Comparison of cortically and subcortically controlled motor systems: I. Morphology of intracellularly filled rubrospinal neurons in rat and turtle.
The rat and turtle differ markedly in major structural features of the corticocerebellorubrospinal circuitry. Although both species have a well-developed cerebellorubrospinal system, they differ in that a direct cerebral cortical input to the red nucleus is present only in the rat. The aim of the present study was to compare features of the soma and dendritic morphology of rubrospinal neurons that receive cortical input, as in rats, with those that do not, as in turtles. Intracellular Lucifer Yellow injections of neurons retrogradely labeled with Fast Blue in the rat or activity-dependent sulforhodamine-labeled neurons in the turtle were used to fill rubrospinal neurons in 150-200-microm-thick fixed sections. Images of filled neurons were imported into a computer to analyze quantitatively soma and dendritic morphology. The results show that rubrospinal soma size is slightly larger in the rat than in the turtle. However, analysis of the dendritic morphology, including total dendritic length, length of primary, secondary, and tertiary dendritic branches, and a Scholl analysis of dendritic branch intersections across concentric rings, demonstrated no significant differences between the two species. These findings suggest that the basic dendritic morphology of rubrospinal neurons may have been established early in phylogeny, preceding the evolution of cortical inputs. Alternatively, similar dendritic morphologies may have arisen due to the presence of other synapses in the turtle that occupy the sites of the cortical input in the rat. This comparative approach provides insights into the information processing capabilities of cortically versus subcortically controlled motor systems.
Lustig
D G
DG
Department of Anatomy & Structural Biology, University of South Dakota School of Medicine, Vermillion 57069, USA.
Herrick
J L
JL
Keifer
J
J
D000818:Animals; D003712:Dendrites / Q000648:ultrastructure; D005456:Fluorescent Dyes; D007091:Image Processing, Computer-Assisted; D007546:Isoquinolines; D009044:Motor Cortex / Q000166:cytology*; D009474:Neurons / Q000648:ultrastructure*; D051381:Rats; D017207:Rats, Sprague-Dawley / Q000033:anatomy & histology*; D012012:Red Nucleus / Q000166:cytology*; D013045:Species Specificity; D013116:Spinal Cord / Q000166:cytology*; D014426:Turtles / Q000033:anatomy & histology*
D005456:Fluorescent Dyes; D007546:Isoquinolines; C017475:lucifer yellow