Are the thalamic projections of nucleus Z of the medulla oblongata reorganized after partial deafferentation of the ventrolateral nucleus of the thalamus?

The possible plastic reorganization of projections from the somatosensory relay nucleus Z of the cat medulla oblongata to the partially deafferented ventrolateral nucleus of the thalamus was studied by retrograde labeling with horseradish peroxidase. Partial deafferentation of the ventrolateral nucleus of the thalamus was produced by prior (three months) electrolytic destruction of the contralateral cerebellar interpositus nucleus or the lateral vestibular nucleus of Deiters. The results demonstrated local intense labeling of a group of neurons in nucleus Z, and there was a small group of labeled neurons in cell group x of the vestibular complex projecting to the ventrolateral nucleus of the thalamus, where these projections were found to overlap with those from the cerebellar nuclei. After lesioning of the cerebellar interpositus nucleus or lateral vestibular nucleus of Deiters, ipsilateral projections in the monosynaptic circuit consisting of nucleus Z and the ventrolateral nucleus of the thalamus did not form. The absence of reorganization of projections from nucleus Z to the ventrolateral nucleus of the thalamus in terms of the formation of ipsilateral projections may be associated with its being part of the somatosensory relay nucleus, which is specialized for relaying and transmitting information strictly of the specific proprioceptive modality.

Reorganization of the vestibulothalamic projections in lesions to the interpositus nucleus of the cerebellum and the vestibular nucleus of Deiters.

The potential for plastic reorganization in the vestibulothalamic system was studied in adult cats. Preliminary (three months) lesioning of the contralateral nucleus interpositus of the cerebellum or the lateral vestibular nucleus of Deiters led to reorganization of vestibulothalamic projections with formation of ipsilateral projections to the ventrolateral nucleus of the thalamus from the nuclei of the vestibular complex, along with changes in the normal representation of the contralateral projections of the vestibular complex to this thalamic nucleus. The distribution and morphological composition of cells in the vestibular nuclei forming the new projections to the ventrolateral nucleus of the thalamus were studied.