Parasympathetic control of the pupillary light response in the red-eared slider turtle (Pseudemys scripta elegans).
OBJECTIVE
We investigated effects of both vecuronium bromide, a nicotinic cholinergic antagonist, and atropine, a muscarinic cholinergic antagonist, on the pupil of the turtle to determine whether responses to light are controlled by parasympathetic innervations acting on the iris.


METHODS
Three red-eared slider turtles, Pseudemys scripta elegans.


METHODS
Turtles were secured to immobilize their head movements and then inserted into a light-integrating sphere. Both pupils were monitored through small apertures by digital video cameras. Pupil diameters were measured manually with a digital caliper. During each trial, drugs (0.4%) were topically applied, four times at 15 min intervals, to the corneas of each eye. One eye was randomly selected for treatment of the drug while the other, treated with saline (0.9% NaCl), was used as control. Pupil sizes under adaptation to light were tracked after drug or saline applications.


RESULTS
Mean pupillary diameters of eyes treated with vercuronium bromide increased by 28%, reaching peak size in 90 min. Onset of response occurred 20 min after drug application and then increased at a rate having a time constant of 26 min. Recovery began at 120 min after initial application. Atropine had no effect on pupil size. No systemic side effects by drugs were observed in turtles.


CONCLUSIONS
Although atropine does not cause mydriasis, vecuronium bromide does. These results suggest that the parasympathetic system in turtles acts through acetylcholine onto nicotinic receptors to stimulate pupillary light constriction.
Dearworth
J R
JR
Department of Biology, 311 Kunkel Hall, Lafayette College, Easton, PA 18042, USA. dearworj@lafayette.edu
Cooper
L J
LJ
McGee
C
C
D000818:Animals; D001285:Atropine / Q000008:administration & dosage / Q000494:pharmacology; D007498:Iris / Q000187:drug effects / Q000294:innervation / Q000528:radiation effects*; D008027:Light; D009184:Mydriatics / Q000008:administration & dosage / Q000494:pharmacology; D009883:Ophthalmic Solutions / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000528:radiation effects; D010775:Photic Stimulation; D010786:Photoreceptor Cells / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D014426:Turtles / Q000502:physiology*; D014673:Vecuronium Bromide / Q000008:administration & dosage / Q000494:pharmacology
D009184:Mydriatics; D009883:Ophthalmic Solutions; D001285:Atropine; D014673:Vecuronium Bromide