THE AFFERENT PATH OF THE PUPILLODILATOR REFLEX IN THE CAT

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Abstract
The pupillodilatation resulting from sciatic, splanchnic and in some instances trigeminal nerve stimulation was observed after various lesions of the spinal cord and brain in lightly anesthetized cats. This response is known to result from inhibition of oculomotor constrictor activity; the present study adds the observation that destruction of parts of the brain above the oculomotor nucleus does not impair the effect, which is evidently completed at the midbrain level. A common intramedullary pathway conveys afferent impulses from each of the sources studied to the midbrain. This pathway ascends through the lateral funiculus of the spinal cord, traverses the reticular formation of the medulla, gains a paramedian position in the dorsal pontile tegmentum, and ascends through the midbrain in or near the ventral central grey of the aqueduct. This oculomotor inhibitory pathway seems to be distinct from the lateral spinothalamic tract throughout its course and pupillodilatation and pain evoked by stimulating afferent nerves would appear to bear only a coincidental relation to one another.