Innervation of the iris by individual parasympathetic axons in the adult mouse.

Abstract

SUMMARY1. Ciliary neurones were identified electrophysiologically in isolated ganglia and the projection of individual axons to the intrinsic muscles of the eye determined by labelling identified cells with horseradish peroxidase (HRP).2. The ciliary ganglion of the adult mouse contains 80-100 parasympathetic neurones clustered at the point where the oculomotor nerve branches to supply the medial and inferior rectus. 3. These nerve cells show varying degrees of dendritic complexity (zero to six primary dendrites) and differing degrees of innervation by preganglionic axons (one to seven inputs). Cells with more complex dendritic arborization generally receive synaptic input from commensurately larger numbers of preganglionic axons.4. The axons of individually labelled cells give rise to varicose terminals in the iris and ciliary body; in most cases a single parent axon branches only after entering the iris, producing a network of terminals in the region of both the sphincter and the antagonist dilator muscle. Cells with both simple and complex dendritic geometry show this pattern of axonal arborization.5. The usual net effect of stimulating a single ciliary ganglion neurone through an intracellular electrode is constriction of the pupil. Since the terminals of individual ciliary ganglion neurones are commonly distributed to both the sphincter and dilator regions of the iris, impulses invading the terminals of a single ciliary neurone cause a contraction of the sphincter muscle, perhaps accompanied by a simultaneous relaxation of the dilator.6. Direct examination of individually labelled neurones has revealed details of the pattern of parasympathetic axon distribution to the iris, thus accounting for the origin of cholinergic terminals in the dilator, classically considered to be primarily a target of adrenergic sympathetic neurones.

Target specificity of neuropeptide Y-immunoreactive cranial parasympathetic neurons

“…It is conceivable that the NPY-immunoreactive neurons in the rat ciliary project to targets other than the iris and ciliary body. However, it has been shown in mouse, at least, that ciliary nerve terminals labeled anterogradely by application of HRP to the ganglion are found exclusively in the iris and ciliary body (Jackson, 1986). Hence, the present results suggest that most NPY-immunoreactive neurons in the ciliary do not normally transport immunocytochemically detectable levels of NPY immunoreactivity to their terminals.…”

Axosomatic synapses of the rat ciliary ganglion

“…reflection of the simplicity of the target as the ciliary ganglion innervates the smooth muscle of the ciliary body and iris (Huhtala et al, 1976;Jackson, 1986;Marfurt and Ellis, 1993;Wigston, 1983). Indeed, the cells of the rabbit ciliary ganglion are considered functionally equivalent in the sense that most (94%) respond to retinal illumination with an increase in firing rate (Johnson and Purves, 1983).…”

Catecholaminergic properties of cholinergic neurons and synapses in adult rat ciliary ganglion

“…The ciliary ganglion was decentralized or removed surgically through an incision in the conjunctiva at the inferior pole of the globe of the eye. Blunt separation of the medial and inferior rectus muscles exposed the oculomotor nerve within the orbit at the place where it branches to innervate these 2 muscles (see diagram in Jackson, 1986); the ciliary ganglion is located at this branch point and receives input from preganglionic axons running in the oculomotor nerve. Preganglionic inputs were severed by identifying the ganglion and cutting the oculomotor nerve approximately 5 mm centrally.…”