To examine possible additive effects of agmatine and theta-burst stimulation patterned complex magnetic field treatments for contextual fear learning.
52 rats were injected immediatly prior to a fear conditioning procedure with saline (0.9%) or agmatine (4 mg/kg). In a conditioning chamber rats were given three 2 sec electrical footshocks (0.5 mA) delivered at 60 sec intervals. 24 hours later rats were scored for defensive freezing when they returned to the conditioning chamber for 8 min. Immediatly after fear conditioning rats were placed for 30 min into an exposure cage or sham exposure cage.
The rats were trained on seven pairs of testing days over a period of two months. Additionally, the relationship between the intensity of the ambient geomagnetic field and amounts of contextual fear learning was examined three hours prior, during and after fear conditioning.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
60 Hz
Modulation type:
pulsed
Exposure duration:
30 min
|
|
| Frequency | 60 Hz |
|---|---|
| Type | |
| Waveform | |
| Exposure duration | 30 min |
| Exposure source | |
|---|---|
| Setup | 3 pairs of solenoids positioned so that fields in x-, y- and z-axis were generated; fields combined to a rotating field with 2s orientation in each axis and 2 s field in all axes; rotation frequency 0.5 Hz |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 2 µT | peak value | measured | - | at 1 cm from any individual solenoid |
| magnetic flux density | 1.5 µT | peak value | measured | - | at the center |
| magnetic flux density | 200 µT | peak value | measured | - | in the corners |
Exposed rats showed a significant decrease in freezing compared to sham-exposed rats. Agmatine-treated rats showed a significant decrease in freezing compared to saline-treated rats. The rats treated with agmatine and given post-conditioning exposures froze signifcantly less than all the other groups.
Only for the sham-exposed rats the amount of learned fear was correlated with the intensity of the ambient geomagnetic conditions during the interval of the conditioning sessions: increased ambient geomagnetic activity was associated with decreased fear learning.
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