Altered neuron population in L7 segment of dogs with experimental hind-limb rigidity

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Abstract
Establishment of the total neuronal population in a single spinal segment, its distribution in the spinal gray matter, cellular-caliber spectra, and motoneuron:interneuron ratio, hitherto unavailable, has made it possible to correlate quantitatively the functional disorganization in the lumbosacral cord of dogs with hind-limb rigidity, produced by temporary ischemia, with the neuronal deficit and with previously established neurophysiological alterations. There are some 375,000 neurons in the L7 segment: one-half in the dorsal horn and one-fourth each in intermediate zone and ventral horns. Small cells outnumber large ones 24:1. Some 82% of the large neurons are in the ventral horn; two-thirds of these are alpha motoneurons. Mononeurons, large and small, are outnumbered by interneurons, 7:1 in the ventral horn and 30:1 in the entire spinal gray matter. Most or all of the cells destroyed in L7 segments of three rigid dogs were interneurons. All motoneurons may survive when 80% of the interneurons are destroyed. The survival percentage was consistently higher among the neurons in the ventral horn. The higher mortality among small neurons in ventral horns was due principally to topographical deployment.