Effect of 2450 MHz microwave energy on the blood-brain barrier to hydrophilic molecules. A. Effect on the permeability to sodium fluorescein

Brain Res · 1984 · Mixed · Low evidence

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MixedLow evidencePaper 6677

Study snapshot

PublicationBrain Res · 1984

Study typeanimal

Reported directionMixed

Evidence ratingLow

Abstract

Significantly elevated levels of sodium fluorescein (MW 376) were found only in the brains of conscious rats made considerably hyperthermic (colonic temperatures greater than 41.0 degrees C) by exposure to ambient heat (42 +/- 2 degrees C) for 90 min or 2450 MHz CW microwave energy at 65 mW/cm2 (SAR approximately equal to 13.0 W/kg) for 30 or 90 min. For microwave-exposed rats, fluorescein levels within the cortex and hypothalamus appeared to increase with increasing duration of exposure. This trend was not apparent in the cerebellum or medulla. Exposure to ambient heat resulted in increased fluorescein with the cortex, hypothalamus and medulla, but not the cerebellum, and, in general, ambient heat was not as effective as microwave energy in raising tracer concentrations within the brain. By far the greatest elevation of fluorescein dye in the brain occurred in those animals whose blood-brain barrier had been opened osmotically by intracarotid injection of 10 M urea. It is suggested that increased levels of sodium fluorescein found in the brain tissue of ambient heat and microwave-exposed rats most likely represent technically derived artifact and not a breakdown of the blood-brain barrier.

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeanimal

Effect directionmixed

PopulationConscious rats

Sample sizeNot supplied

Exposuremicrowave · 2450 MHz · 13 W/kg · 30 or 90 min

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

Significantly elevated sodium fluorescein levels were found only in brains of conscious rats made considerably hyperthermic (colonic temperatures >41.0°C) by either ambient heat exposure for 90 min or 2450 MHz continuous-wave microwave exposure at 65 mW/cm2 (SAR ~13 W/kg) for 30 or 90 min. In microwave-exposed rats, fluorescein levels in cortex and hypothalamus appeared to increase with longer exposure duration, while this trend was not apparent in cerebellum or medulla. The authors suggest the increased fluorescein levels most likely represent technically derived artifact rather than blood-brain barrier breakdown.

Outcomes measured

Blood-brain barrier permeability to hydrophilic molecules
Brain levels of sodium fluorescein (MW 376) in cortex, hypothalamus, cerebellum, medulla
Hyperthermia (colonic temperature >41.0°C)

Limitations

Sample size not reported in provided abstract/metadata
Authors attribute observed increases to possible technical artifact rather than true BBB disruption
Findings observed only under considerable hyperthermia (>41°C), limiting generalizability to non-thermal exposures

View raw extracted JSON

{
  "study_type": "animal",
  "exposure": {
    "band": "microwave",
    "source": null,
    "frequency_mhz": 2450,
    "sar_wkg": 13,
    "duration": "30 or 90 min"
  },
  "population": "Conscious rats",
  "sample_size": null,
  "outcomes": [
    "Blood-brain barrier permeability to hydrophilic molecules",
    "Brain levels of sodium fluorescein (MW 376) in cortex, hypothalamus, cerebellum, medulla",
    "Hyperthermia (colonic temperature >41.0°C)"
  ],
  "main_findings": "Significantly elevated sodium fluorescein levels were found only in brains of conscious rats made considerably hyperthermic (colonic temperatures >41.0°C) by either ambient heat exposure for 90 min or 2450 MHz continuous-wave microwave exposure at 65 mW/cm2 (SAR ~13 W/kg) for 30 or 90 min. In microwave-exposed rats, fluorescein levels in cortex and hypothalamus appeared to increase with longer exposure duration, while this trend was not apparent in cerebellum or medulla. The authors suggest the increased fluorescein levels most likely represent technically derived artifact rather than blood-brain barrier breakdown.",
  "effect_direction": "mixed",
  "limitations": [
    "Sample size not reported in provided abstract/metadata",
    "Authors attribute observed increases to possible technical artifact rather than true BBB disruption",
    "Findings observed only under considerable hyperthermia (>41°C), limiting generalizability to non-thermal exposures"
  ],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "2450 MHz",
    "microwave",
    "continuous wave",
    "SAR",
    "hyperthermia",
    "blood-brain barrier",
    "sodium fluorescein",
    "rat",
    "brain permeability",
    "ambient heat",
    "osmotically opened BBB",
    "urea"
  ],
  "suggested_hubs": [
    {
      "slug": "who-icnirp",
      "weight": 0.2,
      "reason": "Animal study on microwave exposure and BBB permeability; potentially relevant to RF safety discussions, though no policy content is provided."
    }
  ]
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1016/0165-0173(84)90021-3
PubMed: 6733539

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