Rocking has long been known to promote sleep in infants and, more recently, also in adults, increasing NREM sleep stage N2 and enhancing EEG slow waves and spindles. Nevertheless, whether rocking also promotes sleep in other species, and what the underlying mechanisms are, has yet to be explored. In the current study, C57BL/6J mice equipped with EEG and EMG electrodes were rocked laterally during their main sleep period, i.e., the 12-h light phase. We observed that rocking affected sleep in mice with a faster optimal rate than in humans (1.0 versus 0.25 Hz). Specifically, rocking mice at 1.0 Hz increased time spent in NREM sleep through the shortening of wake episodes and accelerated sleep onset. Although rocking did not increase EEG activity in the slow-wave and spindle-frequency ranges in mice, EEG theta activity (6-10 Hz) during active wakefulness shifted toward slower frequencies. To test the hypothesis that the rocking effects are mediated through the vestibular system, we used the otoconia-deficient tilted (tlt) mouse, which cannot encode linear acceleration. Mice homozygous for the tlt mutation were insensitive to rocking at 1.0 Hz, while the sleep and EEG response of their heterozygous and wild-type littermates resembled those of C57BL/6J mice. Our findings demonstrate that rocking also promotes sleep in the mouse and that this effect requires input from functional otolithic organs of the vestibule. Our observations also demonstrate that the maximum linear acceleration applied, and not the rocking rate per se, is key in mediating the effects of rocking on sleep.

Experimental evidence has demonstrated that several aspects of adult neural stem cells (NSCs), including their quiescence, proliferation, fate specification and differentiation, are regulated by epigenetic mechanisms. These control the expression of specific sets of genes, often including those encoding for small non-coding RNAs, indicating a complex interplay between various epigenetic factors and cellular functions.

MicroRNAs (miRNAs) are key post-transcriptional regulators of gene expression that have been implicated in a plethora of neuronal processes. Nevertheless, their role in regulating brain activity in the context of sleep has so far received little attention. To test their involvement, we deleted mature miRNAs in post-mitotic neurons at two developmental ages, i.e., in early adulthood using conditional Dicer knockout (cKO) mice and in adult mice using an inducible conditional Dicer cKO (icKO) line. In both models, electroencephalographic (EEG) activity was affected and the response to sleep deprivation (SD) altered; while the rapid-eye-movement sleep (REMS) rebound was compromised in both, the increase in EEG delta (1 to 4 Hz) power during non-REMS (NREMS) was smaller in cKO mice and larger in icKO mice compared to controls. We subsequently investigated the effects of SD on the forebrain miRNA transcriptome and found that the expression of 48 miRNAs was affected, and in particular that of the activity-dependent miR-709 . In vivo inhibition of miR-709 in the brain increased EEG power during NREMS in the slow-delta (0.75 to 1.75 Hz) range, particularly after periods of prolonged wakefulness. Transcriptome analysis of primary cortical neurons in vitro revealed that miR-709 regulates genes involved in glutamatergic neurotransmission. A subset of these genes was also affected in the cortices of sleep-deprived, miR-709 -inhibited mice. Our data implicate miRNAs in the regulation of EEG activity and indicate that miR-709 links neuronal activity during wakefulness to brain synchrony during sleep through the regulation of glutamatergic signaling.