Effect of age on the structure of Meissner corpuscles in murine digital pads

A light and electron microscopic study was performed to determine age changes in Meissner corpuscles. In forepaw digital pads of mice aged to their maximum life expectancy, corpuscles were found to increase in size and complexity until middle age, and then to become smaller, disorganized and lobulated with more advanced age. Nerve terminals at more advanced ages became attenuated with a loss of axonal processes, increased density of the axoplasm, and disordered arrangement of the organelles. Degeneration of axonal mitochondria accelerated with age. Lamellar cell processes investing the axons often become dense and attenuated with fewer plasmalemma-associated vesicles. Basal laminae remained where lamellar processes had disintegrated. Lipofuscin was seen in the lamellar cells only at extremely old age. Extracellular material composed of fine basal lamina substance and collagen fibrils increased remarkably with age. Increased growth and complexity of corpuscles until middle age perhaps compensated for age-associated loss of corpuscles and primary sensory neurons. Changes predominating at older ages are attributed to distal axonopathy and atrophy of the sensory neurons. The probable effect of these age changes on cutaneous sensitivity is considered in relation to current theory of mechanoelectric transduction.