Female Rats Show Greater Sensitivity to High-Strength Magnetic Fields

This dissertation discusses the investigation of sex differences in the response to magnetic field (MF) exposure and the role of the vestibular system and estrogen in the effects of MFs. Advances in magnetic resonance imaging are driving the development of higher resolution machines equipped with high-strength static MFs. The behavioral effects of high-strength MFs are largely uncharacterized. Our laboratory has previously shown that following high-strength static magnetic field (MF) exposure, male rats suppress normal rearing behavior, walk in circles, acquire a conditioned taste aversion (CTA), and express c-Fos in vestibular and visceral relays of the brainstem. These results suggest that the MF may interact with the vestibular system producing effects similar to rotation or motion sickness. Here, I provide evidence for sex differences in the response to MF-exposure by examining how fluctuations in endogenous estrogen across the female rat's estrous cycle and removal of the ovaries and subsequent hormone replacement influence the behavioral response to MF-exposure compared to male rats. I then provide evidence that the inner ear is required for both the behavioral and neural response to MF-exposure by showing that bilateral removal of the inner ear by chemical labyrinthectomy eliminates MF-induced CTA and MF-induced c-Fos expression in vestibular and visceral relays. I also demonstrate that estrogen influences the amount of c-Fos expression in the vestibular and visceral relays. Compared to ovariectomized rats, chronic estrogen replacement decreased c-Fos expression in the LC and SuV and reversed significant hemispheric asymmetries in other vestibular and visceral relays suggesting potential neural sites where estrogen could interact to influence the behavioral response to MF exposure. In addition, I provide evidence that the estrogen receptor subunits are present within specific areas of the vestibular and visceral relays that are responsive to MF-exposure and could potentially mediate the effects of estrogen.