Study type: Medical/biological study (experimental study)

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

Published in: Radiat Res 1987; 109 (1): 90-99

Aim of study (acc. to editor)

To investigate the involvement of adrenergic and muscarinic cholinergic receptors in radiation-induced hyperthermia.

Background/further details

[³H]-clonidine is a radioactive ligand used for the characterization of alpha-adrenergic receptors and [³H]-clonidine binding was used in this study as an indicator of the availability of alpha-adrenergic receptors in rats during and after microwave-induced hyperthermia. Physiological actions of acetylcholine in brain are most commonly mediated by muscarinic receptors. Specific [³H]-quinuclidinyl benzilate binding was used to assay the concentration of muscarinic binding sites.

Endpoint

Exposure

Exposure Parameters
Exposure 1: 700 MHz
Modulation type: CW
Exposure duration: 10 min
  • power density: 5 W/m² minimum (10 mW/cm², 15 mW/cm² and 20 mW/cm²)
  • SAR: 20 mW/g unspecified (unspecified) (at 15 mW/cm² incident power density)

Exposure 1

Main characteristics
Frequency 700 MHz
Type
Waveform
Charakteristic
Polarization
Exposure duration 10 min
Modulation
Modulation type CW
Exposure setup
Exposure source
Distance between exposed object and exposure source 1.8 m
Chamber anachoic chamber
Setup animals placed in a Plexiglas restrainer (6 in. long and 2.25 in diameter) which was placed on the table
Parameters
Measurand Value Type Method Mass Remarks
power density 5 W/m² minimum measured - 10 mW/cm², 15 mW/cm² and 20 mW/cm²
SAR 20 mW/g unspecified unspecified unspecified at 15 mW/cm² incident power density

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Investigated organ system:
Time of investigation:
  • during exposure
  • after exposure

Main outcome of study (acc. to author)

Of six brain regions investigated only the hypothalamus showed significant changes in receptor states. This confirms its pivotal role in thermoregulation. Adrenergic receptors showed a 36% decrease in binding following radiation after a 2.5°C increase in body temperature, suggesting a mechanism to facilitate norepinephrine release. Muscarinic receptors 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 exposure was shut off may suggest the existence of an extra-hypothalamic heat-loss pathway.

Study character:

Study funded by