Regulation of wakefulness by neurotensin neurons in the lateral hypothalamus

The lateral hypothalamic region (LH) has been identified as a key region for arousal regulation, yet the specific cell types and underlying mechanisms are not fully understood. While neurons expressing orexins (OX) are considered the primary wake-promoting population in the LH, their loss does not reduce daily wake levels, suggesting the presence of additional wake-promoting populations. In this regard, we recently discovered that a non-OX cell group in the LH, marked by the expression of neurotensin (Nts), could powerfully drive wakefulness. Activation of these Nts^LH neurons elicits rapid arousal from non-rapid eye movement (NREM) sleep and produces uninterrupted wakefulness for several hours in mice. However, it remains unknown if these neurons are necessary for spontaneous wakefulness and what their precise role is in the initiation and maintenance of this state. To address these questions, we first examined the activity dynamics of the Nts^LH population across sleep-wake behavior using fiber photometry. We find that Nts^LH neurons are more active during wakefulness, and their activity increases concurrently with, but does not precede, wake-onset. We then selectively destroyed the Nts^LH neurons using a diphtheria-toxin-based conditional ablation method, which significantly reduced wake amounts and mean duration of wake bouts and increased the EEG delta power during wakefulness. These findings demonstrate a crucial role for Nts^LH neurons in maintaining normal arousal levels, and their loss may be associated with chronic sleepiness in mice.