NEURONAL CIRCUITRY CONTROLLING THE LENS AND PUPIL

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Equally necessary for normal visual function are the actions of the pupillary iris that control the amount of light reaching the retina, for both its protection and effective functioning, and the actions of the ciliary muscle that produce accommodation of the lens, bringing the world's objects into sharp focus. Impairment of either of these essential, primarily parasympathetic functions causes visual disorders, yet surprisingly little is known about their central neuronal circuitry. Utilizing a structure-function approach, this gap in our knowledge of the anatomy and physiology of these two systems will be eliminated by correlating intracellular recordings from identified neurons with their morphology as revealed by intracellular staining with horseradish peroxidase. Specifically, identified preganglionic motoneurons of the Edinger-Westphal complex responsible for accommodation or pupillary constriction will be distinguished by physiological criteria and intracellularly injected allowing determination of their morphology and location. Secondly, the afferents to these two motoneuron populations will be identified using intracellular recording and staining techniques. Particular emphasis will be placed on electrophysiological and morphological determination of the synaptic relationship between the motoneurons subserving pupillary constriction and two structures: the pretectum and area 20 of visual cortex. Similarly, the synaptic relationship between the motoneurons subserving lens accommodation and two suprabulbar structures, the interpositus nucleus of the cerebellum and Clare-Bishop area of visual cortex, as well as a presumed midbrain accommodation center, will be ascertained. Third, the circuitry underlying the near reflex will be investigated utilizing the combined intracellular approach to study the connectivity between the midbrain convergence center and preganglionic motoneurons subserving both accommodation and pupillary constriction. Finally, the same techniques will be applied to determine the role of the non-motoneurons in the Edinger-Westphal complex. In conclusion, this correlative structure-function approach will provide a better understanding of the neuronal circuitry that controls lens accommodation and pupillary diameter, making greater insight into disorders of these two functions possible.