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Age‐related loss of knee joint afferents in mice
Author(s) -
Salo P. T.,
Tatton W. G.
Publication year - 1993
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490350609
Subject(s) - anatomy , lumbar , life span , population , ganglion , knee joint , dorsal root ganglion , biology , monoaminergic , medicine , dorsum , surgery , serotonin , receptor , environmental health , evolutionary biology
Previous work in our laboratory revealed markedly different rates of age‐related death of four monoaminergic neuronal populations in the C57BL/6 mouse. Although dorsal root ganglion neurons (DRGns) have been reported not to suffer similar age‐related death in rodents, we determined if there is age‐related death of the subpopulation of DRGns innervating the knee joints of C57BL/6 mice, which are known to develop degenerative arthritis with aging. The somata of dorsal root ganglion neurons innervating the mouse knee joint (KJ‐DRGns) were identified by retrograde tracing with Fluoro‐Gold (FG). Lumbar ganglia were serially sectioned and the numbers of FG‐labelled KJ‐DRGns counted at five ages encompassing the animal's life span. Changes in size of the total population of lumbar DRGns (L‐DRGns) were estimated by counting nucleated somata from every fifth toluidine blue‐stained serial section from the L3 and L4 lumbar ganglia at three different ages. Using a computer‐assisted video morphometric technique somal areas were measured from random sections to determine the distribution of sizes of neurons in the KJ‐DRGn and general lumbar DRGn populations at different ages. Counts of FG‐labelled joint afferents were 238.5 ± 80.3 (mean SD) KJ‐DRGns per knee at 2 months of age, declining to 103.2 ± 20.1 by 24 months, representing a 57% loss over the average life span of the C57 mice. The loss occurred in two phases, with a rapid rate over the first 8 months of life and a more moderate rate of loss over the remaining months. L‐DRGn numbers revealed a slower overall rate of loss in comparison to the KJ‐DRGn population with an average 33.7% loss over the life span of this mouse. Somal size measurements revealed that the larger sizes of KJ‐DRGns were lost over the first 8 months of life, with little change in the distribution of somal sizes thereafter. The distributions of sizes of the L‐DRGn population did not change significantly over the life spans of the mice. The data provides evidence that the age‐related loss of KJ‐DRGns is significantly greater than DRGns in general, and may be particularly apparent in the population of largersized presumed mechanoreceptor neurons. The loss of the KJ‐DRGns is approximately reciprocal to the incidence rate of knee joint osteoarthritis reported for the C57BL/6 mice. © 1993 Wiley‐Liss, Inc.