Cerebellar influence on parasympathetic neurones innervating intra-ocular muscles.

Previous work has suggested that cerebellum may control the size of the pupil and transmission in the pathway mediating the pupillary light reflex. In this work we found that electrical stimulation of the cerebellar nuclei (nucleus fastigius and nucleus interpositus bilaterally) evoked a discharge in the short ciliary nerves which innervate the intraocular muscles. The latency was 5.7 msec, which is short enough for a direct excitatory connexion from cerebellar efferents onto the preganglionic neurones in the Edinger-Westphal nucleus. These neurones are controlling the ciliary muscle of the lens system as well as the constrictor muscle of the pupil and it was therefore important to elucidate whether both of these groups participate in the discharge. Studies on interaction between the response to cerebellar stimulation and 'pupilloconstrictor' responses from optic tract fibres as well as recording from individual cells in the ciliary ganglion (identified with diffuse light stimuli) led to the conclusion that the short latency excitation is more or less confined to units controlling accommodation. Cerebellar inhibition (or disfacilitation) of longer latency affects both pupilloconstrictor and accommodation units.