Short-term sleep fragmentation enhances anxiety-related behavior: The role of hormonal alterations

Introduction

The neuroendocrine background of acute sleep fragmentation in obstructive sleep apnea and sleep fragmentation involvement in psychiatric comorbidities, common in these patients, are still largely unknown. The aim of this study was to determine the effects of short-term experimental sleep fragmentation on anxiety -like behavior and hormonal status in rats.

Methods

Male rats were adapted to treadmill (ON and OFF mode with belt speed set on 0.02m/s and 0.00m/s) and randomized to: 1) treadmill control (TC, only OFF mode); 2) motion, activity control (AC, 10min ON and 30min OFF mode) and 3) sleep fragmentation (SF, 30s ON and 90s OFF mode) group. Six hours later, the animals were tested in the open field, elevated plus maze and light/dark test (n = 8/group). Testosterone, estradiol, progesterone and corticosterone were determined in separate animal cohort immediately upon sleep fragmentation (n = 6/group).

Results

SF rats showed decreased rearings number, decreased time spent in the central area and increased thigmotaxic index compared to TC and AC rats in the open field test. Similarly, increased anxiety upon sleep fragmentation was observed in the elevated plus maze and the light/dark test. Significantly lower testosterone, estradiol and progesterone levels were determined in SF in comparison to AC and TC groups, while there was no significant difference in the levels of corticosterone.

Conclusion

Short term sleep fragmentation enhances anxiety-related behavior in rats, which could be partly mediated by the observed hormonal changes presented in the current study in form of testosterone, estradiol and progesterone depletion.

CSF prostaglandin D synthase is reduced in excessive daytime sleepiness

Lipocalin-type prostaglandin D synthase (L-PGDS) is a brain enzyme, which produces prostaglandin D(2), a substance with endogenous somnogenic effects. Using a standardized protocol for immunonephelometric determination of cerebrospinal fluid (CSF) L-PGDS levels, we show that CSF L-PGDS levels are significantly lower in 34 patients with excessive daytime sleepiness when compared with levels in 22 healthy controls. Thus, L-PGDS may represent the first neurochemical measure of excessive daytime sleepiness.

Increased hypocretin-1 levels in cerebrospinal fluid after REM sleep deprivation

Rat cisternal (CSF) hypocretin-1 in cerebrospinal fluid was measured after 6 or 96 h of REM sleep deprivation and following 24 h of REM sleep rebound. REM deprivation was found to increase CSF hypocretin-1 collected at zeitgeber time (ZT) 8 but not ZT0. Decreased CSF hypocretin levels were also observed at ZT8 after 24 h of REM sleep rebound. These results suggest that REM sleep deprivation activates and REM sleep rebound inhibits the hypocretin system. Increased hypocretin tone during REM deprivation may be important in mediating some of the effects of REM sleep deprivation such as antidepressant effects, hyperphagia and increased sympathetic activity.