Capsaicin-induced corneal lesions in mice and the effects of chemical sympathectomy.

Effects of chemical sympathectomy on corneal changes induced in mice by a s.c. injection of capsaicin were investigated. Pretreatment with a s.c. injection of 6-hydroxydopamine (6-OHDA) on the 1st and 2nd postnatal day or on the 14th and 15th postnatal day led to a marked suppression of the capsaicin-induced corneal lesions. This suppressive effect also was evident in case of administration after capsaicin treatment. Intraventricular injection of 6-OHDA had a slight, transient effect. DSP4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine], another potent substance used for sympathetic denervation, had a suppressive effect similar to that of 6-OHDA. The concentration of capsaicin in tissues of the head was unaltered with 6-OHDA. The content of substance P (SP) in the ocular anterior segments was decreased, dose-dependently, with capsaicin administration. Neonatal administration of 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, as the intensity score of lesions with a large dose of capsaicin after 6-OHDA was lower than that with a small dose of capsaicin without 6-OHDA, whereas SP content in the former was still much lower than that in the latter. On the other hand, the content of norepinephrine in the ocular tissues was decreased in the presence of 6-OHDA but not capsaicin. These results suggest that the corneal changes induced by capsaicin are largely inhibited by a decreased activity in the peripheral sympathetic system.