body temperatures before and after sleep onset in preterm neonates
Résumé
Title
Effects of chronic exposition to noise on homeostasis in juvenile rats
Introduction
One third of the developed countries population has a poor sleep quality
or reduced sleep duration. One of the cause of these complains is noise.
The noise is generally defined as an unwanted sound which can have
auditory but also extra-auditory effects on health. Furthermore, in OECD,
100 million peoples go through noise exposure exceeding 65dB(A) whereas
levels should not exceed the threshold of 55dB(A) because could provoke
awakening. The aim of this study is to see the effects a chronic high level
noise exposition on juvenile rats on sleep and homeostasis parameters.
Materials and methods
24 3-weeks old male Wistar rats (12 control vs 12 noise exposed) were
exposed or not to noise 5 weeks at 87.5 dB 50-20.000Hz, mixing
environmental and artificial noises during the light-rest period of the rat
(12h from 6:00 am to 6:00 pm). The noise level of control was under 65dB.
After 3 weeks of exposition, rats were surged to dispose polysomnographic
telemetric implants (EEGs and EMG). At 5th week of exposition, 24-hrs
polysomnography was performed and total duration (min, % of Total Sleep
Time, TST), frequency (ep/h), mean duration of episode (s) for Wake,
NREM, REM and Quiet Wakefulness were measured. The ratios NREM/TST
and REM/TST were calculated. Food and water intake and weight of the
animals were recorded. At the beginning of the 6th week,
plethysmography was set for 1 hour (10:00 to 11:00 in non noise-exposed
area) and apneas were analyzed in correlation with sleep states. The data
were analyzed with Statview software and expressed in Mean ± Standard
Deviation (SD). Depending on normality (Kolmogorov-Smirnov), two-way
ANOVA with PLSD Fisher post-test or Mann-Whitney analyses were
performed. Differences were considered significant at p<0.05. Significant
results (p<0.10) are given when consistent.
Results
The weight of noise group animals tended to increase compared to controls
(279.5±26.7 vs 290.6±33.3 g, p=0.055). Noise exposed animals ate more
(total quantity: +2.72 g/24h, p<0.001) as a result of increased number of
meals (+1.2 meals/24h, p=0.001) and increased average duration of a meal
(+153 s, p=0.002). Moreover, these animals drunk more (+7.3 mL/24h,
p<0.001).
The number of apneas significantly increased in noise exposed group
(1.1±1.9 vs 3.2±5.4 apnea/h, p=0.04), whatever the sleep states. Chronic
noise exposure significantly affected sleep with a diminution of Quiet
Wakefulness and NREM episodes (respectively -2.3 ep/h, p=0.05 and -2.4
ep/h, p=0.003) whereas mean duration of NREM episodes increased (17.6
s; p=0.058).
The other noise effects on sleep depend on nycthemeral period: during the
light-rest period (noise exposure), there was no significant modification of
sleep. In contrast, during the dark-activity period (no noise), total duration
of NREM sleep decreased (-3.1% of TST, p=0.017) at the expense of REM
sleep.
Conclusions
The chronic noise exposure at high-level exposure of 87.5 dB during the
light-rest period induced significant sleep disturbances with modification of
sleep microstructure without great modification of sleep macrostructure.
These effects generally occur during the dark-rest period. Indicators of
general homeostasis were also perturbed as shown by increased of body
weight, hyperphagia and sleep apnea.