Cerebello-thalamo-cortical system

II Morphology of physiologically identified thalamocortical neurons in the ventrolateral nucleus of the thalamus

Abstract

The thalamo-cortical relay neurons (TCR) of the nucleus ventralis lateralis of the cat's thalamus were examined after the intracellular injection of horseradish peroxidase, and 20 TCR neurons were reconstructed three dimensionally.
(1) TCR neurons are medium or large spheroidal cells. The dendritic field is about 380630μm, and the diameter of the cell bodies is about 2050μm. The cells have 48 principal dendrites and the dendrites arborize near the cell bodies. Finally the branches terminate in 73-148 terminal knobs. All dendrites have many spines except in their initial parts.
(2) The axons of TCR neurons originate from the cell bodies and run antero-laterally, pass through the reticular nucleus of the thalamus, and enter the internal capsule. The axon collaterals are observed within the reticular nucleus of the thalamus. It seems that these collaterals are involved in recurrent collateral inhibition.
(3) The axons of TCR neurons begin to branch in the white matter just below the gray matter of the motor cortex, and several branches enter the gray matter. In the gray matter the branches bifurcate several times and finally terminate mainly in the third cortical layer, and also some in the first layer.
The projection area of the axons of single TCR neuron in the motor cortex is more than 2.0mm×2.0mm