Tryptophan metabolism via the kynurenine pathway may represent a key molecular link between sleep loss and cognitive dysfunction.
The results of this study introduce kynurenine pathway metabolism and formation of metabolite kynurenic acid as a novel molecular target contributing to sleep disruptions and cognitive impairments.
Authors: Machida M, Wellman LL, Fitzpatrick Bs ME, Hallum Bs O, Sutton Bs AM, Lonart G, Sanford LD.
“Glutamatergic cells in BLA can modulate the effects of stress on REM and can mediate effects of fear memory on sleep that can be independent of behavioral fear.”
The sleep electroencephalogram (EEG) is highly heritable in humans and yet little is known about the genetic basis of inter-individual differences in sleep architecture. The aim of this study was to identify associations between candidate circadian gene variants and the polysomnogram, recorded under highly controlled laboratory conditions during a baseline, overnight, 8 h sleep opportunity. A candidate gene approach was employed to analyze single-nucleotide polymorphisms from five circadian-related genes in a two-phase analysis of 84 healthy young adults (28 F; 23.21 ± 2.97 years) of European ancestry. A common variant in Period2 (PER2) was associated with 20 min less slow-wave sleep (SWS) in carriers of the minor allele than in noncarriers, representing a 22% reduction in SWS duration. Moreover, spectral analysis in a subset of participants (n = 37) showed the same PER2 polymorphism was associated with reduced EEG power density in the low delta range (0.25-1.0 Hz) during non-REM sleep and lower slow-wave activity (0.75-4.5 Hz) in the early part of the sleep episode. These results indicate the involvement of PER2 in the homeostatic process of sleep. Additionally, a rare variant in Melatonin Receptor 1B was associated with longer REM sleep latency, with minor allele carriers exhibiting an average of 65 min (87%) longer latency from sleep onset to REM sleep, compared to noncarriers. These findings suggest that circadian-related genes can modulate sleep architecture and the sleep EEG, including specific parameters previously implicated in the homeostatic regulation of sleep.
Wakefulness is driven by the widespread release of neuromodulators by the ascending arousal system. Yet, it is unclear how these substances orchestrate state-dependent, global changes in neuronal activity. Here, we show that neuromodulators induce increases in the extracellular K(+) concentration ([K(+)]e) in cortical slices electrically silenced by tetrodotoxin. In vivo, arousal was linked to AMPA receptor-independent elevations of [K(+)]e concomitant with decreases in [Ca(2+)]e, [Mg(2+)]e, [H(+)]e, and the extracellular volume. Opposite, natural sleep and anesthesia reduced [K(+)]e while increasing [Ca(2+)]e, [Mg(2+)]e, and [H(+)]e as well as the extracellular volume. Local cortical activity of sleeping mice could be readily converted to the stereotypical electroencephalography pattern of wakefulness by simply imposing a change in the extracellular ion composition. Thus, extracellular ions control the state-dependent patterns of neural activity.
This work delineates the normal oscillation and responsiveness of circulating monocytes and T lymphocytes in ten human volunteers over circadian time. Under normal circadian parameters, bimodal cytokine secretion was observed with the night peak caused by an increased responsiveness of monocytes, and the day peak corresponding to a higher absolute number of monocytes. T lymphocytes demonstrated an evening peak caused by both higher cell count and responsiveness. When subjected to a night shift schedule (acute circadian disruption) monocyte and T cells circulating phase was not changed but the responsiveness of both cell types was advanced (earlier expression of cytokine) after stimulation. This suggests that acute changes in sleep-wake cycles alter the cell intrinsic responsiveness to stimulation whereas parameters governing circulation may lag behind.
The preBotzinger complex in rats is a respiratory neuronal network driving inspiratory rhythm. Chronic intermittent hypoxia (as is the case in OSA) causes irregular firing of the preBotzinger complex. Dysrhythmia in the preBotzinger complex loosens the coupling of neuronal transmission with XIIn. Lipid peroxidation is increased in both the preBotzinger complex and XIIn as a result of chronic intermittent hypoxia. Treatment with antioxidant can reverse the instability in neuronal coupling caused by the exposure hypoxia. This work demonstrates the effect of hypoxia on rhythmic breathing in a salient neuronal network and provides a possible therapeutic strategy to re-establish rhythmic neuronal connectivity in this pathway.
This paper outlines the effect of caffeine on the human circadian clock, and verifies previously assumed yet unproven interactions between the drug and sleep timing. Using human subjects the authors determined that caffeine (a timed double shot of espresso) indeed delays the circadian phase (delays sleep onset), but more saliently perhaps, the authors demonstrate that bright light (3000 lux [about 1/3 of light on a sunny day] for 3 hours around the normal bed-time hour) was associated with an increased magnitude of delayed circadian phase. Using a human U2OS bmal:luc in vitro system the authors then show that the caffeine prolongs the circadian period through a adenosine receptor/cAMP pathway. This work is the first to mechanistically tie the widely used drug caffeine to delayed circadian phase in humans but understatedly also calls attention to the significant effect of light on circadian rhythm, which has implications for both hospital recovery environments and optimal bed-time routines for the population at large.
The authors compared the cellular responses of cultured human adult cardiac myocytes exposed to intermittent hypoxia and different conditions of continuous hypoxia and normoxia. Intermittent and constant severe hypoxia, but not constant mild hypoxia or normoxia, induced inflammation and cell injury in the myocytes as evidenced by lower cell count and viability, and greater cytokine secretion. The greatest cell injury occurred with intermittent severe hypoxia.
This work outlines circuitry involved in memory formation using a dual genetic reporter system for labeling learning-dependent cells, a mouse model of contextual fear learning and delivery of an amnestic agent. The authors determine that if an amnestic agent is given shortly after the conditioning shock, the animals behave as though they had never experienced the shock (do not freeze when a tone is administered in a cage) and have neurons in the circuit with decreased synaptic strength and spine density. But, optogenetic activation of the circuits that were active during (specific) memory formation causes the mouse to freeze (as though it remembered the shock). Therefore, although the memory of the fearful event (tone-shock) is established even if an amnestic agent is given, the ability to access the memory (recall) seems to be the inhibited process. The authors propose that intact neuronal connectivity patterns are important for memory formation and that synaptic strength may be involved in memory retrieval.
This paper investigates the relationship between sleep/wake states and astrocyte maintenance of the dendritic spine niche. In the awake or chronic sleep restriction states, synaptic associations are maintained indicating a role for the astrocyte in preserving synapses. This work provides a mechanistic glimpse of how the sleep state may be responsible for synaptic pruning important for long-term potentiation or long-term depression in memory consolidation.