A pharmacological study on the mechanism of capsaicin-induced corneal lesions.

Research Project

Project/Area Number	62480122
Research Category	Grant-in-Aid for General Scientific Research (B)
Allocation Type	Single-year Grants
Research Field	General pharmacology
Research Institution	Kagoshima University
Principal Investigator	FUKUDA Takeo Faculty of Medicine, Kagoshima University. Professor., 医学部, 教授 (70038694)
Co-Investigator(Kenkyū-buntansha)	SHIMIZU Takao Faculty of Medicine, Kagoshima University. Instructor., 医学部, 講師 (10041336)
Project Period (FY)	1987 – 1988
Project Status	Completed (Fiscal Year 1988)
Budget Amount *help	¥5,900,000 (Direct Cost: ¥5,900,000) Fiscal Year 1988: ¥800,000 (Direct Cost: ¥800,000) Fiscal Year 1987: ¥5,100,000 (Direct Cost: ¥5,100,000)
Keywords	Corneal lesion / Opacity / Capsaicin / Substance P / 6-OHDA / DSP4 / 交感神経 / 化学的交感神経切除 / 6-OHDA
Research Abstract	Capsaicin is known to cause damage to primary sensory afferent neurons, the neurotransmitter of which is believed to be substance P (SP). Following a single subcutaneous injection of capsaicin to neonatal mice, a high incidence of corneal lesions with opacity developed after a long latency. The intensity of the lesions progressed for about 1 month in animal which had received a high dose (50 or 100 mg/kg) of capsaicin. Although the intensity gradually decreased thereafter, 50% of animals still exhibited a visible opacity 6 months after treatment. Similar corneal lesions were also produced in neonatal rats which had been injected with capsaicin. It is suggested that the corneal lesions induced by capsaicin may be due to destruction of the trigeminal nerve. Pretreatment with a subcutaneous injection of 6-hydroxydopamine (6-OHDA) on the lst and 2nd postnatal day or on the 14th and 15th postnatal day led to a marked suppression of the capsaicin-induced corneal lelsions. The content of SP in the ocular anterior segments was decreased, dose-dependently, with capsaicin administration. 6-OHDA decreased the rate of capsaicin-induced reduction of SP. However, this effect of 6-OHDA was too slight to explain the suppression of the corneal lesions. these results suggest that the corneal changes induced by capsaicin are largely inhibited by a decreased activity in the sympathetic system.