oreksiinijärjestelmä

The oreksiinijärjestelmä, or orexin system, is a neuropeptide signaling pathway in the mammalian brain that plays a central role in regulating wakefulness, appetite, and energy balance. Orexins, also called hypocretins, are produced by neurons in the lateral and dorsomedial hypothalamus and are released into the cerebrospinal fluid and synaptic clefts. The peptides exist as two isoforms, orexin‑A (hypocretin‑1) and orexin‑B (hypocretin‑2), which bind to two G‑protein‑coupled receptors, OX1R and OX2R. These receptors are widely distributed in the central nervous system and in peripheral tissues, enabling orexins to influence a variety of physiological processes.

Functionally, the oreksiinijärjestelmä enhances arousal and vigilance through stimulation of cortical and subcortical arousal centers, including the locus coeruleus, raphe nuclei, and noradrenergic fibers. It also modulates feeding behavior by acting on hypothalamic nuclei such as the arcuate nucleus, where orexin neurons stimulate appetite through interaction with neuropeptide Y and other orexigenic pathways. Additionally, the system contributes to thermoregulation, reward pathways, and cardiovascular regulation. Disruption of orexin signaling can lead to narcolepsy, characterized by excessive daytime sleepiness and cataplexy, demonstrating the system’s importance in maintaining sleep–wake homeostasis.

In clinical research, orexin receptor antagonists have been developed as treatments for insomnia, exploiting the ability to reduce wakefulness-promoting signals. Conversely, enhancing orexin activity or stabilizing orexin neurons holds promise for treating conditions such as weight loss, cachexia, and certain mood disorders. The oreksiinijärjestelmä remains a focus of neurobiological investigations into the interplay between sleep, metabolism, and neuropsychiatric function.