Efferent discharge patterns in the ciliary nerve of rabbits and the pupillary light reflex

Unitary discharges in the efferent ciliary nerves were studied in cervical sympathectomized rabbits. In all, 279 units were recorded and categorized, except 7 units, into the following 3 types from their responses to photic and other stimuli, i.e. type A (170 units), type B (42 units) and type C (60 units). Type A units were characterized by exhibiting excitatory response to ipsilateral eye illumination and the response was closely related to the luminance level. The type A was further classified into AI (excitation), AII (no change) and AIII (inhibition) on the basis of the response to contralateral illumination. It was inferred that the type A was functionally related to active pupilloconstriction. Type B units were characterized by showing an exclusively inhibitory response to ipsilateral and/or contralateral illumination and the inhibition was luminance-dependent. It was therefore assumed that the type B was concerned with active pupillodilation. Type C units were not responsive to light stimulus, though the type C displayed characteristic reflex response to mechanical or thermal stimulus within the receptive field. The reflexive response, however, was not mediated via the oculomotor nerve. In order to confirm the results of the unit analysis, pupillary light reflex was examined. In particular, the consensual reflex varied depending upon individual rabbits. Namely, one became miotic, another mydriatic and a third remained uninfluenced, which corresponded well with the response pattern of the light-sensitive units.