QUANTITATIVE-ANALYSES OF INTRACELLULARLY CHARACTERIZED AND LABELED THALAMOCORTICAL PROJECTION NEURONS IN THE VENTROBASAL COMPLEX OF PRIMATES

This study describes the architecture of neurons and individual dendri tic arbors of thirteen intracellularly labeled thalamocortical project ion neurons that respond to non-noxious stimuli from the primate (Maca ca fascicularis or Macaca mulatta) ventrobasal complex (VB). The neuro ns compose a homogeneous morphological class with total dendritic leng ths from 10,169 mum to 21,711 mum (mean 17,615 mum +/- 3,705). The lab eled neurons were remarkably similar in most measured parameters inclu ding the number of dendrites (7.5 +/- 1.2), percentage of dichotomous branching (89.8% +/- 3.4), and contribution of terminal branches to to tal dendritic length (88.4% +/- 2.0). The individual dendrites ranged in total length from 443 mum to 7,657 mum with a mean of 2,346 mum (+/ - 137, n = 98). There was a positive correlation between stem dendrite diameter and total dendrite length, making it possible to estimate th e total size of an individual dendrite by measuring the stem dendrite diameter. There was only a small increase in mean path distance with i ncreasing dendritic size at the whole neuron and individual dendritic levels, so that for individual dendrites the mean path distance of a d endrite consisting of only two segments was 199 mum, while the mean pa th distance for a dendrite with eight segments was only 45 mum longer. Analysis of dendrite diameter, segment order, and path distance shows that dendritic diameter is not reliable for determining the location of synaptic contacts viewed by electron microscopy onto dendritic tree s. The small variation of measured parameters between these neurons pr esents a powerful tool for future developmental, plasticity and compar ative studies of VB neurons. (C) 1993 Wiley-Liss, Inc.