Abstract

Recent studies have identified an especially important role for basal forebrain GABAergic (BF^VGAT) neurons in the regulation of behavioral waking and fast cortical rhythms associated with cognition. However, BF^VGAT neurons comprise several neurochemically and anatomically distinct sub-populations, including parvalbumin- and somatostatin-containing BF^VGAT neurons (BF^Parv and BF^SOM), and it was recently reported that optogenetic activation of BF^SOM neurons increases the probability of a wakefulness to non-rapid-eye movement (NREM) sleep transition when stimulated during the animal's rest period. This finding was unexpected given that most BF^SOM neurons are not NREM sleep active and that central administration of the synthetic SOM analog, octreotide, suppresses NREM sleep or increases REM sleep. Here we employed a combination of genetically-driven chemogenetic and optogenetic activation, chemogenetic inhibition and ablation approaches to further explore the in vivo role of BF^SOM neurons in arousal control. Our findings indicate that acute activation or inhibition of BF^SOM neurons is neither wakefulness- nor NREM sleep-promoting, is without significant effect on the EEG, and that chronic loss of these neurons is without effect on total 24h sleep amounts, although a small but significant increase in waking was observed in the lesioned mice during the early active period. Our in vitro cell recordings further reveal electrophysiological heterogeneity in BF^SOM neurons, specifically suggesting at least two distinct sub-populations. Taken together our data support the more nuanced view that BF^SOM 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 STATEMENT

The 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 respective in vivo roles 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 somatostanin-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.