Anterior cingulate cortex projections to the dorsal medial striatum underlie insomnia associated with chronic pain

Inhibitory gamma-aminobutyric acidergic neurons in the anterior cingulate cortex participate in the comorbidity of pain and emotion

Pain is often comorbid with emotional disorders such as anxiety and depression. Hyperexcitability of the anterior cingulate cortex has been implicated in pain and pain-related negative emotions that arise from impairments in inhibitory gamma-aminobutyric acid neurotransmission. This review primarily aims to outline the main circuitry (including the input and output connectivity) of the anterior cingulate cortex and classification and functions of different gamma-aminobutyric acidergic neurons; it also describes the neurotransmitters/neuromodulators affecting these neurons, their intercommunication with other neurons, and their importance in mental comorbidities associated with chronic pain disorders. Improving understanding on their role in pain-related mental comorbidities may facilitate the development of more effective treatments for these conditions. However, the mechanisms that regulate gamma-aminobutyric acidergic systems remain elusive. It is also unclear as to whether the mechanisms are presynaptic or postsynaptic. Further exploration of the complexities of this system may reveal new pathways for research and drug development.

Structural Imaging Measures of Cortical and Basal Ganglia Morphology in Insomnia

While insomnia disorder is associated with changes in the brain, results vary across studies and levels of severity; no consistent morphometric pattern has yet emerged. Prior large-scale genetic work has implicated specific cortical and subcortical regions in the pathophysiology of insomnia. The aim of the current study is to utilise surface-based morphometry tools to examine these specific regions, thereby offering new insights into the disorder from a genetically informed perspective. This study leveraged archival neuroimaging data from the University of Pittsburgh, analysing 58 individuals with DSM-IV-TR primary insomnia and 67 good sleepers. Using T1-weighted structural MRI scans, harmonised shape analysis protocols were applied for bilateral caudate, putamen and globus pallidus. In addition, cerebellar volumes, as well as anterior cingulate and rostral middle frontal cortical thickness measures were obtained. Linear models were then constructed to assess group differences in all regions, then correlation coefficients between brain values and scores from the Pittsburgh Sleep Quality Index (PSQI) from all participants were calculated. Results revealed individuals with insomnia exhibited significantly greater cortical thinning in anterior cingulate cortex, and inward shape deformation in the head of the right caudate compared to good sleepers. These findings reveal focal neurobiological abnormalities in insomnia that are in line with regions implicated in previous genetic work. The results may hold important implications for future research identifying biomarkers and mechanisms that contribute to the onset and course of insomnia in these areas.

Anterior Cingulate Cortex Contributes to the Hyperlocomotion under Nitrogen Narcosis

Nitrogen narcosis is a neurological syndrome that manifests when humans or animals encounter hyperbaric nitrogen, resulting in a range of motor, emotional, and cognitive abnormalities. The anterior cingulate cortex (ACC) is known for its significant involvement in regulating motivation, cognition, and action. However, its specific contribution to nitrogen narcosis-induced hyperlocomotion and the underlying mechanisms remain poorly understood. Here we report that exposure to hyperbaric nitrogen notably increased the locomotor activity of mice in a pressure-dependent manner. Concurrently, this exposure induced heightened activation among neurons in both the ACC and dorsal medial striatum (DMS). Notably, chemogenetic inhibition of ACC neurons effectively suppressed hyperlocomotion. Conversely, chemogenetic excitation lowered the hyperbaric pressure threshold required to induce hyperlocomotion. Moreover, both chemogenetic inhibition and genetic ablation of activity-dependent neurons within the ACC reduced the hyperlocomotion. Further investigation revealed that ACC neurons project to the DMS, and chemogenetic inhibition of ACC-DMS projections resulted in a reduction in hyperlocomotion. Finally, nitrogen narcosis led to an increase in local field potentials in the theta frequency band and a decrease in the alpha frequency band in both the ACC and DMS. These results collectively suggest that excitatory neurons within the ACC, along with their projections to the DMS, play a pivotal role in regulating the hyperlocomotion induced by exposure to hyperbaric nitrogen.

Distinct Convergent Brain Alterations in Sleep Disorders and Sleep Deprivation: A Meta-Analysis

Importance

Sleep disorders have different etiologies yet share some nocturnal and daytime symptoms, suggesting common neurobiological substrates; healthy individuals undergoing experimental sleep deprivation also report analogous daytime symptoms. However, brain similarities and differences between long-term sleep disorders and short-term sleep deprivation are unclear.

Objective

To investigate the shared and specific neural correlates across sleep disorders and sleep deprivation.

Data Sources

PubMed, Web of Science, Embase, Scopus, and BrainMap were searched up to January 2024 to identify relevant structural and functional neuroimaging articles.

Study Selection

Whole-brain neuroimaging articles reporting voxel-based group differences between patients with different sleep disorders and healthy control participants or between total or partial sleep-deprived and well-rested individuals were included.

Data Extraction and Synthesis

Significant coordinates of group comparisons, their contrast direction (eg, patients < controls), and imaging modality were extracted. For each article, 2 raters independently evaluated eligibility and extracted data. Subsequently, several meta-analyses were performed with the revised activation likelihood estimation algorithm using P < .05 cluster-level familywise error correction.

Main Outcomes and Measures

Transdiagnostic regional brain alterations were identified across sleep disorders and among articles reporting sleep deprivation. Their associated behavioral functions and task-based or task-free connectivity patterns were explored using 2 independent datasets (BrainMap and the enhanced Nathan Kline Institute-Rockland Sample).

Results

A total of 231 articles (140 unique experiments, 3380 unique participants) were retrieved. The analysis across sleep disorders (n = 95 experiments) identified the subgenual anterior cingulate cortex (176 voxels, z score = 4.86), associated with reward, reasoning, and gustation, and the amygdala and hippocampus (130 voxels, z score = 4.00), associated with negative emotion processing, memory, and olfaction. Both clusters had positive functional connectivity with the default mode network. The right thalamus (153 voxels, z score = 5.21) emerged as a consistent regional alteration following sleep deprivation (n = 45 experiments). This cluster was associated with thermoregulation, action, and pain perception and showed positive functional connectivity with subcortical and (pre)motor regions. Subanalyses regarding the direction of alterations demonstrated that the subgenual anterior cingulate cortex exhibited decreased activation, connectivity, and/or volume, while the amygdala and hippocampus cluster and the thalamus cluster demonstrated increased activation, connectivity, and/or volume.

Conclusions and Relevance

Distinct convergent brain abnormalities were observed between long-term sleep disorders (probably reflecting shared symptoms) and short-term sleep deprivation.

Targeting PI3K-mTOR signaling in the anterior cingulate cortex improves emotional behavior, and locomotor activity in rats with bone cancer pain

Objective

To investigate the effects of targeting the PI3K-mTOR signaling pathway in the anterior cingulate cortex (ACC) on pain responses, locomotor activity, and emotional behavior in rats with bone cancer pain.

Methods

Bone cancer pain was induced by implanting Walker 256 cells into the rat. Pain responses were assessed using paw withdrawal threshold and latency measurements, while locomotor activity and negative mood were evaluated through open field and conditioned place aversion tests, respectively.

Results

The results showed that the bone cancer pain model led to allodynia, hyperalgesia, decreased ambulation, and ACC microglial activation. Morphine treatment improved pain responses but did not affect locomotor activity or mTOR protein expression. In contrast, rapamycin treatment reduced pain, improved locomotor activity, and decreased negative mood. It also downregulated PI3K-mTOR protein expression. Furthermore, inhibiting the PI3K-mTOR pathway with a PI3K inhibitor or rapamycin not only improved pain responses and locomotor activity but also reduced depression and anxiety-like behaviors. These effects were accompanied by changes in paw withdrawal threshold, latency, static time, and PI3K-mTOR protein expression.

Conclusions

Targeting the PI3K-mTOR signaling pathway in the ACC effectively alleviates pain-related symptoms and emotional disturbances in rats with bone cancer pain. This approach holds promise for alleviating pain and allaying negative emotion after further study.

Environmental enrichment alleviates neuropathic pain-associated anxiety by enhancing the function of parvalbumin interneurons in the anterior cingulate cortex

Chronic neuropathic pain is often accompanied with comorbid anxiety. However, effective interventions for this anxiety are highly limited. This study aims to examine the effect of environmental enrichment (EE) on spared nerve injury (SNI)-induced neuropathic pain-associated anxiety behaviors and explore the mechanisms underlying this effect. EE effectively ameliorated anxiety-like behaviors followed by SNI. EE also significantly reversed the phenotypic loss of parvalbumin (PV) interneurons in the anterior cingulate cortex (ACC) and impaired gamma oscillations under SNI-induced neuropathic pain conditions. In addition, EE reversed the SNI-induced reduction in the number of PV puncta around Ca²⁺/calmodulin-dependent protein kinase II-positive neurons. Furthermore, enhancing the function of PV interneurons could effectively improve the SNI-caused anxiety-like behaviors. In contrast, the inhibition of PV interneurons led to anxiety-like behaviors in naïve mice. Our findings suggest that EE significantly improves anxiety-like behaviors under neuropathic pain conditions, likely by enhancing the function of PV interneurons in ACC.

Enhanced Analgesic Efficacy and Reduced Side Effects of Morphine by Combination with PD-1 Agonist

Chronic pain is a debilitating disease and remains challenging to treat. Morphine serves as the most commonly used drug for the treatment of pathological pain. However, detrimental side effects (e.g., hyperalgesia and tolerance) manifest during chronic administration, thus counteracting morphine analgesia. Investigators have sought methods to widen the therapeutic window of morphine in the management of chronic pain. Programmed cell death protein 1 (PD-1) is a recently validated analgesic target and is coexpressed with the mu opioid receptor (μOR) in dorsal root ganglion (DRG) sensory neurons. Here, we present evidence that PD-1 regulates the expression of μOR mRNA and influences μOR-mediated analgesia. Notably, the concomitant administration of PD-1 agonist H-20 greatly reduces the dosage of morphine needed for analgesia, thereby significantly decreasing opioid-related side effects. This new combination therapy may provide a solution for managing chronic pain in patients who require morphine.

The elevated open platform stress suppresses excitatory synaptic transmission in the layer V anterior cingulate cortex

There are various forms of stress including; physical, psychological and social stress. Exposure to physical stress can lead to physical sensations (e.g. hyperalgesia) and negative emotions including anxiety and depression in animals and humans. Recently, our studies in mice have shown that acute physical stress induced by the elevated open platform (EOP) can provoke long-lasting mechanical hypersensitivity. This effect appears to be related to activity in the anterior cingulate cortex (ACC) at the synaptic level. Indeed, EOP exposure induces synaptic plasticity in layer II/III pyramidal neurons from the ACC. However, it is still unclear whether or not EOP exposure alters intrinsic properties and synaptic transmission in layer V pyramidal neurons. This is essential because these neurons are known to be a primary output to subcortical structures which may ultimately impact the behavioral stress response. Here, we studied both intrinsic properties and excitatory/inhibitory synaptic transmission by using whole-cell patch-clamp method in brain slice preparations. The EOP exposure did not change intrinsic properties including resting membrane potentials and action potentials. In contrast, EOP exposure suppressed the frequency of miniature and spontaneous excitatory synaptic transmission with an alteration of kinetics of AMPA/GluK receptors. EOP exposure also reduced evoked synaptic transmission induced by electrical stimulation. Furthermore, we investigated projection-selective responses of the mediodorsal thalamus to the layer V ACC neurons. EOP exposure produced short-term depression in excitatory synaptic transmission on thalamo-ACC projections. These results suggest that the EOP stress provokes abnormal excitatory synaptic transmission in layer V pyramidal neurons of the ACC.

Cortical kappa opioid receptors integrate negative affect and sleep disturbance

Sleep disruption and negative affect are attendant features of many psychiatric and neurological conditions that are often co-morbid including major depressive disorder, generalized anxiety disorder and chronic pain. Whether there is a causal relationship between negative affect and sleep disruption remains unclear. We therefore asked if mechanisms promoting negative affect can disrupt sleep and whether inhibition of pathological negative affect can normalize disrupted sleep. Signaling at the kappa opioid receptor (KOR) elicits dysphoria in humans and aversive conditioning in animals. We tested the possibility that (a) increased KOR signaling in the anterior cingulate cortex (ACC), a brain region associated with negative emotions, would be sufficient to promote both aversiveness and sleep disruption and (b) inhibition of KOR signaling would normalize pathological negative affect and sleep disruption induced by chronic pain. Chemogenetic Gi-mediated inhibition of KOR-expressing ACC neurons produced conditioned place aversion (CPA) as well as sleep fragmentation in naïve mice. CRISPR/Cas9 editing of ACC KOR normalized both the negative affect and sleep disruption elicited by pathological chronic pain while maintaining the physiologically critical sensory features of pain. These findings suggest therapeutic utility of KOR antagonists for treatment of disease conditions that are associated with both negative affect and sleep disturbances.

Circadian disruption promotes the neurotoxicity of oligomeric alpha-synuclein in mice

Circadian disruption often arises prior to the onset of typical motor deficits in patients with Parkinson's disease (PD). It remains unclear whether such a prevalent non-motor manifestation would contribute to the progression of PD. Diffusible oligomeric alpha-synuclein (O-αSyn) is perceived as the most toxic and rapid-transmitted species in the early stages of PD. Exploring the factors that influence the spread and toxicity of O-αSyn should be helpful for developing effective interventions for the disease. The aim of this study was to explore the effects of circadian disruption on PD pathology and parkinsonism-like behaviors in a novel mouse model induced by O-αSyn. We discovered that O-αSyn could enter the brain rapidly following intranasal administration, resulting in the formation of nitrated-αSyn pathology and non-motor symptoms of the mice. Meanwhile, circadian disruption exacerbated the burden of nitrated-αSyn pathology and accelerated the loss of dopaminergic neurons in O-αSyn-treated mice. Subsequent experiments demonstrated that circadian disruption might act via promoting nitrative stress and neuroinflammation. These findings could highlight the circadian rhythms as a potential diagnostic and therapeutic target in early-stage PD.

Optogenetic Brain-Computer Interfaces

The brain-computer interface (BCI) is one of the most powerful tools in neuroscience and generally includes a recording system, a processor system, and a stimulation system. Optogenetics has the advantages of bidirectional regulation, high spatiotemporal resolution, and cell-specific regulation, which expands the application scenarios of BCIs. In recent years, optogenetic BCIs have become widely used in the lab with the development of materials and software. The systems were designed to be more integrated, lightweight, biocompatible, and power efficient, as were the wireless transmission and chip-level embedded BCIs. The software is also constantly improving, with better real-time performance and accuracy and lower power consumption. On the other hand, as a cutting-edge technology spanning multidisciplinary fields including molecular biology, neuroscience, material engineering, and information processing, optogenetic BCIs have great application potential in neural decoding, enhancing brain function, and treating neural diseases. Here, we review the development and application of optogenetic BCIs. In the future, combined with other functional imaging techniques such as near-infrared spectroscopy (fNIRS) and functional magnetic resonance imaging (fMRI), optogenetic BCIs can modulate the function of specific circuits, facilitate neurological rehabilitation, assist perception, establish a brain-to-brain interface, and be applied in wider application scenarios.

Astaxanthin alleviates fibromyalgia pain and depression via NLRP3 inflammasome inhibition

Fibromyalgia is characterised by widespread chronic pain and is often accompanied by comorbidities such as sleep disorders, anxiety, and depression. Because it is often accompanied by many adverse symptoms and lack of effective treatment, it is important to search for the pathogenesis and treatment of fibromyalgia. Astaxanthin, a carotenoid pigment known for its anti-inflammatory and antioxidant properties, has demonstrated effective analgesic effects in neuropathic pain. However, its impact on fibromyalgia remains unclear. Therefore, in this study, we constructed a mouse model of fibromyalgia and investigated the effect of astaxanthin on chronic pain and associated symptoms through multiple intragastrical injections. We conducted behavioural assessments to detect pain and depression-like states in mice, recorded electroencephalograms to monitor sleep stages, examined c-Fos activation in the anterior cingulate cortex, measured activation of spinal glial cells, and assessed levels of inflammatory factors in the brain and spinal cord, including interleukin (IL)-1β, IL-6, and tumour necrosis factor- α(TNF-α).Additionally, we analysed the expression levels of IL-6, IL-10, NOD-like receptor thermal protein domain associated protein 3 (NLRP3), Apoptosis-associated speck-like protein containing CARD, and Caspase-1 proteins. The findings revealed that astaxanthin significantly ameliorated mechanical and thermal pain in mice with fibromyalgia and mitigated sleep disorders and depressive-like symptoms induced by pain. A potential mechanism underlying these effects is the anti-inflammatory action of astaxanthin, likely mediated through the inhibition of the NLRP3 inflammasome, which could be one of the pathways through which astaxanthin alleviates fibromyalgia. In conclusion, our study suggests that astaxanthin holds promise as a potential analgesic medication for managing fibromyalgia and its associated symptoms.

Anterior cingulate cortex and insomnia: A cingulate-striatum connection

Insomnia is an important comorbidity of chronic pain. In this issue of Neuron, Li et al. report that chronic-pain-induced insomnia is mediated by the pyramidal neurons in the anterior cingulate cortex and their dopaminergic projections to the dorsal medial striatum.