0143 CARBACHOL INHIBITS GLUTAMATERGIC INPUT TO MOUSE HYPOGLOSSAL MOTOR NEURONS - A MECHANISM FOR REM SLEEP SUPPRESSION OF GENIOGLOSSUS ACTIVITY

Abstract

In REM sleep, the genioglossus (GG) muscle undergoes a dramatic suppression of activity. A current hypothesis is that the loss of GG activity during REM sleep is mediated by a combination of 1) monoaminergic disfacilitation and 2) a cholinergic inhibition of hypoglossal motor neurons. Strikingly, blockade of cholinergic receptors in the hypoglossal motor nucleus fully restores REM sleep tonic and inspiratory-modulated components of GG activity (Grace et al., 2013), suggesting that the cholinergic signal is largely responsible for the REM sleep suppression of GG activity. Respiratory rhythm generator neurons of the pre-Bötzinger complex drive the activation of hypoglossal motor neurons through glutamatergic premotor neurons in the parahypoglossal region (PH). In the current study, we investigate how cholinergic signaling affects the PH glutamatergic input to hypoglossal motor neurons. We stereotaxically injected the PH region of vGluT2-cre mice with a cre-dependent AAV-ChR2-mCherry to expressed channelrhodopsin2 (ChR2) in PH glutamatergic premotor neurons. We then performed whole-cell recordings in hypoglossal neurons while photostimulating PH glutamatergic inputs expressing ChR2. Photostimulation of the glutamatergic PH input evoked AMPA-mediated EPSCs in hypoglossal motor neurons. These photoevoked EPSCs were maintained in TTX, indicating direct connectivity between stimulated terminals and recorded hypoglossal motoneurons. Bath application of carbachol strongly inhibited the PH glutamatergic excitation of hypoglossal neurons via muscarinic receptors. The effect of carbachol on photoevoked EPSCs was maintained when 1) we blocked postsynaptic G-mediated effects by adding GDP-β-S in the recording pipette and 2) when we blocked action potential mediated transmission by adding TTX in the extracellular bath solution. These results indicate that carbachol inhibits PH input to hypoglossal motoneurons through a presynaptic mechanism. Our results provide a possible mechanism for cholinergic inhibition of the hypoglossal motor neurons in REM sleep. We propose that the cholinergic presynaptic suppression of the excitatory drive from the PH premotor neurons can be responsible for the reduction in activity of hypoglossal motor neurons in REM sleep. P01HL095491.