Rubrobulbar fibres to the facial nucleus and the lateral reticular nucleus (nucleus of the lateral funiculus). An experimental study in the cat with silver impregnation methods

The present results suggest the presence of a bilateral projection from the mesencephalic reticular formation to the facial nucleus, which could provide an explanation for the paresis limited to the lower facial muscles which is observed in cases of capsular hemiplegia.

Abstract

The projection of the red nucleus to certain nuclei of the medulla has been studied by the silver impregnation methods of Nauta and Glees. The course of the rubro-bulbo-spinal tract at mesencephalic, pontine and medullary levels has been described and illustrated. After unilateral lesions in the red nucleus, degenerated fibres have been observed in the contralateral facial and lateral reticular nuclei. No termination was found in the ambiguous nucleus. In the facial nucleus, only the dorsomedial and intermediate groups receive rubral afferents. In the lateral reticular nucleus, the projection is restricted to the dorsal and lateral parts of the principal portion and to the subtrigeminal portion. No somatotopical organisation of the projection to the latter nucleus could be demonstrated. In addition, the present results suggest the presence of a bilateral projection from the mesencephalic reticular formation to the facial nucleus. In the discussion, the possible functional significance of the rubrofacial projection is analysed. It is also pointed out that the reticulofacial projection could provide an explanation for the paresis limited to the lower facial muscles which is observed in cases of capsular hemiplegia.