The neurons in the centromedian‐parafascicular complex of the monkey (Macaca mulatta): A Golgi Study

Abstract

The neurons of the nucleus centrum medianum and the neurons of the nucleus parafascicularis were studied in Golgi preparations of the adult monkey (Macaca mulatta). The cell bodies of the prinicipal neurons in the nucleus centrum medianum have a few somatic spines and vary in shape: some are cubical with protruding angles; some are egg-shaped; some are elongated and sausage-shaped. Four to six slightly branched dendrites of unequal thickness radiate from the cell body. Some dendrites extend for nearly 500 microns; all have dendritic spines. In the nucleus parafascicularis there are two varieties of principal neurons: (1) neurons with somatic spines and (2) neurons without somatic spines. The neurons with somatic spines are most numerous. They have polygonal-shaped cell bodies, prominent somatic spines and processes, larger than spines but considerably smaller than dendrites. These processes bear spines and are designated here "microdendrites." Spines and occasionally a "microdendrite" are found on the axon-hillocks. Five to six dendrites of unequal thickness emerge from the cell bodies. Some extend for more than 500 microns; all have prominent dendritic spines. The neurons without somatic spines are relatively few. Usually three exceptionally long, slightly branched dendrites, one apical and two basal, emerge from their elongated, slim cell bodies. Some dendrites extend for more than 800 microns; all have few scattered spines. The Golgi type II neurons found in both of these intralaminar nuclei have small cell bodies and a few, relatively long, undulating dendrites, which bear bulbous dendritic appendages and beaded axon-like processes. Distally on these dendrites, where the appendages and processes are more numerous, the dendritic appendages and axon-like processes form complex entanglements. Distally on these dendrites, where the appendages and processes are more numerous, the dendritic appendages and axon-like processes form complex entanglements. Beaded axons are found on some but not all of the cell bodies. Morphologically these neurons resemble the local interneurons that have been described in various thalamic nuclei.

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).…”

“…In contrast, anatomical studies have long recognized that many cells in the Pf have a distinct morphology compared with thalamic relay nuclei (Hazlett et al, 1976;Hazlett and Hazlett, 1977;Pearson et al, 1984;Parent and Parent, 2005). Typically, they contain long unbranching processes in their proximal dendritic trees.…”

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.…”

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

“…In macaques, axons were not consistently identified on small neuron cell bodies (Hazlett et al, 1976). In some instances, beaded axons, structurally similar to the axonlike processes on dendrites, were seen emerging from the cell bodies (Hazlett et al, 1976). This raises the possibility that axonlike processes are equivalent to short axons in local circuit neurons, as previously suggested for small neurons of the substantia nigra (FranGois et al, 1979).…”

“…They gave rise to collaterals and arborized locally. In macaques, axons were not consistently identified on small neuron cell bodies (Hazlett et al, 1976). In some instances, beaded axons, structurally similar to the axonlike processes on dendrites, were seen emerging from the cell bodies (Hazlett et al, 1976).…”