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Developmental changes in the orexin 2 receptor mRNA in hypoglossal motoneurons
Denys V Volgin1, Mohammed Saghir, Leszek Kubin
1Department of Animal Biology, School of Veterinary Medicine and Center for Sleep and Respiratory Neurobiology, University of Pennsylvania, 3800 Spruce Street, Philadelphia, PA 19104-6046, USA.
Abstract:
Hypothalamic orexin-containing neurons project to many CNS targets, including motoneurons. We assessed developmental changes in the expression of the orexin type 2 receptor (ORX2r) mRNA in hypoglossal (XII) motoneurons. Identified motoneurons were dissociated from 4- to 33-day-old rats and subjected to single-cell reverse transcription and PCR; nearly all contained the ORX2r mRNA. In 40 motoneurons studied using semi-nested PCR, and in another 39 subjected to quantitative, real-time PCR, the number of reverse-transcribed mRNA copies per cell was significantly higher around day 20 postnatally than at any other age. Thus, ORX may postsynaptically excite XII motoneurons, with the ORX2r mRNA production increased during the critical period for development of the rapid eye movement sleep and its disorder narcolepsy/cataplexy.
Insights
Orexin type 2 receptor mRNA is highly expressed in rat hypoglossal motoneurons around postnatal day 20. This suggests orexin may excite these neurons during critical sleep development periods.
Area of Science:
- Neuroscience
- Molecular Biology
Background:
- Hypothalamic orexin neurons project to various central nervous system targets, including motoneurons.
- Orexin signaling is crucial for regulating sleep-wake cycles and has been implicated in narcolepsy.
Purpose of the Study:
- To investigate developmental changes in orexin type 2 receptor (ORX2r) mRNA expression in hypoglossal (XII) motoneurons.
- To determine the temporal expression pattern of ORX2r mRNA during postnatal development.
Main Methods:
- Dissociation of hypoglossal motoneurons from rats aged 4 to 33 days.
- Single-cell reverse transcription and polymerase chain reaction (PCR) to detect ORX2r mRNA.
- Semi-nested PCR and quantitative, real-time PCR to quantify ORX2r mRNA levels per cell.
Main Results:
- Nearly all studied hypoglossal motoneurons expressed ORX2r mRNA throughout the developmental period.
- A significant peak in ORX2r mRNA copies per cell was observed around postnatal day 20.
- ORX2r mRNA levels were significantly higher at postnatal day 20 compared to other ages studied.
Conclusions:
- Orexin likely exerts a postsynaptic excitatory effect on hypoglossal motoneurons.
- Increased ORX2r mRNA production during the critical developmental period may be linked to the development of rapid eye movement sleep and narcolepsy/cataplexy.