The Peptide Whose Absence Defines a Disease
Narcolepsy with cataplexy — the classic autoimmune-mediated narcolepsy — is characterized by loss of orexin-producing neurons in the lateral hypothalamus. The absence of orexin signaling is literally the disease. This makes orexin-A one of the rare research peptides with a definitive clinical correlate for its loss-of-function state.
The research-grade peptide is available as Orexin-A 5mg.
Two Discoveries, Two Names
Orexin-A and Hypocretin-1 are the same peptide. In 1998, two research groups independently discovered the compound and published nearly simultaneously:
- Sakurai et al.: Named it "orexin" (Greek *orexis*, appetite) based on initial feeding-behavior observations
- de Lecea et al.: Named it "hypocretin" (hypothalamic + secretin-like) based on sequence homology
Both names persist in the literature. Orexin is more common in metabolic and pharmacological research; hypocretin dominates sleep biology.
Structure: A 33-Amino-Acid Peptide
Orexin-A has two intrachain disulfide bonds and N-terminal pyroglutamation — modifications that contribute to its stability and receptor affinity. It is produced from the preproorexin precursor alongside orexin-B (28 AA), though the two peptides have somewhat different receptor preferences.
Receptor Pharmacology
The orexin system has two GPCR receptors:
| Receptor | Affinity for Orexin-A | Affinity for Orexin-B |
|---|---|---|
| OX1R (HCRTR1) | High | Lower (~10× less) |
| OX2R (HCRTR2) | High | High |
Orexin-A binds both receptors with similar affinity — making it the "pan-orexin" research tool compared to orexin-B's OX2R preference.
Primary Research Functions
Wakefulness and arousal: Orexin neurons in the lateral hypothalamus project widely — to monoaminergic nuclei (locus coeruleus, raphe, ventral tegmental area) and to the basal forebrain cholinergic system. Activation of these targets maintains cortical arousal.
Feeding and energy balance: Orexin neurons sense glucose and leptin signals, producing integrated output that couples feeding drive to arousal state.
Reward and motivation: OX1R signaling in the VTA modulates dopaminergic reward pathways, linking the orexin system to motivation research.
Research Applications
- Sleep biology: Narcolepsy models, circadian research
- Neuropharmacology: Dual orexin receptor antagonists (DORAs) are a major drug development area; research agonists provide the reverse pharmacology
- Metabolic research: Feeding-arousal integration
- Addiction research: OX1R role in drug-seeking behavior
Handling
Lyophilized orexin-A requires careful handling — the disulfide bonds are sensitive to reducing conditions. Standard bacteriostatic water reconstitution is appropriate; avoid DTT or mercaptoethanol-containing buffers. >98% HPLC purity is the research standard.
See Orexin-A 5mg for the research vial.