RESPIRATORY NUCLEI SHARE SYNAPTIC CONNECTIVITY WITH PONTINE RETICULARREGIONS REGULATING REM-SLEEP

Injection of cholinomimetics into the medial pontine reticular formati on (mPRF) of intact, unanesthetized cat causes a rapid eye movement (R EM) sleep-like state and respiratory depression. The mPRF contains no concentrations of respiratory neurons, and this study examined the hyp othesis that respiratory depression evoked from the mPRF is synaptical ly mediated. The mPRF of conscious cats was injected with bethanechol to define an mPRF zone causing state-dependent respiratory depression. Bethanechol caused a 361% increase in the REM sleep-like state and a 37% decrease in minute ventilation. Additional cats were injected with the retrograde fluorescent tracers True Blue and either Fluoro-Gold o r Diamidino Yellow aimed for the cholinoceptive mPRF or for the pontin e respiratory group (PRG). After mPRF dye injection, 1) labeling was o bserved in the PRG, dorsal respiratory group (DRG), and ventral respir atory group (VRG); and 2) double-labeled cells were observed in the VR G and PRG. Dye injections into the PRG produced contralateral and ipsi lateral fluorescent labeling of the mPRF, DRG, and VRG. Thus cholinoce ptive regions of the mPRF involved in REM sleep generation have recipr ocal monosynaptic connections with the PRG and receive monosynaptic pr ojections from the DRG and VRG.