Hiura_2004_Okajimas.Folia.Anat.Jpn_81_75

Little is known whether capsaicin affects on the nonspecific acetylcholinesterase (NsAchE) positive nerves in the cornea. To examine this point, the density of the corneal nerve fibers stained with NsAchE method was compared with that of control. Capsaicin (50 mg/kg) was injected once into the dorsal skin of rats at 2 day after birth. As controls, a vehicle was similarly injected into animals of the same age. At 5 (n = 3), 17 (n = 4), 45 (n = 4) and 75 (n = 3) days after treatment, the bilateral corneas were excised from capsaicin treated (n = 14) and age-matched control animals (n = 14). The entire subepithelial corneal nerves stained in whole mount preparations were hand traced. Their density was represented as mm/mm2 by converting the total areas of the nerve fibers into the total length of them using computer image analysis system. No significant differences in the nerve fiber density were seen in the control and capsaicin-treated corneas at the survival times examined. Even high doses of neonatal capsaicin injection (total: 150 mg/kg) no NsAchE-reacted corneal nerves showed a significant decrease. However, the time of wiping by instillation of 100 microM capsaicin onto the corneas severely reduced (analgesia to chemical irritant) in the neonatal capsaicin-treated rats (50 mg/kg, n = 13) compared with those of controls (n = 13) at 17, 45 and 75 day survivals. This was closely associated with the decrease of PGP-ir intraepithelial nerve fibers. The corneal nerves reacted with the NsAchE seemed to be capsaicin resistant and have a functional property except the chemical nociception.