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

Kwon

American Journal of Physiology-Regulatory, Integrative and Comp

et al. 2013

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High-strength static magnetic fields (>7 tesla) perturb the vestibular system causing dizziness, nystagmus, and nausea in humans; and head motion, locomotor circling, conditioned taste aversion, and c-Fos induction in brain stem vestibular nuclei in rodents. To determine the role of head orientation, mice were exposed for 15 min within a 14.1-tesla magnet at six different angles (mice oriented parallel to the field with the head toward B+ at 0°; or pitched rostrally down at 45°, 90°, 90° sideways, 135°, and 180°), followed by a 2-min swimming test. Additional mice were exposed at 0°, 90°, and 180° and processed for c-Fos immunohistochemistry. Magnetic field exposure induced circular swimming that was maximal at 0° and 180° but attenuated at 45° and 135°. Mice exposed at 0° and 45° swam counterclockwise, whereas mice exposed at 135° and 180° swam clockwise. Mice exposed at 90° (with their rostral-caudal axis perpendicular to the magnetic field) did not swim differently than controls. In parallel, exposure at 0° and 180° induced c-Fos in vestibular nuclei with left-right asymmetries that were reversed at 0° vs. 180°. No significant c-Fos was induced after 90° exposure. Thus, the optimal orientation for magnetic field effects is the rostral-caudal axis parallel to the field, such that the horizontal canal and utricle are also parallel to the field. These results have mechanistic implications for modeling magnetic field interactions with the vestibular apparatus of the inner ear (e.g., the model of Roberts et al. of an induced Lorenz force causing horizontal canal cupula deflection).

Section: Discussionsupporting

confidence: 91%

Section: Discussioncontrasting

confidence: 73%

Orientation within a high magnetic field determines swimming direction and laterality of c-Fos induction in mice

Kwon

American Journal of Physiology-Regulatory, Integrative and Comp

et al. 2013

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Journal of Applied Physiology

“…In fact, as estrogen upregulates P receptors (24), this mechanism is likely involved with the respiratory effects of P. E 2 and P receptors (ER-␣, ER-␤; PR-A, PR-B) were identified in many respiratory regions of the brain, including the nucleus of the solitary tract (38,39), the hypoglossal nuclei (4), and the motor nuclei of the phrenic nerve (4). In fact, some studies have reported an inhibitory effect of E 2 in some areas important for V E (10,44,46,49). Also, studies in OVX rats (8) and castrated cats (20,21) have demonstrated that administration of P combined with estrogen promotes an increase in pulmonary V E and hypercapnic ventilatory response through receptor-mediated mechanisms of action involving central and peripheral sites.…”

Section: Ovariectomy Hormonal Replacement V E Metabolism and Tbmentioning

confidence: 99%

Ventilatory, metabolic, and thermal responses to hypercapnia in female rats: effects of estrous cycle, ovariectomy, and hormonal replacement

Marques

Carvalho

Silva

et al. 2015

The aim of this study was to examine how estrous cycle, ovariectomy, and hormonal replacement affect the respiratory [ventilation (V̇e), tidal volume, and respiratory frequency], metabolic (V̇o2), and thermoregulatory (body temperature) responses to hypercapnia (7% CO2) in female Wistar rats. The parameters were measured in rats during different phases of the estrous cycle, and also in ovariectomized (OVX) rats supplemented with 17β-estradiol (OVX+E2), with a combination of E2 and progesterone (OVX+E2P), or with corn oil (OVX+O, vehicle). All experiments were conducted on day 8 after ovariectomy. The intact animals did not present alterations during normocapnia or under hypercapnia in V̇e, tidal volume, respiratory frequency, V̇o2, and V̇e/V̇o2 in the different phases of the estrous cycle. However, body temperature was higher in female rats on estrus. Hormonal replacement did not change the ventilatory, thermoregulatory, or metabolic parameters during hypercapnia, compared with the OVX animals. Nevertheless, OVX+E2, OVX+E2P, and OVX+O presented lower hypercapnic ventilatory responses compared with intact females on the day of estrus. Also, rats in estrus showed higher V̇e and V̇e/V̇o2 during hypercapnia than OVX animals. The data suggest that other gonadal factors, besides E2 and P, are possibly involved in these responses.

“…Exposure to magnetic fields at 7T or above can serve as the unconditioned stimulus for conditioned taste aversion or avoidance (CTA) learning, suggesting that exposure has an aversive component [14, 15, 17]. Consistent with stimulation of the vestibular system, magnetic field exposure induces c-Fos in vestibular and visceral relays of the rat brainstem [18, 19]. The effects of the high magnetic field on locomotion and CTA are maximal after head exposure [20].…”

Section: Introductionmentioning

confidence: 99%

Head tilt in rats during exposure to a high magnetic field

Cassell

Carella

et al. 2012

Physiology & Behavior

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During exposure to high strength static magnetic fields, humans report vestibular symptoms such as vertigo, apparent motion, and nausea. Rodents also show signs of vestibular perturbation after magnetic field exposure at 7 tesla (T) and above, such as locomotor circling, activation of vestibular nuclei, and acquisition of conditioned taste aversions. We hypothesized that the acute effects of the magnetic field might be seen as changes in head position during exposure within the magnet. Using a yoked restraint tube that allowed movement of the head and neck, we found that rats showed an immediate and persistent deviation of the head during exposure to a static 14.1 T magnetic field. The direction of the head tilt was dependent on the orientation of the rat in the magnetic field (B), such that rats oriented head-up (snout towards B+) showed a rightward tilt of the head, while rats oriented head–down (snout towards B−) showed a leftward tilt of the head. The tilt of the head during magnet exposure was opposite to the direction of locomotor circling immediately after exposure observed previously. Rats exposed in the yoked restraint tube showed significantly more locomotor circling compared to rats exposed with the head restrained. There was little difference in CTA magnitude or extinction rate, however. The deviation of the head was seen when the rats were motionless within the homogenous static field; movement through the field or exposure to the steep gradients of the field was not necessary to elicit the apparent vestibulo-collic reflex.