Trigeminal afferent fibers in the trunk of the oculomotor nerve of lambs

Abstract

In lambs, chronic section of the oculomotor nerve at the base of the skull just proximally to the cavernous sinus induced degeneration of some fibers in the central stump, although the peripheral stump contained some normal fibers. On the other hand, chronic section of the ophthalmic branch just distally to the semilunar ganglion was followed by degeneration of a certain number of medium and large caliber fibers in the ipsilateral oculomotor nerve. The presence of trigeminal afferent fibers in the trunk of an oculomotor nerve is supported by electrophysiologic experiments. Single-shock electrical stimulation of the frontal and nasociliary nerves and of the conjunctiva of the superior and inferior eyelids elicited short-latency evoked potentials, not only in the semilunar ganglion but also in the ipsilateral oculomotor nerve at the base of the skull. Such responses did not appear in those animals in which the ipsilateral ophthalmic and maxillary branches of the trigeminal nerve had been chronically cut. Thus, we can affirm that afferent trigeminal impulses enter the brain stem also through the third nerve. The perikarya of such a pathway are localized in the semilunar ganglion; the peripheral processes attain the conjunctiva of the superior and inferior eyelids through the ophthalmic and maxillary branches, and the central processes enter the oculomotor nerve by anastomoses between IIIrd and Vth cranial nerves after a short passage in the two trigeminal branches. The trigeminal nature of these fibers is also shown by the fact that electrical stimulation of the central stump of the IIIrd nerve can influence the dorsal neck muscles in the same way as other trigeminal afferents.