Effect of Age on the Structure of Meissner Corpuscles in Forepad Digital Pads of Mice
Meissner corpuscles in forepaw digital pads of albino mice were examined by light and electron microscopy to determine structural age-changes. After 1.5 months of age, no intraepidermal nerve fibers were seen extending from corpuscles. From young (1.5-6 months) to middle age (9-15 months), corpuscles became larger and more complex, gaining more horizontally arranged terminals, associated lamellae and connective tissue. At old age (18-26 months), corpuscles became small and lobulated, appearing disorganized. There was no loosening of the corpuscle-epidermal interface. An increase in collagenous connective tissue and basal lamina duplication occurred with advancing age. Ultrastructural age-changes consisted of disorganization of the axonal organelles, rounding of the axon profiles with loss of axonal processes, regression of the perineural capsular epithelium, attenuation and loss of lamellae, loss of caveoli, mitochondrial degeneration and lipofuscin accumulation. Intraepidermal terminals were thought to be present only during the period of corpuscle development which extends only to include age 1.5 months. Corpuscle growth and maturation until middle age possibly indicated sensitivity compensation for loss of corpuscles and innervating axons. At old age, the disruption of corpuscle structure, especially with loss of axonal processes and horizontal arrangement of terminals, likely dampened the sensitivity of Meissner corpuscles, and raised their threshold to stimuli, perhaps making them nonfunctional. An increase in collagenous connective tissue was thought to have a significant effect on the physical transmission of pressure waves to the transducer. The significance of mitochondrial degeneration and lipofuscin accumulation was considered. Atrophic corpuscles seen in abundance by old age probably occurred as a consequence of age-changes in axonal transport promoting distal axonopathy.
Anatomy, Animal Experimentation and Research, Nervous System, Neuroscience and Neurobiology, Nerve Endings -- growth & development; Mice -- growth & development; Age Factors
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