The olfactory bulb plays a fundamental role in rat social recognition, e.g., of family members, and it is suggested that estrogen plays also an important role in social behavior. Studies demonstrated that mice lacking estrogen receptors showed modified social behavior. In a previous study (Reyes-Guerrero et al. 2006), the authors demonstrated that social recognition in ovariectomized rats was improved by estrogen supplement and exposure to an extremely low frequency magnetic field.
Female virgin rats were divided into the following groups (n=20 each): 1) exposure of intact rats to the magnetic field, 2) exposure of ovariectomized rats to the magnetic field, 3) exposure of ovariectomized rats supplemented with 17 β-estradiol (25 µg/kg daily, subcutaneous) to the magnetic field, 4) sham exposure of ovariectomized rats supplemented with estradiol, 5) sham exposure of ovariectomized rats, 6) sham exposure of intact rats. Each group was divided into 2 subgroups (n=10 each); one subgroup was exposed for 9 days, the other one for 30 days.
|Exposure duration||for 2 hours/day for 9 days|
|Setup||exposure system consisted of a chamber with a pair of circular double-wrapped Helmholtz coils, each made of 180 turns of 18-gage copper wire and with an internal diameter of 36 cm; coils were placed symmetrically one on each side of the experimental area (50 x 50 x 18 cm3) along the axis, separated by a distance equal to the radius of the coil and connected in parallel; field was uniform; experiments were performed at 22-23°C room temperature|
|Sham exposure||A sham exposure was conducted.|
|Additional info||sham-exposure followed the same protocol, but with the coils turned off|
Social recognition was significantly impaired in ovariectomized rats exposed to the magnetic field (group 2) compared to intact sham exposed rats (group 6) after 9 and 30 days of exposure. This effect could be negated by supplement of 17 β-estradiol (group 3). After 30 days of exposure, also intact rats exposed to the magnetic field (group 1) showed significantly impaired social recognition compared to all groups without magnetic field exposure.
The authors state, that the protein expression data indicate that the amount of α- and β-estradiol receptors may be modified by exposure to the magnetic field and that this modification in the receptors correlates with changes in the olfactory behavior. However, no significant effect of the magnetic field alone on the protein expression of estrogen receptors can be seen. (remark EMF-Portal: results and conclusions are not consistent and not comprehensive with respect to the figures.)
The authors conclude that exposure of rats to a 60 Hz magnetic field might alter social recognition behavior. Supplement of estrogens might protect from this effect and could increase the expression of estrogen receptors in the olfactory bulb, which might play a role in olfactory memory.