Lowers wake signal
Orexin signaling
Also searched as Orexin signaling.
The balance here is timing, the mirror of adenosine. Orexin is the wake signal — raised, it drives sustained attention and cholinergic tone; the cost shown here is sleep. You want it high by day and low at night. Loss of orexin neurons causes narcolepsy; the newer insomnia drugs are orexin blockers. Neither direction is the answer on its own.
In depth
The wakefulness and appetite peptide, and a genuine two-way system. A systematic review of 30 studies found orexin neurons activated by low glucose and suppressed by high — a counter-regulatory loop, not a one-way arrow.
What drives it
Blood-sugar support reduces it.
Burdakov 2006, Neuron 50:711 — orexin/hypocretin neurons are glucose-inhibited: rising extracellular glucose hyperpolarizes them via tandem-pore (K2P) K+ channels. PMID 16731510
Glycine calming reduces it.
Anatomical rather than inferred. IMMUNOELECTRON microscopy showed GlyT2-immunoreactive terminals making symmetrical synaptic contacts with the SOMATA and dendrites of orexin neurons, and double-labeling localized glycine receptor alpha subunits in the postsynaptic membrane. Not a pathway deduced from behavior — the synapse was photographed. The consequence: the Glycine → Sleep link and the Orexin → Sleep link are both drawn with opposite signs, and this edge shows they are not independent inputs. Part of what glycine does to sleep it does by silencing the wake peptide. The authors are careful: glycinergic inhibition of orexin neurons might play a role in physiological sleep regulation — the anatomy is established, the functional contribution inferred. PMC3174993
What it drives
It reduces Sleep.
Chemelli 1999, Cell 98:437 — orexin/hypocretin stabilizes wakefulness; loss of orexin neurons causes narcolepsy. DOI 10.1016/s0092-8674(00)81973-x. Orexin/hypocretin neurons of the lateral hypothalamus are critical for wakefulness, and their loss causes narcolepsy. Causal in both directions in vivo: optogenetically activating GABAergic neurons inhibits orexin neurons and makes awake mice transition to sleep; conversely, microinjecting a selective adenosine A1 antagonist into the orexinergic lateral hypothalamus — removing adenosine's brake — produced a significant increase in wakefulness with reduced sleep, both spontaneously and during recovery sleep after 6 h deprivation (PMID 18440150). A precise limit from that same experiment: blocking the adenosine brake lengthened the latency to non-REM sleep but total slow-wave (delta) activity during recovery sleep was unaffected — orexin gates when you fall asleep, not how deeply you sleep once you do. Orexin also forms a wake-maintaining loop with glutamatergic neurons of the paraventricular thalamus. Species: rat and mouse. doi 10.1016/s0092-8674(00 · PMID 18440150
It increases Sustained focus.
Orexin is the wake signal, and it is upstream of every other driver of this pathway: orexin projections excite wake-promoting systems, including locus coeruleus norepinephrine, dorsal raphe serotonin, tuberomammillary histamine and basal FOREBRAIN/BRAINSTEM acetylcholine neurons — and the LC expresses orexin receptor 1 specifically. It also projects to the VTA. Noradrenaline, acetylcholine and dopamine are three of the five drivers of focus on the map; orexin sits on all three. Causal, and fast: orexin neurons are more active during wake than sleep, fire just before waking, and cause waking within several seconds when optogenetically stimulated. Orexin administration lengthens and orexin disruption shortens continuous periods of wakefulness. Human loss-of-function settles necessity: a selective loss of orexin neurons is found in narcolepsy, in humans, dogs and rodents — remove these neurons and wakefulness cannot be held. And it opens a further dimension: orexin neurons ARE regulated by peripheral metabolic cues including ghrelin, leptin and glucose concentration, providing a link between energy homeostasis and arousal states. Attention has a fuel dependency that the neurotransmitters alone could never have shown. Inputs from the LIMBIC system also regulate orexin neurons to evoke emotional arousal and fear-related responses; that possible orexin-anxiety link is not drawn here. doi 10.3389/fphys.2017.00357 · PMC4335648
It increases Alertness chemical.
10.1523/JNEUROSCI.20-20-07760.2000 — hub edge,Orexin projections excite locus coeruleus noradrenergic neurons, and the LC expresses orexin receptor 1 specifically. Lesion evidence confirms the arm carries traffic: ablating LC noradrenergic neurons attenuated the effect of a dual orexin-receptor antagonist on REM sleep. doi 10.1523/JNEUROSCI.20-20-07760.2000
It increases Memory chemical.
Hub edge,Orexin projections excite basal forebrain and brainstem acetylcholine neurons, with dense innervation of the laterodorsal and pedunculopontine tegmental nuclei. Lesion evidence again separates the arms: ablating basal forebrain cholinergic neurons attenuated an orexin antagonist's effect on nrem sleep without affecting REM, while LC ablation did the opposite — the cholinergic and noradrenergic arms carry different parts of the signal. PMC4801942
It reduces Supports weight management.
10.3389/fendo.2020.00145 — the peptide is named for appetite — orexin, from the Greek — and acutely it does promote feeding. Yet losing it makes animals and people fat while they EAT less. The human natural experiment: narcolepsy type 1 is caused by loss of more than 90 percent of orexin-producing neurons, and those patients show significantly higher BMI and larger waist circumference — despite normal to decreased food intake and comparable physical activity. The comparison group is chosen well: patients with idiopathic hypersomnia, who share the sleepiness but have normal orexin, do not show it. Gain of function goes the other way: transgenic orexin overexpression confers resistance to high-fat-diet-induced obesity by promoting energy expenditure and reducing consumption — and the phenotype depends on an intact OX2R gene, which the authors note proves physiological signaling rather than a transgene artefact. Another, in the same knockout, states: we did not detect abnormalities in brown adipose tissues of orexin-deficient mice. The weight phenotype is not in dispute; the brown-fat explanation is. doi 10.3389/fendo.2020.00145
It reduces Curbs appetite.
10.3389/fphar.2013.00165 — The aging outcome lists the thirteen hallmarks themselves, each mapped to its pathway and labeled with its hallmark number. (from the reviews of this outcome). Verbatim: “Together, our data suggest that OX1R activity in the VTA facilitates food intake, potentially by counteracting postingestive negative feedback that would normally suppress feeding later in a meal”. doi 10.3389/fphar.2013.00165 · PMC5142223
It increases Alertness.
10.3389/fendo.2013.00018 — Dense orexin-immunoreactive fibers in the LC were found to have a significant excitatory effect in vitro and were demonstrated to have an essential role in mediating transitions of sleep to wake in vivo. doi 10.3389/fendo.2013.00018 · PMC7873441
Blends that modulate it
Each blend page names this pathway and carries the study behind its claim.
See it on the map
Open the causal map to follow this pathway upstream and downstream, arrow by arrow, each with its study.