CENTRAL COMPLEX OF THE PRIMATE THALAMUS - A QUANTITATIVE-ANALYSIS OF NEURONAL MORPHOLOGY

Neuronal morphology was analyzed in the central complex (centre median -parafascicular complex) of macaques and humans. Cell bodies were desc ribed from Nissl material. Golgi-impregnated dendritic arborizations w ere reconstructed from serial sections and digitized in three dimensio ns by computer-assisted microscopy. The central complex was subdivided into three parts on the basis of cytoarchitectonic and hodological cr iteria: pars parafascicularis (medial), pars media (intermediate), and pars paralateralis (lateral). The mean cross-sectional areas of cell bodies were identical (181 mum2) in the three parts in macaques. In hu mans they were larger in the pars parafascicularis (304 mum2) than in the other parts (248 and 240 mum2). Small local circuit neurons were f ound throughout the complex. Large projection neurons differed statist ically in the three parts. In macaques, pars parafascicularis neurons had few dendritic stems and tips (3-11) and a short total dendritic le ngth (2,000 mum). Pars paralateralis neurons had more ramified (5-60) and longer (5,800 mum) dendrites. They bore numerous axonlike processe s. Pars media neurons had intermediate characteristics (5-9; 2,400 mum ). In humans, pars parafascicular neurons had similar topological char acteristics (3-12) but longer dendrites (3,000 mum) than in the monkey . Pars paralateralis neurons had more branched (6-71) and longer (9,00 0 mum) dendrites, with more numerous axonlike processes. Pars media ne urons also had intermediate characteristics (4-25; 3,800 mum). The pre sent study supports a tripartite subdivision of the primate central co mplex and demonstrates significant interspecies differences. (C) 1994 Wiley-Liss, Inc.