Parasympathetic control of the pupillary light response in the red‐eared slider turtle (Pseudemys scripta elegans)

Abstract

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.

Sympathetic influence on the pupillary light response in three red‐eared slider turtles (Trachemys scripta elegans)

“…All care and procedures of turtles were performed in accordance with the guidelines of the Institutional Animal Care and Use Committee (IACUC) at Lafayette College. Full details of turtle care, apparatus, pupillometry, drug treatment protocol, and data analysis are described elsewhere 7 …”

“…Three (0.58–1.20 kg) red‐eared slider turtles, Trachemys scripta elegans , formerly known as Pseudemys scripta elegans , were subjects. Two of these three turtles were the same subjects that were used in a prior study 7 where vecuronium bromide was applied alone.…”

“…Drug application again was four times at 15 min intervals, except that vecuronium bromide was applied first then followed 2 min later with phenylephrine (concentrations as above). At a concentration of 0.4% for vecuronium bromide, four applications of 0.04 mL delivered 0.64 mg. At this dose in turtles, 7 vecuronium bromide acts as a parasympatholytic on nicotinic cholinergic receptors to produce mydriasis.…”

“…To quantify the rates of pupillary dilation in drug‐treated eyes, a time constant equation was used: 5,7,14 …”

“…Although the parasympathetic division plays a role in control, 6 it has not been determined whether the sympathetic division is also involved. Our recent reexamination of the parasympathetic innervation of the turtle iris found that corneal application of the nicotinic cholinergic antagonist vecuronium bromide causes mydriasis and the muscarinic cholinergic antagonist atropine does not, 7 suggesting that cholinergic receptors of the sphincter pupillae in turtles are more similar to birds and not to mammals, as once thought 6 …”