Neuronal PAS domain 1 identifies a major subpopulation of wakefulness-promoting GABAergic neurons in the basal forebrain

Here, we describe a group of basal forebrain (BF) neurons expressing neuronal Per-Arnt-Sim (PAS) domain 1 (Npas1), a developmental transcription factor linked to neuropsychiatric disorders. Immunohistochemical staining in Npas1-cre-2A-TdTomato mice revealed BF Npas1⁺ neurons are distinct from well-studied parvalbumin or cholinergic neurons. Npas1 staining in GAD67-GFP knock-in mice confirmed that the vast majority of Npas1⁺ neurons are GABAergic, with minimal colocalization with glutamatergic neurons in vGlut1-cre-tdTomato or vGlut2-cre-tdTomato mice. The density of Npas1⁺ neurons was high, five to six times that of neighboring cholinergic, parvalbumin, or glutamatergic neurons. Anterograde tracing identified prominent projections of BF Npas1⁺ neurons to brain regions involved in sleep–wake control, motivated behaviors, and olfaction such as the lateral hypothalamus, lateral habenula, nucleus accumbens shell, ventral tegmental area, and olfactory bulb. Chemogenetic activation of BF Npas1⁺ neurons in the light period increased the amount of wakefulness and the latency to sleep for 2 to 3 h, due to an increase in long wake bouts and short NREM sleep bouts. NREM slow-wave and sigma power, as well as sleep spindle density, amplitude, and duration, were reduced, reminiscent of findings in several neuropsychiatric disorders. Together with previous findings implicating BF Npas1⁺ neurons in stress responsiveness, the anatomical projections of BF Npas1⁺ neurons and the effect of activating them suggest a possible role for BF Npas1⁺ neurons in motivationally driven wakefulness and stress-induced insomnia. Identification of this major subpopulation of BF GABAergic neurons will facilitate studies of their role in sleep disorders, dementia, and other neuropsychiatric conditions involving BF.