Journal of Neuroscience, Vol 5, 1316-1338, Copyright © 1985 by Society for Neuroscience
Morphological and functional types of neurons in cat ventral posterior thalamic nucleus
CT Yen, M Conley and EG Jones
Neurons in the thalamic ventral posterior (VB) nucleus of the cat were
investigated by extracellular and intracellular recording and by anatomical
methods involving either the retrograde transport of horseradish peroxidase
(HRP) or the intracellular injection of HRP. Two morphological types of
neurons could be detected by retrograde labeling from small injections of
HRP in the internal capsule adjacent to VB. These two and one other type,
judged to be an interneuron, could also be identified by intracellular
staining. Type I cells are large, have thick proximal dendrites which
branch in a tuft-like manner, and thick, rapidly conducting axons. They
possess few or no dendritic appendages. Type II cells are smaller and have
slender proximal dendrites which branch dichotomously and thin, slower
conducting axons. Those injected intracellularly are covered in fine,
hair-like dendritic appendages. Type III cells are small and have thin
processes that give rise to many bulbous dilatations and no obvious axon.
Type I and type II cells give off slender axon collaterals in the thalamic
reticular nucleus but not in VB. Examples of both types of cell could be
antidromically activated from the somatic sensory cortex. Type I and type
II cells recovered histologically after intracellular recording included
examples of most types of receptive field, including several forms of
cutaneous and deep fields, as classified by us in a parallel intra- and
extracellular study of unit responses. All but one type I cell, however,
responded in a transient manner to peripheral stimulation. The remaining
type I cell and all members of an admittedly small sample of type II cells
responded in a sustained manner. The sample of recovered interneurons and
of units that could not be driven antidromically from the cerebral cortex
suggested that they, too, included all receptive field types. We conclude
that submodality specificity in VB is not represented by morphological
specificity in thalamocortical relay cells or interneurons. Some other
functional parameter, such as tonic or phasic responsiveness, may be more
obviously correlated with relay cell morphology.
Previous Article | Next Article
