Central complex of the primate thalamus: A quantitative analysis of neuronal morphology

Abstract

Neuronal morphology was analyzed in the central complex (centre median-parafascicular complex) of macaques and humans. Cell bodies were described from Nissl material. Golgi-impregnated dendritic arborizations were reconstructed from serial sections and digitized in three dimensions by computer-assisted microscopy. The central complex was subdivided into three parts on the basis of cytoarchitectonic and hodological criteria: pars parafascicularis (medial), pars media (intermediate), and pars paralateralis (lateral). The mean cross-sectional areas of cell bodies were identical (181 microns2) in the three parts in macaques. In humans they were larger in the pars parafascicularis (304 microns2) than in the other parts (248 and 240 microns2). Small local circuit neurons were found throughout the complex. Large projection neurons differed statistically in the three parts. In macaques, pars parafascicularis neurons had few dendritic stems and tips (3-11) and a short total dendritic length (2,000 microns). Pars paralateralis neurons had more ramified (5-60) and longer (5,800 microns) dendrites. They bore numerous axonlike processes. Pars media neurons had intermediate characteristics (5-19; 2,400 microns). In humans, pars parafascicular neurons had similar topological characteristics (3-12) but longer dendrites (3,000 microns) than in the monkey. Pars paralateralis neurons had more branched (6-71) and longer (9,000 microns) dendrites, with more numerous axonlike processes. Pars media neurons also had intermediate characteristics (4-25; 3,800 microns). The present study supports a tripartite subdivision of the primate central complex and demonstrates significant interspecies differences.

Postnatal maturational properties of rat parafascicular thalamic neurons recorded in vitro

“…The morphology of the biocytin-labeled Pf cells sampled in this study matched that previously reported for Pf cells in rodents and other species using various single cell labeling techniques (Hazlett et al, 1976;Sugiyama et al, 1992b;Fenelon et al, 1994;Deschenes et al, 1995;Deschenes et al, 1996;Vercelli et al, 2003;Parent and Parent, 2005). Specifically, Pf cells exhibited long, unramifying primary dendrites unlike the compact, bushy dendritic trees which characterize neighboring thalamic relay neurons in the rat (Harris, 1986;Sawyer et al, 1989;Bartlett and Smith, 1999;Li et al, 2003).…”

Single-axon tracing and three-dimensional reconstruction of centre médian-parafascicular thalamic neurons in primates

“…The exact role of these peculiar dendritic appendages is unknown, but they could markedly enhance the integrative capacity of intralaminar thalamic neurons. That the morphological traits of injected CM/Pf neurons correspond to those reported in Golgi studies of primate CM/Pf complex (Hazlett et al, 1976;Fénelon et al, 1994) validates the present injection approach as a means to investigate the somatodendritic domain of single projection neurons.…”

Morphology of thalamocortical neurons projecting to the primary somatosensory cortex and their relationship to spinothalamic terminals in the squirrel monkey

“…CL and CM neurons can respond to noxious and other sensory stimuli (Dong et al, 1978;Dostrovsky and Guilbaud, 1990). Recently, Fenelon et al (1994) have studied the neuronal morphology in the central complex (CM and Pf in our terminology) of both macaque monkey and human thalami by means of the Golgi method. These researchers classified the central complex into three subdivisions, and indicated that the large, principal neurons in the different subdivisions were different in their dendritic domains.…”