Architecture of individual dendrites from intracellularly labeled thalamocortical projection neurons in the ventral posterolateral and ventral posteromedial nuclei of cat.

This study provides quantitative descriptions of individual dendrites from electrophysiologically characterized and intracellularly labeled thalamocortical projection (TCP) neurons of the cat ventrobasal complex. One hundred nine dendrites from six ventral posterolateral (VPL) neurons and six ventral posteromedial (VPM) neurons were examined. Measurement of several parameters showed that the individual dendrites were very similar to each other in overall architecture even though they varied greatly in total length and number of dendritic branches. The mean path distance (length from soma to a dendritic tip) was very similar for all dendrites in each group (VPL or VPM) regardless of the number of branches found along the path distance. However, VPL dendrites had a longer mean path distance (VPL = 206 +/- 36 microns; n = 51) than VPM dendrites (VPM = 182 +/- 29 microns; n = 58; P < 0.001). For all dendrites there was a strong correlation between the stem dendrite diameter and the dendritic length, which allows the estimation of dendritic length from dendrite diameter. Analysis of dendritic scaling shows that branches higher than first order do not follow Rall's 3/2 power rule, so these neurons cannot be modeled using the equivalent cylinder approximation. The data add to the qualitative descriptions of cat ventrobasal (VB) TCP dendrites currently available and provide a basis for future comparative, developmental, and plasticity studies. Analysis shows that many parameters of cat VB TCP dendrites fall within a narrow range, suggesting that, regardless of differences in length or superficial appearance, these dendrites share a stable underlying architecture.