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Postnatal development of orexin/hypocretin in rats
1Department of Physiology, School of Medicine, University of Occupational and Environmental Health, 1-1 Iseigaoka, Yahatanishi-ku, Kitakyushu 807-8555, Japan.
Brain Research. Molecular Brain Research
|July 13, 2000
Summary
This study reveals that orexin (hypocretin) system development in rats is influenced by leptin, with significant increases observed post-weaning. These findings link orexin system maturation to feeding and sleep-wake states.
Area of Science:
- Neuroscience
- Developmental Biology
- Endocrinology
Background:
- The orexin/hypocretin system plays a crucial role in regulating sleep-wake states and appetite.
- Understanding the developmental trajectory of this system is essential for comprehending its mature functions.
Purpose of the Study:
- To investigate the developmental changes of orexins and their receptors (OX1R, OX2R) in the rat hypothalamus from birth to 10 weeks.
- To examine the impact of milk deprivation and leptin administration on hypothalamic prepro-orexin mRNA levels in developing rats.
Main Methods:
- In situ hybridization histochemistry was used to analyze prepro-orexin, OX1R, and OX2R mRNA expression.
- Immunohistochemistry was employed to detect orexin-A and orexin-B peptide levels.
- The effects of milk deprivation and leptin administration on prepro-orexin mRNA were assessed in rat pups.
Main Results:
- Prepro-orexin mRNA and orexin peptides were detected after postnatal day 15, with a significant increase between days 15-20.
- OX1R and OX2R mRNA expression gradually increased throughout the postnatal period.
- While milk deprivation had no effect, leptin administration from days 0-3 significantly increased prepro-orexin mRNA on days 5 and 10.
Conclusions:
- The development of the orexin system in rats is characterized by a significant increase in expression after weaning.
- Leptin administration can precociously stimulate orexin system development.
- Orexin system maturation is likely associated with developmental changes including increased leptin levels, weaning, and the establishment of feeding and sleep-wake patterns.