c-Fos induction by a 14 T magnetic field in visceral and vestibular relays of the female rat brainstem is modulated by estradiol

Abstract

There is increasing evidence that high magnetic fields interact with the vestibular system of humans and rodents. In rats, exposure to high magnetic fields of 7 T or above induces locomotor circling and leads to a conditioned taste aversion if paired with a novel taste. Sex differences in the behavioral responses to magnetic field exposure have been found, such that female rats show more locomotor circling and enhanced conditioned taste aversion compared to male rats. To determine if estrogen modulates the neural response to high magnetic fields, c-Fos expression after 14 T magnetic field exposure was compared in ovariectomized rats and ovariectomized rats with estradiol replacement. Compared to sham exposure, magnetic field exposure induced significantly more c-Fos positive cells in the nucleus of the solitary tract and the parabrachial, medial vestibular, prepositus, and supragenualis nuclei. Furthermore, there was a significant asymmetry in c-Fos induction between sides of the brainstem in several regions. In ovariectomized rats, there was more c-Fos expressed in the right side compared to left side in the locus coeruleus and parabrachial, superior vestibular, and supragenualis nuclei; less expression in the right compared to left side of the medial vestibular; and no asymmetry in the prepositus nucleus and the nucleus of the solitary tract. Chronic estradiol treatment modulated the neural response in some regions: less c-Fos was induced in the superior vestibular nucleus and locus coeruleus after estradiol replacement; estradiol treatment eliminated the asymmetry of c-Fos expression in the locus coeruleus and supragenualis nucleus, created an asymmetry in the prepositus nucleus and reversed the asymmetry in the parabrachial nucleus. These results suggest that ovarian steroids may mediate sex differences in the behavioral responses to magnetic field exposure at the level of visceral and vestibular nuclei of the brainstem.

Figure 1

Open-field locomotor behavior was scored for tight circling and rearing following 30-min magnetic field-exposure or sham-exposure. A. Only magnet-exposed rats circled and there was no difference in the number of circles between OVX and OVX+E rats. B. The latency to circle was significantly lower in OVX compared to OVX+E rats, * p < 0.01. C. Magnetic field-exposure (black bars) suppressed rearing in both OVX and OVX+E rats compared to sham-exposed rats (white bars); * p < 0.001.

Figure 2

Example photomicrographs of c-Fos induction in vestibular relays after sham exposure (A,D) or after 30-min magnetic field exposure in OVX rats (B,E) or OVX+E rats (C,F). IV, fourth ventricle; MeV, medial vestibular nucleus; Prp, prepositus nucleus, VII, genu of the 7th cranial nerve; SGe, supragenulis nucleus; SuV, superior vestibular nucleus.

Figure 3

Example photomicrographs of c-Fos induction in visceral relays after sham exposure (A,D) or after 30-min magnetic field exposure in OVX rats (B,E) or OVX+E rats (C,F). IV, fourth ventricle; cc, central canal; AP, area postrema; NTS, nucleus of the solitary tract; LC, locus coeruleus.

Figure 4

Quantification of c-Fos positive cells in sham-exposed (white and striped bars) or magnet-exposed (black and gray bars) rats in vestibular (A) and visceral relays (B). The bilateral counts (mean ± SEM) through each section are shown. MeV = medial vestibular nucleus, Prp = prepositus nucleus, SuV = superior vestibular nucleus, SGe = supragenualis nucleus, NTS = nucleus of the solitary tract, PBN = parabrachial nucleus, LC = locus coeruleus. * p < 0.05 within group v. sham-exposed rats; # p < 0.05 within magnet-exposed rats, OVX v. OVX+E.

Figure 5

Number of c-Fos positive cells after magnetic field exposure in the right side of each brain region, expressed as a percentage of c-Fos-positive cells in the left side of each brain region, for OVX (white bars) and OVX+E (black bars) rats in vestibular (A) and visceral relays (B). A significant difference from 100% indicates an asymmetrical induction of c-Fos. * p < 0.05 left v. right side, # p < 0.05 OVX vs. OVX+E.