title: Topical mydriatics affect light-evoked retinal responses in anesthetized mice.
abstract: 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.
authors: Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, Texas, USA.
authors: Deb Kumar
authors: DK
authors: Mojumder
authors: Theodore G
authors: TG
authors: Wensel
mesh_terms: 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
chemical_list: 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