Stroboscopic lighting with intensity synchronized to rotation velocity alleviates motion sickness gastrointestinal symptoms and motor disorders in rats

Abstract

Motion sickness (MS) is caused by mismatch between conflicted motion perception produced by motion challenges and expected "internal model" of integrated motion sensory pattern formed under normal condition in the brain. Stroboscopic light could reduce MS nausea symptom via increasing fixation ability for gaze stabilization to reduce visuo-vestibular confliction triggered by distorted vision during locomotion. This study tried to clarify whether MS induced by passive motion could be alleviated by stroboscopic light with emitting rate and intensity synchronized to acceleration-deceleration phase of motion. We observed synchronized and unsynchronized stroboscopic light (SSL: 6 cycle/min; uSSL: 2, 4, and 8 cycle/min) on MS-related gastrointestinal symptoms (conditioned gaping and defecation responses), motor disorders (hypoactivity and balance disturbance), and central Fos protein expression in rats receiving Ferris wheel-like rotation (6 cycle/min). The effects of color temperature and peak light intensity were also examined. We found that SSL (6 cycle/min) significantly reduced rotation-induced conditioned gaping and defecation responses and alleviated rotation-induced decline in spontaneous locomotion activity and disruption in balance beam performance. The efficacy of SSL against MS behavioral responses was affected by peak light intensity but not color temperature. The uSSL (4 and 8 cycle/min) only released defecation but less efficiently than SSL, while uSSL (2 cycle/min) showed no beneficial effect in MS animals. SSL but not uSSL inhibited Fos protein expression in the caudal vestibular nucleus, the nucleus of solitary tract, the parabrachial nucleus, the central nucleus of amygdala, and the paraventricular nucleus of hypothalamus, while uSSL (4 and 8 cycle/min) only decreased Fos expression in the paraventricular nucleus of hypothalamus. These results suggested that stroboscopic light synchronized to motion pattern might alleviate MS gastrointestinal symptoms and motor disorders and inhibit vestibular-autonomic pathways. Our study supports the utilization of motion-synchronous stroboscopic light as a potential countermeasure against MS under abnormal motion condition in future.

Keywords: Fos protein; gastrointestinal symptoms; motion sickness; motor disorders; stroboscopic light.

Figure 1

Images illustrating the manner of stroboscopic lighting treatment during the Ferris wheel-like rotation in rats. (A) Top view of the plexiglass box of the rotation device that was equipped with four sets of LEDs mounted on the side wall of four separate chambers. The LEDs were connected to a controller which was used to set lighting parameters prior to the experiment. The stroboscopic light system was powered by a lithium battery fixed on the frame of the rotation device. (B) The schematic diagram showing the change of rotation angular velocity (120°/s at peak) and (C) stroboscopic light intensity (100 Lm at peak) as a function of time during rotation treatment in Experiment 1. LED emitting rate was set in synchronized (6 cycle/min, light intensity was represented by red lines) or unsynchronized (2, 4, and 8 cycle/min; light intensity was represented by blue lines) manners relative to the acceleration–deceleration rotation circle. The color temperature was set at 6,000 and 3,000 K as cool and warm light, respectively. The peak light intensity was adjusted as requested in Experiment 2 (50, 100, or 200 Lm) and Experiment 3 (100 Lm). LED, light-emitting diode; SSL, synchronized stroboscopic light; uSSL, unsynchronized stroboscopic light.

Figure 2

Effects of synchronized (6 cycle/min) or unsynchronized stroboscopic light (2, 4, and 8 cycle/min) at 100 Lm on defecation (A) and conditioned gaping (B) induced by rotation in rats. Rot, rotation stimulation; Sta, static control treatment; SSL, synchronized stroboscopic light; uSSL, unsynchronized stroboscopic light; CL, cool light; WL, warm light. Data are expressed as mean ± S.E. *P < 0.05, **P < 0.01, ***P < 0.001 vs. the Sta control group; ^#P < 0.001 vs. the Rot non-lighting group; ^ΔP < 0.05, ^ΔΔP < 0.01, ^ΔΔΔP < 0.001 vs. the corresponding SSL (6 cycle/min) Rot group with the same color temperature.

Figure 3

Effects of synchronized (6 cycle/min) or unsynchronized stroboscopic light (2, 4, and 8 cycle/min) at 100 Lm on hypoactivity and balance disturbance induced by rotation in rats. Spontaneous locomotion activity was characterized by total distance traveled (A) and immobile duration (B). Motor coordination was assessed by measuring the time to traverse the balance beam (C). Rot, rotation stimulation; Sta, static control treatment; SSL, synchronized stroboscopic light; uSSL, unsynchronized stroboscopic light; CL, cool light; WL, warm light. Data are expressed as mean ± S.E. *P < 0.01, **P < 0.01, ***P < 0.001 vs. the Sta control group; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 vs. the Rot non-lighting group. ^ΔP < 0.05, ^ΔΔP < 0.01, ^ΔΔΔP < 0.001 vs. the corresponding SSL (6 cycle/min) Rot group with the same color temperature.

Figure 4

Effects of synchronized stroboscopic light (6 cycle/min, warm light) with different peak intensities (50, 100, and 200 Lm) on defecation (A) and conditioned gaping (B) induced by rotation in rats. Rot, rotation stimulation; Sta, static control treatment. Data are expressed as mean ± S.E. *P < 0.001 vs. the Sta group; ^#P < 0.001 vs. the Rot non-lighting group. ^ΔP < 0.01, ^ΔΔP < 0.001 vs. the 50 Lm Rot group.

Figure 5

Effects of synchronized stroboscopic light (6 cycle/min, warm light) with different peak intensities (50, 100, and 200 Lm) on hypoactivity and balance disturbance induced by rotation in rats. Spontaneous locomotion activity was characterized by total distance traveled (A) and immobile duration (B), while balance performance was characterized by the time to cross the elevated balance beam (C). Rot, rotation stimulation; Sta, static control treatment. Data are expressed as mean ± S.E. *P < 0.05, **P < 0.001 vs. the Sta control group; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 vs. the Rot non-lighting group; ΔP < 0.05, ΔΔP < 0.01, ΔΔΔP < 0.001 vs. the 50 Lm Rot group.

Figure 6

Number of Fos-labeled neurons in the vestibulo-autonomic and stress-related areas in rats receiving synchronized or unsynchronized stroboscopic lighting at 100 Lm during rotation. Fos-labeled neurons were quantified in the caudal vestibular nucleus [CVN, (A)], the nucleus of solitary tract [NTS, (B)], the parabrachial nucleus [PBN, (C)], the central amygdala [CeA, (D)], the locus ceruleus [LC, (E)], and the paraventricular hypothalamus nucleus [PVN, (F)]. Rot, rotation stimulation; Sta, static control treatment; SSL, synchronized stroboscopic light; uSSL, unsynchronized stroboscopic light; data are expressed as mean ± S.E. *P < 0.01, **P < 0.01, ***P < 0.001 vs. the Sta control group; ^#P < 0.05, ^##P < 0.01 vs. the Rot non-lighting group. ^ΔP < 0.05, ^ΔΔP < 0.01 vs. the 6 cycle/min Rot group.

Figure 7

Representative photomicrographs showing Fos immunolabeling in the vestibulo-autonomic and stress-related areas in rats receiving synchronized or unsynchronized stroboscopic lighting at 100 Lm during rotation. Fos-labeling was presented in the caudal vestibular nucleus [CVN, (A1–A6)], the nucleus of solitary tract [NTS, (B1–B6)], the parabrachial nucleus [PBN, (C1–C6)], the central amygdala [CeA, (D1–D6)], the locus ceruleus [LC, (E1–E6)], and the paraventricular nucleus of hypothalamus [(PVN, (F1–F6)]. Rot, rotation stimulation; Sta, static control treatment; scale bars = 500 μm.