Genetic Activation, Inactivation, and Deletion Reveal a Limited And Nuanced Role for Somatostatin-Containing Basal Forebrain Neurons in Behavioral State Control

Recent studies have identified an especially important role for basal forebrain GABAergic (BFVGAT) neurons in the regulation of behavioral waking and fast cortical rhythms associated with cognition. However, BFVGATneurons comprise several neurochemically and anatomically distinct subpopulations, including parvalbumin-containing BFVGATneurons and somatostatin-containing BFVGATneurons (BFSOMneurons), and it was recently reported that optogenetic activation of BFSOMneurons increases the probability of a wakefulness to non-rapid-eye movement (NREM) sleep transition when stimulated during the rest period of the animal. This finding was unexpected given that most BFSOMneurons are not NREM sleep active and that central administration of the synthetic somatostatin analog, octreotide, suppresses NREM sleep or increases REM sleep. Here we used a combination of genetically driven chemogenetic and optogenetic activation, chemogenetic inhibition, and ablation approaches to further explore thein vivorole of BFSOMneurons in arousal control. Our findings indicate that acute activation or inhibition of BFSOMneurons is neither wakefulness nor NREM sleep promoting and is without significant effect on the EEG, and that chronic loss of these neurons is without effect on total 24 h sleep amounts, although a small but significant increase in waking was observed in the lesioned mice during the early active period. Ourin vitrocell recordings further reveal electrophysiological heterogeneity in BFSOMneurons, specifically suggesting at least two distinct subpopulations. Together, our data support the more nuanced view that BFSOMneurons are electrically heterogeneous and are not NREM sleep or wake promoting per se, but may exert, in particular during the early active period, a modest inhibitory influence on arousal circuitry.SIGNIFICANCE STATEMENTThe cellular basal forebrain (BF) is a highly complex area of the brain that is implicated in a wide range of higher-level neurobiological processes, including regulating and maintaining normal levels of electrocortical and behavioral arousal. The respectivein vivoroles of BF cell populations and their neurotransmitter systems in the regulation of electrocortical and behavioral arousal remains incompletely understood. Here we seek to define the neurobiological contribution of GABAergic somatostatin-containing BF neurons to arousal control. Understanding the respective contribution of BF cell populations to arousal control may provide critical insight into the pathogenesis of a host of neuropsychiatric and neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, schizophrenia, and the cognitive impairments of normal aging.