Stressors and pain sensitivity in CFW mice. Role of opioid peptides.

Effects of several environmental situations on pain threshold were studied in CFW male mice. Immobilization induced significant and naloxone reversible analgesia. Isolation produced analgesia which was partially reversed by naloxone. One minute swimming in + 4 degrees C or + 42 degrees C water increased naloxone reversible analgesia. Isolation produced analgesia which was partially reversed by naloxone. One minute swimming in 4 degrees C or + 42 degrees C water increased naloxone irreversible pain threshold. Other situations: drinking 2% NaCl solution, disturbance of light-dark cycle or social aggregation did not produce analgesia. The role of these situations as stress-inducers, as well as the role of endogenous opioid peptides in stress-induced analgesia, were discussed.