The Effect of Environmental Enrichment on Pain Behavior: Possible Mechanisms

Abstract

Environmental enrichment—characterized by increased social interaction, exploratory behavior, and physical activity—has been shown to increase hippocampal neurogenesis as well as the physiological response to stress, both of which cause various behavioral changes in mice. The purpose of the current study was to determine the physiological correlate of a third behavioral change following enrichment: altered pain behavior. Male and female mice were housed in enriched or standard conditions and treated with saline, MAM (a neurogenesis blocker), or naloxone (an opioid receptor antagonist) to explore two possible mechanisms: increased neurogenesis, and chronically elevated levels of β-endorphins—endogenous opioids—as a result of HPA-axis stimulation. Results from our study suggest that, while environmental enrichment was unable to consistently alter pain behavior, sex-dependent chronic elevations of β-endorphins might decrease the sensitivity of enriched males to the analgesic effects of opioid administration.