Swim Stress-induced Analgesia Research Articles

N-methyl- d-aspartic acid (NMDA) receptor antagonist MK-801 blocks non-opioid stress-induced analgesia. I. Comparison of opiate receptor-deficient and opiate receptor-rich strains of mice

The effects of the specific N-methyl- d-aspartic acid (NMDA) receptor antagonist MK-801 (0.075 mg/kg), and the specific opiate receptor antagonist naloxone (10 mg/kg), on swim stress-induced analgesia (SSIA) were studied in opiate receptor-deficient (CXBK) and opiate receptor-rich (CXBH) mice. Animals were subjected to forced swimming, and analgesia was assessed using the hot-plate test. In CXBK mice SSIA was blocked by MK-801 but was completely insensitive to naloxone. In CXBH mice SSIA was partially attenuated both by naloxone and MK-801, and it was nearly abolished by a combination of these drugs. Morphine analgesia (10 mg/kg) was abolished by naloxone but completely unaffected by MK-801 in CXBH mice. These findings suggest that the NMDA receptor is critically involved in the non-opioid component of SSIA.

Day-night rhythms of opioid and non-opioid stress-induced analgesia: differential inhibitory effects of exposure to magnetic fields

Day-night rhythms occurred in the naloxone-reversible (1.0 mg/kg), warm (opioid) and naloxone-insensitive, cold (non-opioid) swim stress-induced analgesia displayed by CF-1 mice. Maximum antinociceptive responses were evident at night, with the cold stress having significantly greater day- and night-time analgesic effects than the warm stress. An exposure for 30 min to a 0.5 Hz rotating magnetic field (1.5–90 gauss) reduced both the warm and cold stress-induced analgesia, with the magnetic stimuli having significantly greater inhibitory effects at night and on the opioid-induced responses. These results indicate that exposure to oscillating magnetic fields can significantly, and differentially, alter both opioid and non-opioid stress-induced analgesia and their day-night rhythms.

Magnetic fields and stress: Day-night differences

1. 1. An exposure for 30 min to a 0.5 Hz rotating magnetic field (1.5–90 G) significantly reduced warm water swim stress-induced opioid analgesia in CF-1 male mice. Pre-treatment with naloxone (1.0 mg/kg) had comparable inhibitory effects on warm water swim induced analgesia. 2. 2. The magnetic stimuli also eliminated the day-night rhythm in stress-induced analgesia, with maximum inhibitory effects occurring in the dark period when peak analgesia was present. 3. 3. These results indicate that magnetic stimuli can significantly alter day-night rhythms of stress-induced activation of endogenous opioid systems and their behavioral and physiological consequences. These elevated night time effects may involve actions on the pineal gland, while the day time actions may involve alterations in the distribution and transport of Ca ++ and or other divalent ions.