Central projections of extraocular muscle afferents in cat.

The extraocular muscles (EOMs) of adult cats were injected with wheat germ agglutinin-horseradish peroxidase (WGA-HRP). In addition to motoneurons, labelled cells corresponding to the sensory receptors were found in both the Gasser ganglion and the mesencephalic trigeminal nucleus. Central transganglionic terminals were observed in the pars interpolaris and caudalis of the spinal trigeminal nucleus, in the paratrigeminal nucleus, and in the dorsal horn of the cervical spinal cord. Double labelling experiments were carried out with either Fast blue or Complex gold tracer, injected in the EOM, and either Diamidino yellow or HRP tracer injected in the cervical dorsal horn. Some Gasser ganglion neurons were found to contain both tracers, providing evidence that the transganglionic terminals are localized in the cervical segments of the spinal cord.