Age differences in nociception and pain behaviours in the rat

Much remains to be learned about the effects of ageing on pain. Studies of life-span changes in nociception and pain behaviours in the rat are equivoc al making it difficult to draw firm conclusions. This paper reviews the ava ilable data and finds that age differences in nociception may be dependent on the pain test employed. Specifically, reflexive responses to nociceptive stimuli do not change with age while there may be no change or a linear de crease with age on more highly organized tests of nociception. Interestingl y, age differences in pain behaviours on models of tissue injury and inflam mation may not be linear. It is shown that important changes that begin at midlife in neuroanatomy, neurochemistry and endogenous pain inhibition may be associated with alterations in pain sensitivity. Several testable hypoth eses which might encourage future research in this domain are developed thr oughout this paper. (C) 2000 Published by Elsevier Science Ltd.