Fine structural innervation of the dilator muscle of the iris of the albino guinea pig studied with permanganate fixation

Abstract

Six per cent potassium permanganate fixation was used to study the fine structural autonomic innervation of the dilator muscle of the iris of albino guinea pigs. Axons containing granular vesicles and other axons containing exclusively agranular vesicles within the same nerve bundles were present in the iris dilator muscle in a 2 : 1 proportion. In those axons containing granular vesicles, these vesicles numbered 90% of the total. The granular vesicles were 400–600in diameter with granules of 200–300in diameter. A few vesicles of 800–950in diameter with 400–600granules of variable density were also present. Axons with agranular vesicles contained a homogenous population of agranular vesicles of 350–450in diameter, and represented a third of the total number of axons in a given nerve bundle. The relatively uniform granulation of vesicles in the axons with granular vesicles and their degranulation after sympathetic denervation and administration of reserpine supports the interpretation that these axons represent adrenergic fibers. The consistent morphologic picture of adrenergic nerve fibers obtained with permanganate fixation is useful in correlating morphologic and physiologic studies. The finding of uniform agranularity of agranular cholinergic vesicles in axons within the same nerve bundle, which could contain other axons bearing predominantly granulated vesicles, taken together with pharmacologic proof that these latter are adrenergic suggests a dual innervation to the iris dilator muscle.