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 comple x. One hundred nine dendrites from six ventral posterolateral (VPL) ne urons and six ventral posteromedial (VPM) neurons were examined. Measu rement of several parameters showed that the individual dendrites were very similar to each other in overall architecture even though they v aried greatly in total length and number of dendritic branches. The me an path distance (length from soma to a dendritic tip) was very simila r for all dendrites in each group (VPL or VPM) regardless of the numbe r of branches found along the path distance. However, VPL dendrites ha d a longer mean path distance (VPL = 206 +/- 36 mu m; n = 51) than VPM dendrites (VPM = 182 +/- 29 mu m; n = 58; P < 0.001). For all dendrit es there was a strong correlation between the stem dendrite diameter a nd the dendritic length, which allows the estimation of dendritic leng th from dendrite diameter. Analysis of dendritic sealing shows that br anches higher than first order do not follow Rall's 3/2 power rule, so these neurons cannot be modeled using the equivalent cylinder approxi mation. The data add to the qualitative descriptions of cat ventrobasa l (VB) TCP dendrites currently available and provide a basis for futur e comparative, developmental, and plasticity studies. Analysis shows t hat 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. (C ) 1995 Wiley-Liss, Inc.