Topical Mydriatics Affect Light-Evoked Retinal Responses in Anesthetized Mice

Abstract

Purpose To characterize effects of muscarinic antagonist, atropine (A), and α-adrenergic agonist, phenylephrine (P), on mydriasis and light-evoked signaling in mice anesthetized by ketamine and xylazine (K+X). Methods Pupillary areas of anesthetized C57BL/6 mice were measured with or without topical application of either A or A+P. Dark-adapted ERGs were recorded from 2–4 month old C57BL/6 and 7.5 month old albino hrhoG/hrhoG mice following 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. Results K+X anesthesia resulted in maximal 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 two-fold enhancement in 1 h. Recordings with 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 or K + X + A, was converted to a GABA-sensitive response with two electropositive components with A+P after K + X. Conclusion Topical administration of A, and P together, but not separately in presence of K+X, leads to a slow, dramatic enhancement of a- and b-waves by an unknown mechanism independent of pupil dilatation.

In vivo electroretinographic studies of the role of GABAC receptors in retinal signal processing

“…Pupils were fully dilated with topical atropine 0.5% and phenylephrine 2.5%. ERGs were recorded after the response amplitude had reached full growth and had stabilized (Mojumder and Wensel 2010). Body temperature was maintained between 36.5 and 37°C with a thermostatically controlled blanket (CWE Inc.).…”

Evaluating Retinal Toxicity of Intravitreal Caspofungin in the Mouse Eye

“…2) as was done in another study 40: $$V=\frac{{\mathrm{normalV}}_{\text{max}}*I}{(I+I_{0.5})}$$ where, V = ERG response amplitude, V max = the maximum amplitude of the response, I 0.5 = flash energy that elicits a half-maximal response, and I = flash energy that elicits the response, V .…”

“…For examining the scotopic (rod-driven) b-wave, only those responses to flash energies between −3.5 to 0 log sc td s were used to produce the fit, in order to reduce the effects of the scotopic threshold responses (STRs) in the fit for low energies and to minimize the influence of the cone-driven responses at higher energies 40 (Fig. 2).…”

“…Briefly, after overnight dark-adaptation in a ventilated light-tight box, animals were prepared for recording under red illumination [lightemitting diode (LED),> 620 nm]. To obtain consistent and maximal pupillary dilatation without causing ERG amplitude growth during the recording, pupils were fully dilated with a single mydriatic: topical atropine (0.5%) before anesthesia 40. The mice were anesthetized with a single intraperitoneal injection of ketamine (70 mg/kg) and xylazine (7 mg/kg; both drugs from Vedco).…”

Using the Electroretinogram to Assess Function in the Rodent Retina and the Protective Effects of Remote Limb Ischemic Preconditioning

“…The pupils should be a standard size; this is achieved with a mydriatic, applied as eye drops, to achieve maximal dilation. In rodents, atropine or phenylephrine is used 23 . The hydration of the cornea is maintained by application of a carbomer polymer prior to recordings; this also stabilises electrical conductance between the positive electrode and cornea.…”