Supramammillary glutamate neurons are a key node of the arousal system

Basic and clinical observations suggest that the caudal hypothalamus comprises a key node of the ascending arousal system, but the cell types underlying this are not fully understood. Here we report that glutamate-releasing neurons of the supramammillary region (SuM^vglut2) produce sustained behavioral and EEG arousal when chemogenetically activated. This effect is nearly abolished following selective genetic disruption of glutamate release from SuM^vglut2 neurons. Inhibition of SuM^vglut2 neurons decreases and fragments wake, also suppressing theta and gamma frequency EEG activity. SuM^vglut2 neurons include a subpopulation containing both glutamate and GABA (SuM^vgat/vglut2) and another also expressing nitric oxide synthase (SuM^Nos1/Vglut2). Activation of SuM^vgat/vglut2 neurons produces minimal wake and optogenetic stimulation of SuM^vgat/vglut2 terminals elicits monosynaptic release of both glutamate and GABA onto dentate granule cells. Activation of SuM^Nos1/Vglut2 neurons potently drives wakefulness, whereas inhibition reduces REM sleep theta activity. These results identify SuM^vglut2 neurons as a key node of the wake-sleep regulatory system.