Developmental changes in the orexin 2 receptor mRNA in hypoglossal motoneurons.

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.