[Endogenous opioid mechanisms in the regulation of pain sensitivity and behavioral reactivity in various aversive states].

Study of the effect of naloxone that blocks opiate receptors on changes in thresholds of vocalization and latent periods of motile reaction in freely-behaving rats, at leg injury, intraperitoneal introduction of algogene, and at immobilization stress allowed to estimate the involvement of endogenous opiates in regulation of pain sensitivity and motile activity. Naloxone-weakened inhibition of vocalization is accompanied by the increase in inhibition of motile responses, characteristic for visceral pain and the absence of changes at trauma and immobilization stress suggest that opiates are involved in formation of endogenous analgesia at strong visceral pain stimulation.