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Deb Kumar Mojumder, Theodore G. Wensel; Topical Mydriatics Affect Light-Evoked Retinal Responses in Anesthetized Mice. Invest. Ophthalmol. Vis. Sci. 2010;51(1):567-576. doi: https://doi.org/10.1167/iovs.09-4168.
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To characterize effects of the muscarinic antagonist atropine (A) and the α-adrenergic agonist, phenylephrine (P), on mydriasis and light-evoked signaling in mice anesthetized by ketamine and xylazine (K+X).
Pupillary areas of anesthetized C57BL/6 mice were measured, with or without topical application of A or A+P. Dark-adapted ERGs were recorded from 2- to 4-month-old C57BL/6 and 7.5-month-old albino hrhoG/hrhoG mice after application of A or P singly or in combination, before or after induction of K+X anesthesia. Effects of GABA were tested in the hrhoG/hrhoG mice.
K+X anesthesia resulted in maximum mydriasis that was not enhanced by A or A+P. Dark-adapted b-wave amplitudes (−1.3 log sc td s) after K+X anesthesia were similar with or without A or P. A+P in the presence of K+X produced a slow growth in b-wave amplitude, reaching a plateau of twofold enhancement in 1 hour. Recordings of responses to varying flash energies revealed that the effects of A+P were on the maximum amplitude of the a- and b-waves and not on their sensitivity. Scotopic threshold responses were augmented as well. In photoreceptor-degenerated mice (hrhoG/hrhoG), an electronegative ERG wave recorded with K+X+A, was converted to a γ-aminobutyric acid (GABA)-sensitive response with two electropositive components with A+P after K+X.
Topical administration of A and P together, but not separately, in the presence of K+X, leads to a slow, dramatic enhancement of a- and b-waves by an unknown mechanism independent of pupil dilation.
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