PRESERVED FEATURES OF THALAMOCORTICAL PROJECTION NEURON DENDRITIC ARCHITECTURE IN THE SOMATOSENSORY THALAMUS OF THE RAT, CAT AND MACAQUE

A number of studies have shown that the organization of the mammalian somatosensory thalamus varies between species. As differences in cellu lar and synaptic thalamic organization would be expected to influence neuronal dendritic architecture, we compared somatosensory thalamocort ical projection (TCP) neurons from the rat, cat and macaque. The resul ts show that key features of the dendritic branching pattern remain un changed despite large differences in the size of TCP neurons between t he species. The features examined were: (i) ratio of the length of ter minal branches to the length of the entire dendritic tree; (ii) the pe rcentage of branch points that gave rise to two daughter branches as o pposed to those that gave rise to three or more daughter branches; (ii i) the proportional sum of absolute deviations (a measure of branching symmetry), and (iv) the mean branch order of the terminal segments. T he present study provides evidence that somatosensory TCP neurons in t hese species comprise a homogeneous class and share a common dendritic architecture that is conserved across species despite changes in othe r aspects of thalamic circuitry. This suggests that TCP neuronal form is based on relatively stable genetic blueprint and that epigenetic fa ctors (e.g. synaptic input) resulting from evolutionary changes in tha lamic organization have had less influence on dendritic architecture.