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

ABSTRACT

Here we describe a novel group of basal forebrain (BF) neurons expressing neuronal 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, 5-6 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 (inactive) period increased the amount of wakefulness and the latency to sleep for 2-3 hr, due to an increase in long wake bouts and short NREM sleep bouts. Non-REM slow-wave (0-1.5 Hz) and sigma (9-15 Hz) 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.

SIGNIFICANCE STATEMENT

We characterize a group of basal forebrain (BF) neurons in the mouse expressing neuronal PAS domain 1 (Npas1), a developmental transcription factor linked to neuropsychiatric disorders. BF Npas1 ⁺ neurons are a major subset of GABAergic neurons distinct and more numerous than cholinergic, parvalbumin or glutamate neurons. BF Npas1 ⁺ neurons target brain areas involved in arousal, motivation and olfaction. Activation of BF Npas1 ⁺ neurons in the light (inactive) period increased wakefulness and the latency to sleep due to increased long wake bouts. Non-REM sleep slow waves and spindles were reduced reminiscent of findings in several neuropsychiatric disorders. Identification of this major subpopulation of BF GABAergic wake-promoting neurons will allow studies of their role in insomnia, dementia and other conditions involving BF.

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