Activity of GABA neurons in the zona incerta and ventral lateral periaqueductal grey is biased towards sleep

Transcriptomic and spatial GABAergic neuron subtypes in zona incerta mediate distinct innate behaviors

Understanding the anatomical connection and behaviors of transcriptomic neuron subtypes is critical to delineating cell type-specific functions in the brain. Here we integrated single-nucleus transcriptomic sequencing, in vivo circuit mapping, optogenetic and chemogenetic approaches to dissect the molecular identity and function of heterogeneous GABAergic neuron populations in the zona incerta (ZI) in mice, a region involved in modulating various behaviors. By microdissecting ZI for transcriptomic and spatial gene expression analyses, our results revealed two non-overlapping Ecel1- and Pde11a-expressing GABAergic neurons with dominant expression in the rostral and medial zona incerta (ZIrEcel1 and ZImPde11a), respectively. The GABAergic projection from ZIrEcel1 to periaqueductal gray mediates self-grooming, while the GABAergic projection from ZImPde11a to the oral part of pontine reticular formation promotes transition from sleep to wakefulness. Together, our results revealed the molecular markers, spatial organization and specific neuronal circuits of two discrete GABAergic projection neuron populations in segregated subregions of the ZI that mediate distinct innate behaviors, advancing our understanding of the functional organization of the brain.

Abnormal iron metabolism in the zona incerta in Parkinson's disease mice

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra (SN) and abnormal iron metabolism. While most of the current studies have focused on nigral iron deposition, there is still limited research into the role of iron in other brain regions. The zona incerta (ZI) is a heterogeneous subthalamic region and has extensive connections with the basal ganglia nucleus. Clinically, the ZI has been recognized as a new therapeutic target for PD. Deep brain stimulation of the ZI has been reported to relieve motor symptoms and experimental heat pain in patients with PD. The aim of the present study is to evaluate changes in iron levels in the ZI. Two neurotoxins, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA), were used to prepare PD mice. By immunostaining, we first measured the success of MPTP or 6-OHDA injury. We found that the expressions of tyrosine hydroxylase were decreased after MPTP or 6-OHDA treatment. Secondly, we observed the changes of iron metabolism using Perls' iron staining and western blots. Our results showed that the numbers of iron-positive cells were significantly increased in the SN and ZI of MPTP/6-OHDA-treated mice. Moreover, the expression levels of ferritin and divalent metal transporter 1 (DMT1) in the ZI were also increased in the PD group. Glutathione peroxidase 4 (GPX4), a marker of ferroptosis, was also detected. Western blots revealed that MPTP significantly down-regulated the level of GPX4 in the ZI. As glial cells activation and neuroinflammation play important roles in the ion deposition, we finally investigated the microglial and astrocyte activation and inflammatory factors. These results suggested increased iron levels and inflammation may be present in the ZI in PD mice.

The zona incerta system: Involvement in Parkinson's disease

Parkinson's disease (PD) is characterized by degeneration of the nigrostriatal dopamine system, resulting in progressive motor and nonmotor symptoms. Although most studies have focused on the basal ganglia network, recent evidence suggests that the zona incerta (ZI), a subthalamic structure composed of 4 neurochemically defined regions, is emerging as a therapeutic target in PD. This review summarizes the clinical and animal studies that indicate the importance of ZI in PD. Human clinical studies have shown that subthalamotomy or deep brain stimulation (DBS) of the ZI alleviates muscle rigidity, bradykinesia, tremors and speech dysfunction in patients with PD. Researchers have also studied the impact of DBS of the ZI on nonmotor signs such as pain, anxiety, and depression. Animal studies combining optogenetics, chemogenetics, behavioral assays, and neural activity recordings reveal the functional roles of ZI GABAergic and glutamatergic neurons in locomotion, gait, and coordination of the symptoms of PD, all of which are discussed in this review. Controversies and possible future studies are also discussed.

Acute Ongoing Nociception Delays Recovery of Consciousness from Sevoflurane Anesthesia via a Midbrain Circuit

Although anesthesia provides favorable conditions for surgical procedures, recent studies have revealed that the brain remains active in processing noxious signals even during anesthesia. However, whether and how these responses affect the anesthesia effect remains unclear. The ventrolateral periaqueductal gray (vlPAG), a crucial hub for pain regulation, also plays an essential role in controlling general anesthesia. Hence, it was hypothesized that the vlPAG may be involved in the regulation of general anesthesia by noxious stimuli. Here, we found that acute noxious stimuli, including capsaicin-induced inflammatory pain, acetic acid-induced visceral pain, and incision-induced surgical pain, significantly delayed recovery from sevoflurane anesthesia in male mice, whereas this effect was absent in the spared nerve injury-induced chronic pain. Pretreatment with peripheral analgesics could prevent the delayed recovery induced by acute nociception. Furthermore, we found that acute noxious stimuli, induced by the injection of capsaicin under sevoflurane anesthesia, increased c-Fos expression and activity in the GABAergic neurons of the ventrolateral periaqueductal gray. Specific reactivation of capsaicin-activated vlPAGGABA neurons mimicked the effect of capsaicin and its chemogenetic inhibition prevented the delayed recovery from anesthesia induced by capsaicin. Finally, we revealed that the vlPAGGABA neurons regulated the recovery from anesthesia through the inhibition of ventral tegmental area dopaminergic neuronal activity, thus decreasing dopamine (DA) release and activation of DA D1-like receptors in the brain. These findings reveal a novel, cell- and circuit-based mechanism for regulating anesthesia recovery by nociception, and it is important to provide new insights for guiding the management of the anesthesia recovery period.

Most dynorphin neurons in the zona incerta-perifornical area are active in waking relative to non-rapid-eye movement and rapid-eye movement sleep

Dynorphin is an endogenous opiate localized in many brain regions and spinal cord, but the activity of dynorphin neurons during sleep is unknown. Dynorphin is an inhibitory neuropeptide that is coreleased with orexin, an excitatory neuropeptide. We used microendoscopy to test the hypothesis that, like orexin, the dynorphin neurons are wake-active. Dynorphin-cre mice (n = 3) were administered rAAV8-Ef1a-Con/Foff 2.0-GCaMP6M into the zona incerta-perifornical area, implanted with a GRIN lens (gradient reflective index), and electrodes to the skull that recorded sleep. One month later, a miniscope imaged calcium fluorescence in dynorphin neurons during multiple bouts of wake, non-rapid-eye movement (NREM), and rapid-eye movement (REM) sleep. Unbiased data analysis identified changes in calcium fluorescence in 64 dynorphin neurons. Most of the dynorphin neurons (72%) had the highest fluorescence during bouts of active and quiet waking compared to NREM or REM sleep; a subset (20%) were REM-max. Our results are consistent with the emerging evidence that the activity of orexin neurons can be classified as wake-max or REM-max. Since the two neuropeptides are coexpressed and coreleased, we suggest that dynorphin-cre-driven calcium sensors could increase understanding of the role of this endogenous opiate in pain and sleep.

Neural Control of REM Sleep and Motor Atonia: Current Perspectives

PURPOSE OF REVIEW

Since the formal discovery of rapid eye movement (REM) sleep in 1953, we have gained a vast amount of knowledge regarding the specific populations of neurons, their connections, and synaptic mechanisms regulating this stage of sleep and its accompanying features. This article discusses REM sleep circuits and their dysfunction, specifically emphasizing recent studies using conditional genetic tools.

RECENT FINDINGS

Sublaterodorsal nucleus (SLD) in the dorsolateral pons, especially the glutamatergic subpopulation in this region (SLDGlut), are shown to be indispensable for REM sleep. These neurons appear to be single REM generators in the rodent brain and may initiate and orchestrate all REM sleep events, including cortical and hippocampal activation and muscle atonia through distinct pathways. However, several cell groups in the brainstem and hypothalamus may influence SLDGlut neuron activity, thereby modulating REM sleep timing, amounts, and architecture. Damage to SLDGlut neurons or their projections involved in muscle atonia leads to REM behavior disorder, whereas the abnormal activation of this pathway during wakefulness may underlie cataplexy in narcolepsy. Despite some opposing views, it has become evident that SLDGlut neurons are the sole generators of REM sleep and its associated characteristics. Further research should prioritize a deeper understanding of their cellular, synaptic, and molecular properties, as well as the mechanisms that trigger their activation during cataplexy and make them susceptible in RBD.