Mice lacking sensory neuropeptides do not have altered tear secretion.

Abstract

Abstract: : Purpose: To measure basal and stimulated tear secretion in mice lacking the genes for the sensory neuropeptides αCGRP or substance P. Methods: Adult mice of three strains (C57BL/6J; αCGRP knockout (Salmon et al, 1999), and Tac–1 knockout (Zimmer et al, 1998) were randomized and used in a masked fashion. Tear secretion was measured using a cotton thread with an extreme impregnated in fluorescein (Kurahashi et al, 1977) as a Modified Schirmer Test (MST). Animals were anesthetized (ketamine 100 mg/kg; xilazine 10 mg/kg, i.p.). The cotton thread was kept on the conjunctival sac of each eye for a 7 s period with a 30 min interval between eyes. Results: Basal values of lacrimal secretion showed were not different in the three mice strains studied (C57BL/6J 8.78±1.38mm; αCGRP 6.45±1.12mm; Tac–1 5.22±0.94mm; n=9–10 eyes per group; p=0.111, ANOVA). Preliminary experiments in 10 eyes of each strain, in which noxious mechanical stimulation of the cornea was performed with a von Frey hair of 35mg/mm² and tear secretion measured 1 min afterwards did not show an augmentation of basal secretion values. Conclusions: Basal tear secretion values seem to be preserved in mice strains lacking the genes for the sensory neuropeptides αCGRP or substance P.

Keywords: cornea: tears/tear film/dry eye • neuropeptides • transgenics/knock–outs