Differential Role of Pontomedullary Glutamatergic Neuronal Populations in Sleep-Wake Control

Parafacial zone (PZ) GABAergic neurons play a major role in slow-wave-sleep (SWS), also called non-rapid eye movement (NREM) sleep. The PZ also contains glutamatergic neurons expressing the vesicular transporter for glutamate, isoform 2 (Vglut2). We hypothesized that PZ Vglut2-expressing (PZ(Vglut2)) neurons are also involved in sleep control, playing a synergistic role with PZ GABAergic neurons. To test this hypothesis, we specifically activated PZ(Vglut2) neurons using the excitatory chemogenetic receptor hM3Dq. Anatomical inspection of the injection sites revealed hM3Dq transfection in PZ, parabrachial nucleus (PB), sublaterodorsal nucleus (SLD) or various combinations of these three brain areas. Consistent with the known wake- and REM sleep-promoting role of PB and SLD, respectively, chemogenetic activation of PB(Vglut2) or SLD(Vglut2) resulted in wake or REM sleep enhancement. Chemogenetic activation of PZ(Vglut2) neurons did not affect sleep-wake phenotype during the mouse active period but increased wakefulness and REM sleep, similar to PB(Vglut2) and SLD(Vglut2) activation, during the rest period. To definitively confirm the role of PZ(Vglut2) neurons, we used a specific marker for PZ(Vglut2) neurons, Phox2B. Chemogenetic activation of PZ(Phox2B) neurons did not affect sleep-wake phenotype, indicating that PZ glutamatergic neurons are not sufficient to affect sleep-wake cycle. These results indicate that PZ glutamatergic neurons are not involved in sleep-wake control.