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. 2019 Feb 22;10:129. doi: 10.3389/fneur.2019.00129

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Copyright © 2019 Kelbsch, Strasser, Chen, Feigl, Gamlin, Kardon, Peters, Roecklein, Steinhauer, Szabadi, Zele, Wilhelm and Wilhelm.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Targets of drugs in the neuronal network controlling the pupil. The pupil is an aperture in a diaphragm, the iris. The size of the pupil reflects the interaction between the circular sphincter muscle and the radial dilator muscle. The sphincter receives a parasympathetic and the dilator a sympathetic output. Both autonomic outputs consist of serially linked preganglionic and postganglionic neurones that are under the influence of premotor autonomic neurones. The premotor neurones channel the influence of other brain structures (e.g., cortex) and light to the preganglionic neurones. Premotor neurones: SCN: suprachiasmatic nucleus (hypothalamus); PVN: paraventricular nucleus (hypothalamus); LC: locus coeruleus (brainstem: pons); OPN: olivary pretectal nucleus (pretectum). Preganglionic neurones: IML: intermediate lateral column (spinal cord); EWN: Edinger-Westphal nucleus (brainstem: midbrain). Postganglionic neurones: SCG: superior cervical ganglion; GC: ciliary ganglion. Arrows are neuronal connections, red arrows are excitatory connections with identified neurotransmitters (Glu, glutamate; NA, noradrenaline; Ach, acetylcholine). Drugs can be applied topically to the surface of the cornea to affect the iris and the noradrenergic and cholinergic neuro-effector junctions, or systemically when they can affect any part of the central neuronal network. It should be noted that topically applied drugs may get into the systemic circulation leading to systemic effects, and systemically applied drugs may also affect the iris directly.