Neuron Populations Giving Rise to Corticothalamic Projections to the Partially Deafferented Ventrolateral Nucleus of the Thalamus

Abstract

The characteristics of the distribution and morphological composition of neuron populations in the motor cortex projecting to the cerebellar recipient site, the ventrolateral nucleus of the thalamus, after its partial deafferentation were studied in adult cats. Partial deafferentation of the ventrolateral nucleus was produced by prior (three months) electrolytic lesioning of the contralateral intermediate nucleus of the cerebellum. A retrograde axonal horseradish peroxidase transport method with local administration of marker into the ventrolateral nucleus of the thalamus was used. All labeled neurons were members of the populations of nonpyramidal and pyramidal neurons, and most were of small or intermediate size and were located in the deep cortical layers – the lower subdivision of layer V and, mainly, layer VI. Labeled neurons were seen in cortical fi elds 4γ and 6αβ. These data demonstrate the absence of any structural reorganization of cortical projections to the deafferented ventrolateral nucleus of the thalamus. It is suggested that this is due to the high level of specialization of this movement program-triggering system. Neuroplastic changes were apparent in anomalous transformations of the proximal parts of dendrites and the presence of larger numbers of “paired” pyramidal neurons than in intact animals.