Retrograde transneuronal labeling of premotor neurons of horizontal eye movement system in the cat using wheat germ agglutinin conjugated with horseradish peroxidase.

The retrograde transneuronal labeling of premotor neurons of the abducens nucleus was examined by wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) injections into the lateral rectus muscle in the cat. Native horseradish peroxidase injections into the lateral rectus muscle resulted in labeling of neurons in the ipsilateral abducens nucleus and accessory abducens nucleus only. By contrast, when WGA-HRP injections were made into the lateral rectus muscle, retrogradely labeled cells appeared in the mesencephalic central gray, the oculomotor complex, the pontine reticular nuclei, the medial and lateral vestibular nuclei, and the nucleus prepositus hypoglossi, in addition to strong labeling of cells in the ipsilateral abducens nucleus and the accessory abducens nucleus. These findings suggest that portions other than the abducens and the accessory abducens nuclei labeled by WGA-HRP injections into the lateral rectus muscle are transneuronally labeled. The same areas were also labeled by direct injection of a small amount of WGA-HRP into the abducens nucleus. The nonspecific retrograde transneuronal labeling is considered to be applicable to neuroanatomical analysis of origins of afferents to motor regions that innervate the extraocular muscles and consist of several small subdivisions or mixed motoneurons, where it is difficult for conventional tracer techniques to make successfully confined injections.