Effects of extremely low frequency magnetic fields on pain thresholds in mice: roles of melatonin and opioids.

Abstract

1. We studied the effects of extremely low frequency (ELF, 60 Hz) magnetic fields (MFs) on pain thresholds using the hot plate test. The implication of opioid and benzodiazepine system in the MFs-induced alteration of pain thresholds was also studied. 2. There was an increase at night time and a decrease at daytime of pain thresholds in normal mice. Exposure of MFs (24 h, 20 gauss (G)) inhibited the increase of pain thresholds at night time and even produced hyperalgesia at daytime. 3. The increase of pain thresholds induced by melatonin at daytime was inhibited by exposure to MFs (24 h, 20 G) or opioid antagonist naloxone. The MFs and naloxone synergically inhibited hypoalgesia produced by melatonin. The hyperalgesia at daytime after MFs exposure was potentiated by the benzodiazepine agonist, diazepam, and inhibited by the benzodiazepine antagonist, flumazenil. There was no significant difference in all rotarod performance we tested. 4. From these results, it is suggested that exposure to MFs inhibits the increase of pain thresholds at night time and produces hyperalgesia at daytime with the involvement of opioid and benzodiazepine systems.

AI evidence extraction

Main findings

In normal mice, pain thresholds increased at night and decreased during daytime. Exposure to a 60 Hz magnetic field (20 G) for 24 h inhibited the nighttime increase in pain thresholds and produced hyperalgesia during daytime. Melatonin-induced increases in pain thresholds during daytime were inhibited by magnetic-field exposure or by naloxone, with magnetic-field exposure and naloxone showing synergic inhibition; daytime hyperalgesia after magnetic-field exposure was potentiated by diazepam and inhibited by flumazenil, while rotarod performance showed no significant differences.

Outcomes measured

• Pain thresholds (hot plate test)
• Hot plate hyperalgesia/hypoalgesia patterns (day vs night)
• Effects/modulation by melatonin
• Effects/modulation by naloxone (opioid antagonist)
• Effects/modulation by diazepam (benzodiazepine agonist)
• Effects/modulation by flumazenil (benzodiazepine antagonist)
• Motor performance (rotarod)

Limitations

• Sample size not reported in abstract
• Exposure source/setup details not described beyond frequency, intensity, and duration
• Animal study; generalizability to humans not addressed in abstract
• Mechanistic conclusions (opioid/benzodiazepine involvement) are based on pharmacologic modulation as described in the abstract

Suggested hubs

• animal-studies (0.9)
  Experimental study in mice assessing ELF magnetic-field effects on pain thresholds.

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    "study_type": "animal",
    "exposure": {
        "band": "ELF",
        "source": null,
        "frequency_mhz": 6.00000000000000015200514458246772164784488268196582794189453125e-5,
        "sar_wkg": null,
        "duration": "24 h"
    },
    "population": "Mice",
    "sample_size": null,
    "outcomes": [
        "Pain thresholds (hot plate test)",
        "Hot plate hyperalgesia/hypoalgesia patterns (day vs night)",
        "Effects/modulation by melatonin",
        "Effects/modulation by naloxone (opioid antagonist)",
        "Effects/modulation by diazepam (benzodiazepine agonist)",
        "Effects/modulation by flumazenil (benzodiazepine antagonist)",
        "Motor performance (rotarod)"
    ],
    "main_findings": "In normal mice, pain thresholds increased at night and decreased during daytime. Exposure to a 60 Hz magnetic field (20 G) for 24 h inhibited the nighttime increase in pain thresholds and produced hyperalgesia during daytime. Melatonin-induced increases in pain thresholds during daytime were inhibited by magnetic-field exposure or by naloxone, with magnetic-field exposure and naloxone showing synergic inhibition; daytime hyperalgesia after magnetic-field exposure was potentiated by diazepam and inhibited by flumazenil, while rotarod performance showed no significant differences.",
    "effect_direction": "harm",
    "limitations": [
        "Sample size not reported in abstract",
        "Exposure source/setup details not described beyond frequency, intensity, and duration",
        "Animal study; generalizability to humans not addressed in abstract",
        "Mechanistic conclusions (opioid/benzodiazepine involvement) are based on pharmacologic modulation as described in the abstract"
    ],
    "evidence_strength": "low",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "extremely low frequency",
        "ELF",
        "magnetic fields",
        "60 Hz",
        "20 gauss",
        "pain threshold",
        "hot plate test",
        "hyperalgesia",
        "melatonin",
        "opioids",
        "naloxone",
        "benzodiazepines",
        "diazepam",
        "flumazenil",
        "mice"
    ],
    "suggested_hubs": [
        {
            "slug": "animal-studies",
            "weight": 0.90000000000000002220446049250313080847263336181640625,
            "reason": "Experimental study in mice assessing ELF magnetic-field effects on pain thresholds."
        }
    ]
}

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