiologically identified cat Abeta neurons of dorsal root ganglion (DRG) was studied in vivo using a combination of intracellular recording, dye injection and immunohistochemical techniques. Following injection of carrageenan (Carg) into cat hindpaw, the number of Abeta neurons with spontaneous firing was enhanced significantly (42.9%, n=182) in comparison with control (16.8%, n=149, P<0.01). DRG Abeta neurons became less depolarized 2-4 h following Carg injection. After identifying the cell properties, Lucifer Yellow was injected and SP-like immunoreactivity (SP-LI) was then detected. A total of 17% of Abeta sensory neurons exhibited SP-LI in inflammatory cat. We also found in rat DRGs that the number of SP-LI positive large cells (>35 microm) was also significantly increased in Carg-treated DRG (11.8+/-1.2, n=8) compared with untreated DRG (1.8+/-0.8, n=8, P<0.01). In control cat, the topical use of SP in DRG did not induce any response of Abeta neurons. However, in Carg-treated cat, SP depolarized the membrane potential in most Abeta neurons (68.2%, n=22). L668,169, an antagonist of SP receptor, completely blocked the SP-induced responses. Furthermore, repeated application of SP did not induce obvious desensitization of Abeta neurons. These data suggest that peripheral inflammation increased the excitability, SP level and sensitivity of SP receptor of Abeta neurons. Therefore, we concluded that Abeta sensory neurons appear to contribute to inflammatory allodynia.
Xu
G Y
GY
Shanghai Brain Research Institute, Chinese Academy of Sciences, Shanghai 200031, PR China.
Zhao
Z Q
ZQ
D000200:Action Potentials / Q000187:drug effects; D000287:Administration, Topical; D000818:Animals; D002351:Carrageenan; D002415:Cats; D004594:Electrophysiology; D005456:Fluorescent Dyes; D005727:Ganglia, Spinal / Q000166:cytology*; D007150:Immunohistochemistry; D007249:Inflammation / Q000139:chemically induced / Q000503:physiopathology; D007546:Isoquinolines; D008297:Male; D009475:Neurons, Afferent / Q000737:chemistry / Q000378:metabolism*; D010641:Phenotype; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000032:analysis / Q000378:metabolism*; D013373:Substance P / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology
D005456:Fluorescent Dyes; D007546:Isoquinolines; D018040:Receptors, Neurokinin-1; D013373:Substance P; D002351:Carrageenan; C017475:lucifer yellow