The Cortico-Thalamic and -Bulbar Projections from the Somatic Sensory Face Area in the Rat

Abstract

I. Cortical fibers from somatic sensory face area (S I-f) were studied with silver staining technic. S I-f in rat cerebral cortex was confirmed by the record of evoked potentials following the mandibular incisor pulp stimulation.
II. The cortico-thalamic fibers from S I-f ipsilaterally terminated in VPM. Preterminal degenerations could be hardly observed in VA, PF-CM complex and PO from S I cortex.
III. The degenerating terminals of the cortical fibers from S I-f were shown contralaterally in the superior and spinal trigeminal nuclei, except for the rostral half of the superior nucleus and the part caudal to level of the pyramidal decussation in the caudal spinal nucleus. At the level of the pyramidal decussation, some degenerated fibers were found to terminate in the formatio reticularis adjoining to this nucleus.
IV. Termination to the nucleus of tractus solitarius was also recognized in its oral part. Almost no degenerating fibers proceeding into the cuneate nucleus were found.
V. The cortical projections from S II are recognized in the thalamic reticular nucleus, VA, VPM, VPL and the medial geniculate nucleus. In PO, only a few degenerating terminals were recognized. On the other hand, degenerated fibers emerging from M I-f showed the presynaptic terminals in the reticular thalamic nucleus, the lateral part of the anterior ventral thalamic nucleus and the subthalamic region. And also, in the pontine and bulbar reticular formation, the degenerating terminals from M I-f were also recognized in the part adjacent to the sensory trigeminal nucleus, while terminations could not be observed in the trigeminal motor, facial and the hypoglossal nuclei.
VI. Some discussions on the terminal distribution of the degenerating fibers were made to compare with results of other animal species.