GABA neurons in the ventral tegmental area regulate non-rapid eye movement sleep in mice

Abstract

1The daily sleep/wakefulness cycle is regulated by coordinated interactions between 2 sleep-and wakefulness-regulating neural circuitry. However, the detailed neural circuitry 3 mediating sleep is far from understood. Here, we found that glutamic acid 4 decarboxylase 67 (Gad67)-positive GABAergic neurons in the ventral tegmental area 5 (VTAGad67+) are a key regulator of non-rapid eye movement (NREM) sleep in mice. 6 VTAGad67+ neurons project to multiple brain areas implicated in sleep/wakefulness 7 regulation such as the lateral hypothalamus (LH) and dorsal raphe nucleus.8 Chemogenetic activation of VTAGad67+ neurons promoted NREM sleep with higher delta 9 power whereas optogenetic inhibition of these neurons induced prompt arousal from 10 NREM sleep under highly somnolescent conditions, but not during REM sleep. In vivo 11 fiber photometry recordings revealed that VTAGad67+ neurons showed the highest 12 population activity in NREM sleep and the lowest activity in REM sleep. Acute brain 13 slice electrophysiology combined with optogenetics revealed that VTAGad67+ neurons 14 directly innervate and inhibit wake-promoting orexin/hypocretin neurons in the LH by 15 releasing GABA. Taken together, we reveal that VTAGad67+ neurons play a crucial role in 16 the regulation of NREM sleep.17 18

Dopamine neurons in the ventral periaqueductal gray modulate isoflurane anesthesia in rats

“…15,20 Recently, chemogenetic activation of GABA neurons in the VTA promoted NREM sleep with higher delta power in mice. 23 In addition, selective ablation or suppression of GABAergic neurons in VMP where includes VTA and rostomedial tegmental nucleus increased wakefulness through disinhibiting dopaminergic systems, while special activation of VMP GABAergic neurons strongly increased SWS and drastically decreased wakefulness. 24 We speculated that the vPAG-DA neurons may be suppressed by inhibiting extrinsic GABAergic activity during isoflurane anesthesia, and microinjection of the GABA A R antagonist might disinhibit the inhibition of vPAG-DA neurons, implying that GABA receptors involved in regulating the isoflurane-induced anesthesia.…”

Arousal State-Dependent Alterations in VTA-GABAergic Neuronal Activity

“…When VTA-GABAergic neural activity was monitored using fiber photometry, they observed high calcium fluorescence during wakefulness and REM sleep, similar to our findings. In contrast, Chowdhury and colleagues recently observed that GAD67+ GABAergic neurons in the VTA are mostly active during NREM sleep (Chowdhury et al, 2019).…”

“…The different studies (Yu et al, Chowdhury et al and Eban-Rothschild et al) also used different viral constructs and/or promoters that may have influenced the viral tropism and expression levels of GCaMP in the VTA. It is also important to note that while Chowdhury and colleagues reported higher population activity in VTA GAD67+ neurons during NREM sleep compared to wakefulness and REM sleep, examination of their data suggests an increase in population activity immediately following sleepto-wake transitions, and higher transient rates during wakefulness and REM sleep compared to NREM sleep (Chowdhury et al, 2019). Broadly, GABAergic neurons are highly heterogeneous across the brain (e.g., see (Jones, 2017)), and the use of bulk population activity recordings may mask ensemble differences in activity patterns.…”

“…Moreover, it is still unclear whether activity in VTA-GABAergic neurons precedes or lags behind arousal state transitions, how population activity in the VTA is related to different components of the cortical EEG and how VTA-GABAergic population dynamics relate to that of co-mingled dopaminergic neurons. A few recent studies have shed some light onto these questions, demonstrating that VTA-GABAergic neurons bidirectionally regulate wakefulness in part via their projections to the lateral hypothalamus (LH) (Takata et al, 2018;Chowdhury et al, 2019;Yu et al, 2019b).…”

“…However, there are some critical discrepancies between these studies, as one suggests that VTA-GABAergic neurons are predominantly wake and REM sleep active (Yu et al, 2019), while the other provides evidence that these neurons fire mostly during NREM sleep (Chowdhury et al, 2019). Therefore, the exact phenotype of VTA-GABAergic neurons across arousal states remains unclear.…”