Topical mydriatics affect light-evoked retinal responses in anesthetized mice.
OBJECTIVE
To characterize effects of the muscarinic antagonist atropine (A) and the alpha-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 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.


RESULTS
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 gamma-aminobutyric acid (GABA)-sensitive response with two electropositive components with A+P after K+X.


CONCLUSIONS
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.
Mojumder
Deb Kumar
DK
Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, USA.
Wensel
Theodore G
TG
D000287:Administration, Topical; D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage; D019162:Anesthetics, Combined / Q000008:administration & dosage*; D000778:Anesthetics, Dissociative / Q000008:administration & dosage; D000818:Animals; D001285:Atropine / Q000008:administration & dosage*; D003623:Dark Adaptation; D004338:Drug Combinations; D004596:Electroretinography / Q000187:drug effects*; D007649:Ketamine / Q000008:administration & dosage; D008027:Light; D051379:Mice; D008810:Mice, Inbred C57BL; D018613:Microscopy, Confocal; D018727:Muscarinic Antagonists / Q000008:administration & dosage; D009184:Mydriatics / Q000008:administration & dosage*; D010656:Phenylephrine / Q000008:administration & dosage*; D011680:Pupil / Q000187:drug effects*; D012160:Retina / Q000528:radiation effects*; D012162:Retinal Degeneration / Q000503:physiopathology; D013997:Time Factors; D014991:Xylazine / Q000008:administration & dosage
D000316:Adrenergic alpha-Agonists; D019162:Anesthetics, Combined; D000778:Anesthetics, Dissociative; D004338:Drug Combinations; D018727:Muscarinic Antagonists; D009184:Mydriatics; D010656:Phenylephrine; D014991:Xylazine; D007649:Ketamine; D001285:Atropine