Study type: Medical/biological study (experimental study)

Thermal analgesic effects from weak, complex magnetic fields and pharmacological interactions med./bio.

Published in: Pharmacol Biochem Behav 2004; 78 (2): 217-227

Aim of study (acc. to editor)

To study thermal analgesic effects from weak, complex magnetic fields and pharmacological interactions in rats.

Background/further details

Rats were placed on a thermal plate that was maintained at 55°C. Once the rat was observed to lick one hind feet twice, the rat was removed from the apparatus.
Several experiments were performed: 1) electrical versus thermal analgesia; 2) intensity dependence of analgesia (exposure to 3 µT (the usual), 0.3 µT, or about 30 nT); 3) spatial parameters of field (usual field parameters or the same field condition within a Helmholtz coil); 4) comparison of two complex patterns (the efficacy of a frequency modulated pattern was compared with the typical burst-firing pattern); 5) verifying the specifity of experiment 4; 6) interactions between two types of magnetic fields (burst-firing magnetic field and frequency modulated magnetic field) and morphine (4 mg/kg) or agmatine (10 mg/kg); 7) naloxone (1 mg/kg) blocking of morphine and burst-firing magnetic field analgesia.

Endpoint

Exposure

Exposure Parameters
Exposure 1:
  • unspecified
Modulation type: pulsed
Exposure duration: once every 4 s for 30 min
Exposure 2:
  • unspecified
Modulation type: pulsed
Exposure duration: intermittent, once every 4 sec for 30 min
Exposure 3:
  • unspecified
Modulation type: pulsed
Exposure duration: intermittent, once every 4 sec for 30 min
Exposure 4:
  • unspecified
Modulation type: FM, pulsed
Exposure duration: intermittent, once every 4 sec for 30 min (burst firing pattern) or continuous for 30 min (FM wave)
-
Exposure 5:
  • unspecified
Modulation type: FM, pulsed
Exposure duration: for 30 min; continuous in the case of frequency modulated constant wave and intermittent, every 4 s in the case of burst firing pattern and the intermittent FM
-
Exposure 6:
  • unspecified
Modulation type: FM, pulsed, CW
Exposure duration: once every 4 s for 30 min or continuously for 30 min
-
Exposure 7:
  • unspecified
Modulation type: pulsed
Exposure duration: once every 4 s for 30 min
-

Exposure 1

Main characteristics
Frequency
  • unspecified
Type
Exposure duration once every 4 s for 30 min
Modulation
Modulation type pulsed
Additional info

burst-firing pattern

Exposure setup
Exposure source
Setup rats placed inside a 25 cm x 25 cm x 25 cm plastic cage with a metal floor grid between a pair of solenoids
Sham exposure A sham exposure was conducted.
Additional info rats were divided into 6 groups: i) sham exposure ii) 5 min magnetic field + 25 min sham field iii) 25 min sham field + 5 min magnetic field iv) 15 min magnetic field + 15 min sham field v) 15 min sham field + 15 min magnetic field vi) 30 min magnetic field
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 1 µT - - - -
cf. remarks - - - - U = 5 V

Exposure 2

Main characteristics
Frequency
  • unspecified
Type
Exposure duration intermittent, once every 4 sec for 30 min
Modulation
Modulation type pulsed
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 3 µT - - - -
magnetic flux density 0.3 µT - - - -
magnetic flux density 0.03 µT - - - -

Exposure 3

Main characteristics
Frequency
  • unspecified
Type
Exposure duration intermittent, once every 4 sec for 30 min
Modulation
Modulation type pulsed
Exposure setup
Exposure source
Setup experiment was done i) with the setup of E1 and ii) within a Helmholtz coil
Parameters
Measurand Value Type Method Mass Remarks
magnetic flux density 0.5 µT - - - -
magnetic flux density 1 µT - - - -
magnetic flux density 2.5 µT - - - -

Exposure 4

Main characteristics
Frequency
  • unspecified
Type
Exposure duration intermittent, once every 4 sec for 30 min (burst firing pattern) or continuous for 30 min (FM wave)
Modulation
Modulation type FM, pulsed
Additional info

burst firing pattern FM modulated constant wave

Exposure setup
Exposure source
Parameters

No parameters are specified for this exposure.

Exposure 5

Main characteristics
Frequency
  • unspecified
Type
Exposure duration for 30 min; continuous in the case of frequency modulated constant wave and intermittent, every 4 s in the case of burst firing pattern and the intermittent FM
Modulation
Modulation type FM, pulsed
Additional info

i) burst firing pattern ii) FM constant wave iii) FM once every 4 s

Exposure setup
Exposure source
Setup this experiment was done with i) a burst firing pattern once every 4 s ii) with a frequency modulated constant wave iii) with a frequency modulated signal once every 4 s
Sham exposure A sham exposure was conducted.
Parameters

No parameters are specified for this exposure.

Exposure 6

Main characteristics
Frequency
  • unspecified
Type
Exposure duration once every 4 s for 30 min or continuously for 30 min
Modulation
Modulation type FM, pulsed, CW
Additional info

i) burst firing pattern ii) FM constant wave

Exposure setup
Exposure source
Setup before exposure rats got a subcutaneous injection of either morphine sulphate, agmatine or physiological saline; exposure was either to a burst firing pattern or a FM constant wave
Sham exposure A sham exposure was conducted.
Parameters

No parameters are specified for this exposure.

Exposure 7

Main characteristics
Frequency
  • unspecified
Type
Exposure duration once every 4 s for 30 min
Modulation
Modulation type pulsed
Additional info

burst firing pattern

Exposure setup
Exposure source
Setup rats got additional injections with either saline, morphine or maloxone
Additional info rats were divided into 6 gruops: i) saline injection + saline injection + sham exposure ii) saline injection + saline injection + magnetic field iii) morphine injection + maloxone injection + sham exposure iv)morphine injection + maloxone injection + magnetic field v) saline injection + maloxone injection + sham exposure vi) saline injection + maloxone injection + magnetic field
Parameters

No parameters are specified for this exposure.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

In several experiments, robust analgesia (equivalent to about 4 mg/kg of morphine) in rats to thermal stimuli following exposures to weak complex magnetic fields was explored. The analgesia occurred when patterns of magnetic fields with burst-firing-like configurations were presented once every approximately 4 s (for 30 min). The effects were intensity dependent. A different frequency modulated pattern produced analgesic effects more quickly. Analgesia following exposure to the burst-firing magnetic fields were augmented conspicuously by preinjections of morphine or agmatine, but blocked by naloxone.
The data of these experiments indicate that rational design of the temporal structure of weak magnetic fields may be a novel, inexpensive, and reliable technique for elevating thresholds to some classes of painful stimuli.

Study character:

Study funded by

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