Anterior horn cells of the spinal cord of an experimental animal demonstrate cell body rounding, peripheral displacement of the nuclei and dispersion of Nissl substance to the periphery of the cells. The findings described most likely indicate:

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Anterior horn cells of the spinal cord of an experimental animal demonstrate cell body rounding, peripheral displacement of the nuclei and dispersion of Nissl substance to the periphery of the cells.  The findings described most likely indicate:

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Sometimes axons become severed due to trauma. Such injury causes specific changes in both the proximal and distal segments of the axon, as well as in the neuronal body. Wallerian degeneration occurs in the segment of axon that has lost connection with the cell body. It represents the degeneration of axon and myelin distal to a point of injury. First, swelling and irregularity are noted in the distal segment of the axon. Within a week the axon is destroyed and its fragments are digested by Schwann cells and macrophages. Similar degenerative changes occur in the segment of axon that lies proximal to the injury. Degeneration of the proximal segment extends to the closest node of Ranvier. The changes seen in the neuronal body after the axon is severed are called axonal reaction. The cell body shows signs of cellular edema. It becomes swollen and rounded, with the nucleus displaced to the periphery. Nissl substance becomes fine, granular and dispersed throughout the cytoplasm (central chromatolysis). Axonal reaction becomes visible in 24-48 hours after the injury. Maximal changes in the neuronal body occur approximately 12 days after the injury. These changes reflect an increased synthesis of protein by the cells in order to regenerate the severed axon. (Choice A) Degenerative diseases are characterized by progressive loss of neurons with associated reactive glial changes. Neuronal loss in these conditions is selective: it affects one or more well-defined neuronal groups. Alzheimer's, Pick's, and Huntington's disease are all examples of degenerative disorders. (Choice B) Transient but profound hypoxia, ischemia or toxic injury may lead to the loss of neurons. Irreversible neuronal injury manifests with shrinkage of the neuronal body, deep eosinophilia of the cytoplasm, pyknosis of the nucleus and loss of Nissl substance. (Choice D) Compression atrophy may occur due to increased intracranial pressure or a mass lesion. A decrease in the size and number of neurons is characteristic of compression atrophy. (Choice E) Normal aging is characterized by atrophy and gradual neuronal loss. Axonal reaction is not associated with this process. Educational Objective: The changes in the body of a neuron after the axon has been severed are called axonal reaction. This process reflects an increased protein synthesis that facilitates axon repair. Enlarged, rounded cells with peripherally located nuclei and dispersed finely granular Nissl substance are seen.

Anterior Horn Cells of the Spinal Cord of an Experimental