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Orexin actions in hypothalamic paraventricular nucleus: physiological consequences and cellular correlates.
Willis K Samson1, Meghan M Taylor, Matthew Follwell
1Department of Pharmacological and Physiological Sciences, Saint Louis University School of Medicine, 1402 South Grand Boulevard, St. Louis, MO 63104, USA. samsonwk@slu.edu
Regulatory Peptides
|February 7, 2002
Summary
Orexin A administration in rats significantly increased adrenocorticotropin (ACTH) levels, suggesting a role for orexin in regulating the stress response via the hypothalamo-pituitary-adrenal (HPA) axis.
Area of Science:
- Neuroendocrinology
- Neurobiology
- Stress Physiology
Background:
- Orexinergic neurons in the hypothalamus project to stress-responsive neuroendocrine centers.
- These projections suggest orexin's potential involvement in regulating adrenocorticotropin (ACTH) release.
Purpose of the Study:
- To investigate if exogenous orexin A affects ACTH release in the brain.
- To identify the paraventricular nucleus (PVN) as a potential site of action for orexin A.
Main Methods:
- Cerebroventricular administration of orexin A in conscious male rats.
- Measurement of circulating ACTH levels post-infusion.
- CRH-antagonist pretreatment to assess HPA axis activation.
- Electrophysiological recordings in hypothalamic slice preparations.
Main Results:
- Orexin A caused a dose-dependent increase in ACTH levels.
- CRH-antagonist blocked orexin A-induced HPA axis activation.
- Orexin A induced neuronal depolarization and increased firing in PVN neurons.
Conclusions:
- Orexin A acts within the brain to stimulate ACTH release.
- The paraventricular nucleus (PVN) is a key site where orexin influences the stress response.
- Endogenous orexin may play a role in the hypothalamic regulation of stress hormone secretion.