Alterations in activity at auditory nuclei of the rat induced by exposure to microwave radiation: autoradiographic evidence using [14C]2-deoxy-D-glucose.

Abstract

Autoradiographic maps of brain activity in rats exposed to pulsed or continuous-wave (CW) microwave radiation were made using [14C]2-deoxy-D-glucose ([14C]2-DG). Special emphasis was given to measurements of activity in the auditory system because previous work had shown that pulsed microwave radiation can elicit auditory responses in man and other animals. In particular, one middle ear was ablated in nine rats to attenuate the transmission of air-borne sound to one cochlea. The resulting imbalance in auditory input for four animals not exposed to microwave radiation was reflected as a bilateral asymmetry of [14C]2-DG uptake at the inferior colliculus and medial geniculate body. In contrast, a symmetrical pattern of uptake at these structures in an animal exposed to pulsed microwave radiation showed that this stimulus bypasses the middle ear in eliciting auditory responses. This result established the utility of the [14C]2-DG method for demonstrating a known effect of microwave radiation on brain activity. The results also revealed responses at auditory nuclei in 4 animals exposed to CW microwave radiation. These responses, which have not been observed with other methods, were evident at the power densities of 2.5 and 10 mW/sq. cm. To exclude the possibility that CW microwave radiation produced this result by direct action on brain tissue, additional data were obtained from two rats with one cochlea destroyed. In both animals, the uptake of [14C]2-DG at the inferior colliculus and medial geniculate body was virtually identical to the uptake in animals not exposed to microwave radiation, i.e. greatest on the side of the brain contralateral to the intact cochlea. This finding, coupled with the finding of a bilateral symmetry of [14C]2-DG uptake in the auditory pathways of animals with one middle ear ablated, confirmed the hypothesis that auditory responses to CW microwave radiation originate within the cochlea. Effects on brain activity outside of the auditory system were not found in qualitative analyses of autoradiographs for the conditions of exposure to CW microwave radiation noted above or for exposure to pulsed microwave radiation at the average power density of 2.5 mW/sq. cm.

AI evidence extraction

Main findings

Autoradiographic [14C]2-deoxy-D-glucose mapping showed that pulsed microwave exposure produced symmetrical uptake in auditory nuclei despite unilateral middle ear ablation, consistent with bypassing the middle ear in eliciting auditory responses. Four animals exposed to continuous-wave microwave radiation showed responses at auditory nuclei at power densities of 2.5 and 10 mW/sq cm. In two rats with one cochlea destroyed, uptake patterns during CW exposure resembled non-exposed animals, supporting a cochlear origin for CW microwave-induced auditory responses; no qualitative effects outside the auditory system were found under the stated exposure conditions.

Outcomes measured

• Brain activity measured by [14C]2-deoxy-D-glucose uptake
• Auditory nuclei activity (inferior colliculus, medial geniculate body)
• Auditory pathway symmetry/asymmetry with middle ear ablation or cochlea destruction

Limitations

• Sample size not fully reported in abstract (only some subgroup counts provided).
• Exposure parameters incomplete (frequency, modulation details, duration not stated).
• Some findings described qualitatively (e.g., effects outside auditory system) rather than with quantitative statistics in the abstract.
• Animal model; relevance to humans not established in abstract.

{
    "study_type": "animal",
    "exposure": {
        "band": "microwave",
        "source": null,
        "frequency_mhz": null,
        "sar_wkg": null,
        "duration": null
    },
    "population": "Rats",
    "sample_size": null,
    "outcomes": [
        "Brain activity measured by [14C]2-deoxy-D-glucose uptake",
        "Auditory nuclei activity (inferior colliculus, medial geniculate body)",
        "Auditory pathway symmetry/asymmetry with middle ear ablation or cochlea destruction"
    ],
    "main_findings": "Autoradiographic [14C]2-deoxy-D-glucose mapping showed that pulsed microwave exposure produced symmetrical uptake in auditory nuclei despite unilateral middle ear ablation, consistent with bypassing the middle ear in eliciting auditory responses. Four animals exposed to continuous-wave microwave radiation showed responses at auditory nuclei at power densities of 2.5 and 10 mW/sq cm. In two rats with one cochlea destroyed, uptake patterns during CW exposure resembled non-exposed animals, supporting a cochlear origin for CW microwave-induced auditory responses; no qualitative effects outside the auditory system were found under the stated exposure conditions.",
    "effect_direction": "harm",
    "limitations": [
        "Sample size not fully reported in abstract (only some subgroup counts provided).",
        "Exposure parameters incomplete (frequency, modulation details, duration not stated).",
        "Some findings described qualitatively (e.g., effects outside auditory system) rather than with quantitative statistics in the abstract.",
        "Animal model; relevance to humans not established in abstract."
    ],
    "evidence_strength": "low",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "microwave radiation",
        "pulsed",
        "continuous-wave",
        "rat",
        "auditory system",
        "inferior colliculus",
        "medial geniculate body",
        "[14C]2-deoxy-D-glucose",
        "autoradiography",
        "microwave auditory effect"
    ],
    "suggested_hubs": []
}

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