Distinctive implication of emotional factors in various types of stress-induced analgesia.

Diazepam, an antianxietic agent, antagonized the stress-induced analgesia (SIA) distinctively depending on the characteristics of the stress. Psychological (PSY, using communication box)-SIA was completely blocked by 1 or 2 mg/kg of diazepam in the tail pinch (TP) method, but not antagonized by 1 mg/kg of the drug in the tail flick test. Swimming-SIA was resistant to diazepam in both methods and footshock-SIA was only suppressed slightly by 2 mg/kg in the TP method. Thus, emotional factors play an essential role in the production of PSY-SIA, although the participation of the factors in the other SIAs can not be excluded.