For their participation in energy homeostasis, orexins (also called hypocretins) were first identified as neuropeptides. Their involvement in sleep-wake cycle regulation and appetite signaling pathways was demonstrated by subsequent research.
Neurobiology of the Orexin System
Approximately 10,000-20,000 orexin-producing neurons are contained within the human brain. Despite this relatively small population, with widely distributed receptor populations, throughout the central nervous system these neurons project extensively.
In various physiological processes, orexin’s involvement has been documented by research in animal models. Under different experimental conditions, alterations in orexin signaling have been observed in laboratory models.
Orexin and Energy Expenditure
In brown adipose tissue (BAT) formation, orexin participates. Via mitochondrial uncoupling mechanisms through non-shivering thermogenesis, BAT generates heat. Using various animal models, orexin’s role in this process is investigated by research.
On metabolic pathways in sheep models, their relative effects have been examined by studies comparing orexin to leptin (a hormone involved in satiety signaling). For their metabolic phenotypes, mouse models with genetic alterations affecting orexin production have been studied.
GHRH Analogs
As research tools, growth hormone-releasing hormone (GHRH) analogs like sermorelin have been investigated. How these compounds interact with the growth hormone axis and potentially influence orexin neuron activity in animal models is examined by studies.
References:
- Álvarez-Crespo, M., et al. (2013). Orexin system interactions. Endocrinology, 154(10), 3589-3598.
- Kirsz, K., et al. (2014). Hormone interactions in ovine models. Domest Anim Endocrinol, 48, 69-76.
- Sellayah, D., et al. (2011). Orexin in adipose tissue. Cell Metab, 14(4), 478-490.
- Shepherd, B. S., et al. (2007). Growth hormone secretagogue actions. Comp Biochem Physiol A, 146(3), 390-399.
