[Stress-induced analgesia (author's transl)]

Area of Science:

• Neuroscience
• Psychology
• Pain Research

Background:

• Stress, particularly the expectation of severe pain, can modulate physiological responses.
• The nociceptive flexion reflex of the lower limb (RIII, Bi) is a measurable indicator of pain processing.
• Endogenous opiate systems are known to play a role in pain modulation.

Purpose of the Study:

• To investigate the impact of repetitive stress (expectation of severe pain) on the human nociceptive flexion reflex threshold.
• To determine the role of endogenous opiates in stress-induced changes in pain perception.
• To compare human responses to animal models of stress and pain.

Main Methods:

• Normal subjects were exposed to repetitive stress involving the expectation of severe pain over 60-90 minutes.
• The threshold of the nociceptive flexion reflex of the lower limb (RIII, Bi) was measured.
• Naloxone (an opioid antagonist) or a placebo was administered in a double-blind manner.

Main Results:

• Repetitive stress led to a progressive and significant increase in the RIII, Bi reflex threshold.
• Naloxone administration completely reversed the stress-induced increase in the reflex threshold, lowering it below baseline.
• Placebo administration had no significant effect on the reflex threshold compared to control values.

Conclusions:

• Endogenous opiate systems are involved in the human stress response.
• Stress can activate the body's natural pain-dampening mechanisms.
• These findings in humans align with previous observations in animal studies, supporting a conserved role for endogenous opiates in stress.