The Mechanisms of Pain Modulation by Environmental Enrichment

Abstract

Mice raised in enriched environments display a host of behavioral and physiological differences from mice raised in standard cage housing. Enriched mice show enhanced pain behaviors, as well as elevated levels of neurogenesis and altered hormonal responses to stress. Although the effects of enriched housing on pain behavior have been well described in the literature, no physiological mechanisms by which enriched environments alter pain behavior have been described. The current study aimed to explore two possible mechanisms by which enrichment could alter pain behavior. One plausible physiological mechanism explored was altered endorphin activity as a result of stress. In one 2x2 experiment, mice were raised in either enriched environments or standard housing, and were treated with either naloxone or saline. Naloxone's effect on opioid receptors allowed the relation between endorphins and pain behavior to be explored. Another plausible physiological mechanism explored was the effect of neurogenesis. In a 2x2 experiment, mice were raised in one of two housing conditions, and were treated with either MAM or saline. MAM's neurogenesis blocking effects allowed for the effects of neurogenesis on pain behavior to be explored. The significant finding of this study was an altered level of f3 endorphin sensitivity in enriched animals. The relation of our findings to pain behavior is discussed.