Effects of light therapy on sleep/wakefulness, daily rhythms, and the central orexin system in a diurnal rodent model of seasonal affective disorder.

BACKGROUND: Bright light therapy (BLT) is the first-line treatment for seasonal affective disorder. However, the neural mechanisms underlying BLT are unclear. To begin filling this gap, the present study examined the impact of BLT on sleep/wakefulness, daily rhythms, and the wakefulness-promoting orexin/hypocretin system in a diurnal rodent, Nile grass rats (Arvicanthis niloticus). METHODS: Male and female grass rats were housed under a 12:12 h light/dark cycle with dim light (50 lx) during the day. The experimental group received daily 1-h early morning BLT (full-spectrum white light, 10,000 lx), while the control group received narrowband red light for 4 weeks. Sleep/wakefulness and in-cage locomotor activity were monitored, followed by examination of hypothalamic prepro-orexin and orexin receptors OX1R and OX2R expression in corticolimbic brain regions. RESULTS: The BLT group had higher wakefulness during light treatment, better nighttime sleep quality, and improved daily rhythm entrainment compared to controls. The impact of BLT on the orexin system was sex- and brain region-specific, with males showing higher OX1R and OX2R in the CA1, while females showed higher prepro-orexin but lower OX1R and OX2R in the BLA, compared to same-sex controls. LIMITATIONS: The present study focused on the orexin system in a limited number of brain regions at a single time point. Sex wasn't a statistical factor, as male and female cohorts were run independently. CONCLUSIONS: The diurnal grass rats show similar behavioral responses to BLT as humans, thus could be a good model for further elucidating the neural mechanisms underlying the therapeutic effects of BLT.

Resolvins AT-D1 and E1 differentially impact functional outcome, post-traumatic sleep, and microglial activation following diffuse brain injury in the mouse.

Traumatic brain injury (TBI) is induced by mechanical forces which initiate a cascade of secondary injury processes, including inflammation. Therapies which resolve the inflammatory response may promote neural repair without exacerbating the primary injury. Specific derivatives of omega-3 fatty acids loosely grouped as specialized pro-resolving lipid mediators (SPMs) and termed resolvins promote the active resolution of inflammation. In the current study, we investigate the effect of two resolvin molecules, RvE1 and AT-RvD1, on post-traumatic sleep and functional outcome following diffuse TBI through modulation of the inflammatory response. Adult, male C57BL/6 mice were injured using a midline fluid percussion injury (mFPI) model (6-10min righting reflex time for brain-injured mice). Experimental groups included mFPI administered RvE1 (100ng daily), AT-RvD1 (100ng daily), or vehicle (sterile saline) and counterbalanced with uninjured sham mice. Resolvins or saline were administered daily for seven consecutive days beginning 3days prior to TBI to evaluate proof-of-principle to improve outcome. Immediately following diffuse TBI, post-traumatic sleep was recorded for 24h post-injury. For days 1-7 post-injury, motor outcome was assessed by rotarod. Cognitive function was measured at 6days post-injury using novel object recognition (NOR). At 7days post-injury, microglial activation was quantified using immunohistochemistry for Iba-1. In the diffuse brain-injured mouse, AT-RvD1 treatment, but not RvE1, mitigated motor and cognitive deficits. RvE1 treatment significantly increased post-traumatic sleep in brain-injured mice compared to all other groups. RvE1 treated mice displayed a higher proportion of ramified microglia and lower proportion of activated rod microglia in the cortex compared to saline or AT-RvD1 treated brain-injured mice. Thus, RvE1 treatment modulated post-traumatic sleep and the inflammatory response to TBI, albeit independently of improvement in motor and cognitive outcome as seen in AT-RvD1-treated mice. This suggests AT-RvD1 may impart functional benefit through mechanisms other than resolution of inflammation alone.

Meditation acutely improves psychomotor vigilance, and may decrease sleep need.

BACKGROUND: A number of benefits from meditation have been claimed by those who practice various traditions, but few have been well tested in scientifically controlled studies. Among these claims are improved performance and decreased sleep need. Therefore, in these studies we assess whether meditation leads to an immediate performance improvement on a well validated psychomotor vigilance task (PVT), and second, whether longer bouts of meditation may alter sleep need. METHODS: The primary study assessed PVT reaction times before and after 40 minute periods of mediation, nap, or a control activity using a within subject cross-over design. This study utilized novice meditators who were current university students (n = 10). Novice meditators completed 40 minutes of meditation, nap, or control activities on six different days (two separate days for each condition), plus one night of total sleep deprivation on a different night, followed by 40 minutes of meditation.A second study examined sleep times in long term experienced meditators (n = 7) vs. non-meditators (n = 23). Experienced meditators and controls were age and sex matched and living in the Delhi region of India at the time of the study. Both groups continued their normal activities while monitoring their sleep and meditation times. RESULTS: Novice meditators were tested on the PVT before each activity, 10 minutes after each activity and one hour later. All ten novice meditators improved their PVT reaction times immediately following periods of meditation, and all but one got worse immediately following naps. Sleep deprivation produced a slower baseline reaction time (RT) on the PVT that still improved significantly following a period of meditation. In experiments with long-term experienced meditators, sleep duration was measured using both sleep journals and actigraphy. Sleep duration in these subjects was lower than control non-meditators and general population norms, with no apparent decrements in PVT scores. CONCLUSIONS: These results suggest that meditation provides at least a short-term performance improvement even in novice meditators. In long term meditators, multiple hours spent in meditation are associated with a significant decrease in total sleep time when compared with age and sex matched controls who did not meditate. Whether meditation can actually replace a portion of sleep or pay-off sleep debt is under further investigation.