Course and termination of fibres from the nucleus Z of the medulla oblongata. An experimental light microscopical study in the cat

Abstract

Summary The nucleus z of Brodal and Pompeiano, recently shown to be the bulbar relay in the pathway of hind limb group I muscle afferents to the cerebral cortex in the cat, was subjected to experimental lesions in 9 cats. Ensuing degeneration was studied by light microscopy in Fink-Heimer or Nauta impregnated serial transverse sections from the thalamus. In one cat with a restricted lesion of the nucleus z the degenerating fibres were followed from the area of the lesion up to the thalamus. They had a course similar to that of the internal arcuate fibres, penetrated the ipsilateral inferior olivary nucleus at caudal and middle olivary levels, crossed the midline and reached the medial subdivision of the medial lemniscus. Here they could be traced further rostrally to the thalamus. At caudal thalamic levels degenerating fibres traversed the ventral parts of the nucleus ventralis posterior inferior (VPI). Thence most fibres passed in a narrow strip bordering the nucleus ventralis posterior lateralis (VPL) and the lamina medullaris externa (EML) and reached more rostral regions. Some fibres did, however, pass medial and dorsal to the VPL. Terminal fibres were found rostrally in the thalamus in a continuous area extending approximately from the level of the rostral pole of the lateral geniculate body (GLD) to about 1 mm rostral to the rostral pole of the VPL. This area comprised the ventrolateral part of the nucleus ventralis lateralis (VL) and a small portion of the rostrolateral part of the VPL 1 . Some degenerating fibres were observed in the nucleus centrum medianum (CM) and the medial part of the posterior group of nuclei (PO m ). However, it could not be determined whether or not they were terminal. No degenerating fibres were seen in the thalamus ipsilateral to the medullary lesions.