Nociceptive induced activation of exploratory behaviour: a role for ß-endorphin

Examined the role of β-endorphin in the regulation of open-field behavior in 19 male rabbits during the formalin test. Sham-injected Ss showed no pain reactions. Formalin-injected Ss displayed short-lived reactions that appeared immediately after injection, gradually decreased during Trial 2 (1 wk after Trial 1 immediately after β-endorphin treatment), and never recurred in Trial 3 (10 min after treatment). Formalin increased locomotor activity and rearing, but this effect did not occur in anti-β-endorphin-treated Ss. Results suggest that moderate, short-lasting pain induces the release of β-endorphin, which in turn activates locomotor activity and rearing. The β-endorphin system seems to be crucial in facilitating behavioral coping mechanisms and in improving response pattern