• Sankaranarayanan Kaliappan, Donald A Simone, and Ratan K Banik.
• NJ Neuroscience Institute and Seton Hall University School of Graduate Medical Education, JFK Medical Center, Edison, New Jersey.
• J Pain. 2018 Sep 1; 19 (9): 1015-1023.

AbstractThe under-reporting of pain and atypical manifestations of painful syndromes within the elderly population have been well documented, however, the specific relationship between pain and aging remains ambiguous. Previous studies have reported degenerative changes in primary afferents with aging. In this study, we questioned whether there is any change in the density of primary afferent endings within the epidermis of aged animals. Rats were categorically assessed in 4 age groups, each representing a key developmental stage across their life span: juvenile (2 months), adult (7 months); aged (18 months), and senescent (24-26 months). The plantar hind paw skin was removed, post-fixed, cut, and immunostained for protein gene product 9.5 and type IV collagen. Rats in the adult aged groups had significantly increased epidermal nerve densities and total lengths of immunoreactive nerve fibers, compared with juvenile as well as senescent rats. However, the paw withdrawal thresholds to punctate mechanical stimulation progressively increased with age, and did not exhibit a clear relationship with epidermal innervation. We conclude a nonlinear, inverted-U shaped relationship between rat plantar epidermal nerve density with aging, which does not correlate with mechanically-induced paw withdrawal behaviors.Copyright © 2018 The American Pain Society. Published by Elsevier Inc. All rights reserved.

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