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Seth I. Rosenberg, MD; Leslie T. Malmgren, PhD; Peak Woo, MD

Arch Otolaryngol Head Neck Surg. 1989;115(1):78-86.

Abstract
• This investigation was initiated to provide data on the ultrastructural basis for neurologic age-related changes in laryngeal sensory function. In the present study, an animal model (female Wistar rats: age range: young [Y], 3 to 5 months; old [0], 25 months; and very old [VO], 29 to 30 months) was used to examine systematically changes in the internal branch of the superior laryngeal nerve with age using electron microscopic morphometric techniques. Total fiber counts, fiber populations (size categories), and mean fiber size for myelinated and unmyelinated fibers did not change with age. Qualitative changes were consistent with segmental demyelination and axonal degeneration in the older animals. There was also a significant age-related increase in the volume fraction of adaxonal Schwann cell cytoplasm (Y, 0.019; 0, 0.041; and VO, 0.042). Ultrastructural correlates of intracellular support and axonal transport showed a significant decrease in the numerical density of neurofilaments (Y, 0.126/µm²; O, 0.073/µm²; and VO, 0.078/µm²) in the older animals, but no change in the numerical density of microtubules. Energy metabolism correlates in the form of mitochondrial volume fraction did not change with age. There was a significant increase in the volume fraction of the intrafascicular extracellular space (Y, 0.224; O, 0.271; and VO, 0.301), indicating a late, age-related change in the extracellular environment. These changes could lead to decreased conduction velocity or complete fiber dysfunction. A number of these changes resembled those of aged human peripheral nerves already examined.

(Arch Otolaryngol Head Neck Surg 1989;115:78-86)

Author Affiliations
From the Department of Otolaryngology and Communication Sciences, Head and Neck Morphology Laboratory, State University of New York Health Science Center at Syracuse (Drs Rosenberg, Malmgren, and Woo) and the Veterans Administration Medical Center, Syracuse, NY (Dr Woo).

Footnotes
Accepted for publication Aug 15, 1988.

Reprint requests to Department of Otolaryngology, State University of New York Health Science Center, 750 E Adams St, 156 Weiskotten Hall, Syracuse, NY 13210 (Dr Malmgren).

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ABSTRACT