Alterations in alpha-adrenergic and muscarinic cholinergic receptor binding in rat brain following nonionizing radiation.

Abstract

Microwave radiation produces hyperthermia. The mammalian thermoregulatory system defends against changes in temperature by mobilizing diverse control mechanisms. Neurotransmitters play a major role in eliciting thermoregulatory responses. The involvement of adrenergic and muscarinic cholinergic receptors was investigated in radiation-induced hyperthermia. Rats were subjected to radiation at 700 MHz frequency and 15 mW/cm2 power density and the body temperature was raised by 2.5 degrees C. Of six brain regions investigated only the hypothalamus showed significant changes in receptor states, confirming its pivotal role in thermoregulation. Adrenergic receptors, studied by [3H]clonidine binding, showed a 36% decrease in binding following radiation after a 2.5 degrees C increase in body temperature, suggesting a mechanism to facilitate norepinephrine release. Norepinephrine may be speculated to maintain thermal homeostasis by activating heat dissipation. Muscarinic cholinergic receptors, studied by [3H]quinuclidinyl benzilate binding, showed a 65% increase in binding at the onset of radiation. This may be attributed to the release of acetylcholine in the hypothalamus in response to heat cumulation. The continued elevated binding during the period of cooling after radiation was shut off may suggest the existence of an extra-hypothalamic heat-loss pathway.

AI evidence extraction

Main findings

Rats exposed to 700 MHz microwave radiation at 15 mW/cm2 with a 2.5°C rise in body temperature showed significant receptor binding changes only in the hypothalamus among six brain regions examined. Hypothalamic [3H]clonidine binding (adrenergic receptors) decreased by 36% following radiation, while hypothalamic [3H]quinuclidinyl benzilate binding (muscarinic receptors) increased by 65% at the onset of radiation and remained elevated during cooling after exposure ended.

Outcomes measured

• Alpha-adrenergic receptor binding ([3H]clonidine) in brain regions
• Muscarinic cholinergic receptor binding ([3H]quinuclidinyl benzilate) in brain regions
• Radiation-induced hyperthermia (body temperature increase of 2.5°C)

Limitations

• Sample size not reported in the abstract
• Exposure duration not reported in the abstract
• Findings are in rats; human relevance not established in the abstract
• Hyperthermia is present (2.5°C increase), making it difficult to separate thermal from non-thermal effects based on the abstract alone

Suggested hubs

• mechanisms-neurotransmitters (0.78)
  Assesses hypothalamic adrenergic and muscarinic receptor binding changes during RF-induced hyperthermia.
• rf-thermal-effects (0.72)
  Exposure explicitly produces hyperthermia and examines thermoregulatory receptor responses.

{
    "study_type": "animal",
    "exposure": {
        "band": "RF",
        "source": null,
        "frequency_mhz": 700,
        "sar_wkg": null,
        "duration": null
    },
    "population": "Rats",
    "sample_size": null,
    "outcomes": [
        "Alpha-adrenergic receptor binding ([3H]clonidine) in brain regions",
        "Muscarinic cholinergic receptor binding ([3H]quinuclidinyl benzilate) in brain regions",
        "Radiation-induced hyperthermia (body temperature increase of 2.5°C)"
    ],
    "main_findings": "Rats exposed to 700 MHz microwave radiation at 15 mW/cm2 with a 2.5°C rise in body temperature showed significant receptor binding changes only in the hypothalamus among six brain regions examined. Hypothalamic [3H]clonidine binding (adrenergic receptors) decreased by 36% following radiation, while hypothalamic [3H]quinuclidinyl benzilate binding (muscarinic receptors) increased by 65% at the onset of radiation and remained elevated during cooling after exposure ended.",
    "effect_direction": "mixed",
    "limitations": [
        "Sample size not reported in the abstract",
        "Exposure duration not reported in the abstract",
        "Findings are in rats; human relevance not established in the abstract",
        "Hyperthermia is present (2.5°C increase), making it difficult to separate thermal from non-thermal effects based on the abstract alone"
    ],
    "evidence_strength": "low",
    "confidence": 0.7399999999999999911182158029987476766109466552734375,
    "peer_reviewed_likely": "yes",
    "keywords": [
        "microwave radiation",
        "700 MHz",
        "power density 15 mW/cm2",
        "hyperthermia",
        "thermoregulation",
        "hypothalamus",
        "alpha-adrenergic receptors",
        "muscarinic cholinergic receptors",
        "[3H]clonidine binding",
        "[3H]quinuclidinyl benzilate binding"
    ],
    "suggested_hubs": [
        {
            "slug": "mechanisms-neurotransmitters",
            "weight": 0.7800000000000000266453525910037569701671600341796875,
            "reason": "Assesses hypothalamic adrenergic and muscarinic receptor binding changes during RF-induced hyperthermia."
        },
        {
            "slug": "rf-thermal-effects",
            "weight": 0.7199999999999999733546474089962430298328399658203125,
            "reason": "Exposure explicitly produces hyperthermia and examines thermoregulatory receptor responses."
        }
    ]
}

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