Deafferentation effects in lateral cuneate nucleus of the cat: Correlation of structural alterations with firing pattern changes

The hypothesis that collateral sprouting might be correlated with recovery of function was tested by a combination of behavioral and anatomical studies. Partial hemisections, sparing the dorsal columns, were made between T l r and L1 of cat spinal cord. Initially, all reflex and locomotor hindlimb activity was depressed ipsilaterally. During two postoperative weeks behavioral and electromyographic responses increased in response to intrinsic reflex elicitation but not to descending or crossed reflex elicitation. Marked improvement in use of the limb occurred as intrinsic reflex activity increased and became, in some cases, hyperactive. The status then remained stable for ten months. Since intrinsic reflexes are mediated by ipsilateral dorsal roots, the intraspinal distribution of L5 or L,; dorsal roots was determined by degeneration methods ten months after hemisection or by quantitative radioautography 20 days after hemisection. By both methods, the dorsal root distribution was found to be asymmetrical in the spinal gray. It was greater on the experimental side and the distribution was altered, having a greater distribution medially in Rexed's lamina VI and laterally in lamina VII. These anatomical changes are considered as signs of collateral sprouting from dorsal roots in response to degeneration of descending tracts on the same side. Dorsal root distribution to dorsal horn (laminae I-IV), motor nuclei, and nucleus gracilis is symmetrical. Regions of increased and of expanded dorsal root input can be correlated with electrophysiologically determined location of interneurons in the path of cutaneous reflexes and of stretch reflex facilitation. Behavioral and anatomical changes were selective; intrinsic reflexes recovered or became hyperactive and ipsilateral dorsal roots showed evidence of collateral sprouting during the recovery period, although a causal relationship between the two cannot be proven, by the present experiments.

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Electron microscopic observations of nodes of ranvier in the external cuneate nucleus

Rosenstein

Leure-Dupree

1976

J of Comparative Neurology

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During the course of an investigation of the synaptic organization of the external cuneate nucleus (ECN) in the Sprague-Dawley albino rat, the ultrastructural morphology of nodes of Ranvier in the neuropil has been studied. The majority of nodes observed have the basic morphological features of conventional central nodes but there is individual variation with regard to length, surface area and cytoplasmic organelles. In addition, nodes with multiple myelinated branches are observed. Some nodes of Ranvier were observed to form specialized synaptic boutons. Two types of nodal synaptic boutons were present; a simple type and a complex type. Simple nodal boutons were observed more frequently. These nodes usually synapse upon a single dendritic element; the portion of the node opposite the presynaptic area has a morphology similar to conventional nodes. Complex nodal boutons are of greater dimension than simple nodal boutons and are usually in contact with several neuronal elements. They may be presynaptic to dendritic shafts or spines and are occasionally observed to be postsynaptic to small axonic profiles, a synaptic relationship which, until this report, has not been demonstrated in the central nervous system (CNS). The possible functional significance of these observations is discussed.

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Deafferentation effects in lateral cuneate nucleus of the cat: Correlation of structural alterations with firing pattern changes

Cited by 51 publications

References 20 publications

Signs of Plasticity and Reconnection in Spinal Cord Damage

Signs of Plasticity and Reconnection in Spinal Cord Damage

Restitution of function and collateral sprouting in the cat spinal cord: The partially hemisected animal

Electron microscopic observations of nodes of ranvier in the external cuneate nucleus

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