Targeting thalamic circuits rescues motor and mood deficits in PD mice

Multidimensional mechanisms of anxiety and depression in Parkinson's disease: Integrating neuroimaging, neurocircuits, and molecular pathways

Anxiety and depression are common non-motor symptoms of Parkinson's disease (PD) that significantly affect patients' quality of life. In recent years, our understanding of PD has advanced through multifaceted studies on the pathological mechanisms associated with anxiety and depression in PD. These classic psychiatric symptoms involve complex pathophysiology, with both distinct features and connections to the mechanisms underlying the aetiology of PD. Furthermore, the co-occurrence of anxiety and depression in PD blurs the boundaries between them. Therefore, a comprehensive summary of the pathogenic mechanisms associated with anxiety and depression will aid in better addressing the emergence of these classic psychiatric symptoms in PD. This article integrates neuroanatomical, neural projection, neurotransmitter, neuroinflammatory, brain-gut axis, neurotrophic, hypothalamic-pituitary-adrenal axis, and genetic perspectives to provide a comprehensive description of the core pathological alterations underlying anxiety and depression in PD, aiming to provide an up-to-date perspective and broader therapeutic prospects for PD patients suffering from anxiety or depression.

Deep brain stimulation alleviates Parkinsonian motor deficits through desynchronizing GABA release in mice

High-frequency deep brain stimulation (DBS) at subthalamic nucleus (STN) is an effective therapy for Parkinson's disease (PD), but the underlying mechanisms remain unclear. Here we find an important role of asynchronous release (AR) of GABA induced by high-frequency stimulation (HFS) in alleviating motor functions of dopamine-depleted male mice. Electrophysiological recordings reveal that 130-Hz HFS causes an initial inhibition followed by desynchronization of STN neurons, largely attributable to presynaptic GABA release. Low-frequency stimulation at 20 Hz, however, produces much weaker AR and negligible effects on neuronal firing. Further optogenetic and cell-ablation experiments demonstrate that activation of parvalbumin axons, but not non-parvalbumin axons, from external globus pallidus (GPe) is both necessary and sufficient for DBS effects. Reducing AR diminishes the high-frequency DBS effect, while increasing AR allows low-frequency DBS to achieve a therapeutic benefit. Therefore, asynchronous GABA release from GPe PV neurons may contribute significantly to the therapeutic effects of high-frequency DBS.

Subtle behavioral alterations in the spontaneous behaviors of MPTP mouse model of Parkinson's disease

Midbrain dopamine (DA) neurons are essential for regulating movement, emotion, and reward, with their dysfunction closely linked to Parkinson's disease (PD). While DA neurons in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) have known overlapping roles in behaviors such as depression and reward, their distinct contributions to subtle spontaneous behaviors remain insufficiently understood. In this study, we utilized a 3D behavioral analysis platform powered by machine learning to explore motor and nuanced behavioral changes in a subacute MPTP mouse model of PD. This investigative approach was combined with cell-type-specific genetic ablation of DA neurons in both the SNc and VTA. Our findings highlight significant deficits in rearing, walking, and hunching behaviors correlated with the loss of SNc DA neurons, but not VTA DA neurons, alongside increased overall movement, reduced movement precision, and pronounced right-sided lateralization. These subtle features, particularly rearing deficits and lateralization, emerge as critical behavioral biomarkers of SNc DA neuron loss, thereby enhancing the translational relevance of PD models.

Dissociable roles of distinct thalamic circuits in learning reaches to spatial targets

Reaching movements are critical for survival, and are learned and controlled by distributed motor networks. Even though the thalamus is a highly interconnected node in these networks, its role in learning and controlling reaches remains underexplored. We report dissociable roles of two thalamic forelimb circuits coursing through parafascicular (Pf) and ventroanterior/ventrolateral (VAL) nuclei in refining reaches to a spatial target. Using 2-photon calcium imaging as mice learn directional reaches, we observe high reach-related activity from both circuits early in learning, which decreases with learning. Pf activity encodes reach direction early in learning, more so than VAL. Consistently, bilateral lesions of Pf before training impairs refinement of reach direction. Pre-training lesions of VAL does not affect reach direction, but increases reach speed and target overshoot. Lesions of either nucleus after training does not affect the execution of learned reaches. These findings reveal different thalamic circuits governing distinct aspects of learned reaches.

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.

Gray matter structural and functional brain abnormalities in Parkinson's disease: a meta-analysis of VBM and ALFF data

BACKGROUND

Previous studies based on resting-state functional imaging and voxel-based morphometry (VBM) have revealed structural and functional alterations in several brain regions in patients with Parkinson's disease (PD), but their results have been inconsistent. Furthermore, no studies have investigated specific and common functional and structural alterations in PD.

METHODS

The whole-brain voxel-wise meta-analyses on the VBM and amplitude of low-frequency fluctuation (ALFF) studies were conducted using the Seed-based d Mapping with Permutation of Subject Images (SDM-PSI) software, respectively, with multimodal overlapping to comprehensively identify the gray matter volume (GMV) and spontaneous functional activity changes in patients with PD.

RESULTS

A total of 30 independent studies for ALFF (1413 PD and 1424 HCs) and 27 independent studies for VBM (1236 PD and 1185 HCs) were included. Compared with HCs, patients with PD displayed significantly decreased spontaneous functional activity in the left striatum. For the VBM meta-analysis, patients with PD showed significantly decreased GMV in the right temporal pole: superior temporal gyrus (extending to the right hippocampus, parahippocampal gyrus, and amygdala), the left superior temporal gyrus (extending to the left insula, and temporal pole: superior temporal gyrus), and the left striatum. Furthermore, after overlapping functional and structural differences, patients with PD displayed a conjoint decrease of spontaneous functional activity and GMV in the left striatum.

CONCLUSION

The multimodal meta-analysis revealed that PD showed similar pattern of aberrant brain functional activity and structure in the striatum. In addition, some brain regions within the within the temporal lobe and limbic system displayed only structural deficits. These findings provide useful insights for understanding the underlying pathophysiology of PD.

Distinguish risk genes functioning at presynaptic or postsynaptic regions and key connectomes associated with pathological α-synuclein spreading

Previous studies have suggested that pathological α-synuclein (α-Syn) mainly transmits along the neuronal network, but several key questions remain unanswered: (1) How many and which connections in the connectome are necessary for predicting the progression of pathological α-Syn? (2) How to identify risk gene that affects pathology spreading functioning at presynaptic or postsynaptic regions, and are these genes enriched in different cell types? Here, we addressed these key questions with novel mathematical models. Strikingly, the spreading of pathological α-Syn is predominantly determined by the key subnetworks composed of only 2% of the strongest connections in the connectome. We further explored the genes that are responsible for the selective vulnerability of different brain regions to transmission to distinguish the genes that play roles in presynaptic from those in postsynaptic regions. Those risk genes were significantly enriched in microglial cells of presynaptic regions and neurons of postsynaptic regions. Gene regulatory network analyses were then conducted to identify 'key drivers' of genes responsible for selective vulnerability and overlapping with Parkinson's disease risk genes. By identifying and discriminating between key gene mediators of transmission operating at presynaptic and postsynaptic regions, our study has demonstrated for the first time that these are functionally distinct processes.

Oligodendrocytes drive neuroinflammation and neurodegeneration in Parkinson's disease via the prosaposin-GPR37-IL-6 axis

Parkinson's disease (PD) is a common neurodegenerative disease and is difficult to treat due to its elusive mechanisms. Recent studies have identified a striking association between oligodendrocytes and PD progression, yet how oligodendrocytes regulate the pathogenesis of PD is still unknown. Here, we show that G-protein-coupled receptor 37 (GPR37) is upregulated in oligodendrocytes of the substantia nigra and that prosaposin (PSAP) secretion is increased in parkinsonian mice. The released PSAP can induce interleukin (IL)-6 upregulation and secretion from oligodendrocytes via a GPR37-dependent pathway, resulting in enhanced neuroinflammation, dopamine neuron degeneration, and behavioral deficits. GPR37 deficiency in oligodendrocytes prevents neurodegeneration in multiple PD models. Finally, the hallmarks of the PSAP-GPR37-IL-6 axis are observed in patients with PD. Thus, our results reveal that dopaminergic neurons interact with oligodendrocytes via secreted PSAP, and our findings identify the PSAP-GPR37-IL-6 axis as a driver of PD pathogenesis and a potential therapeutic target that might alleviate PD progression in patients.

Amylopectin-based Hydrogel Probes for Brain-machine Interfaces

Implantable neural probes hold promise for acquiring brain data, modulating neural circuits, and treating various brain disorders. However, traditional implantable probes face significant challenges in practical applications, such as balancing sensitivity with biocompatibility and the difficulties of in situ neural information monitoring and neuromodulation. To address these challenges, this study developed an implantable hydrogel probe capable of recording neural signals, modulating neural circuits, and treating stroke. Amylopectin is integrated into the hydrogels, which can induce reorientation of the poly(3,4-ethylenedioxythiophene) (PEDOT) chain and create compliant interfaces with brain tissues, enhancing both sensitivity and biocompatibility. The hydrogel probe shows the capability of continuously recording deep brain signals for 8 weeks. The hydrogel probe is effectively utilized to study deep brain signals associated with various physiological activities. Neuromodulation and neural signal monitoring are performed directly in the primary motor cortex of rats, enabling control over their limb behaviors through evoked signals. When applied to the primary motor cortex of stroke-affected rats, neuromodulation significantly reduced the brain infarct area, promoted synaptic reorganization, and restored motor functions and balance. This research represents a significant scientific breakthrough in the design of neural probes for brain monitoring, neural circuit modulation, and the development of brain disease therapies.

Thalamic functional connectivity on 7-Tesla magnetic resonance imaging and its relation to motor signs in early-stage Parkinson's disease

Background

It is well known that dysfunction of thalamocortical circuity generates the motor signs that lead to distinct disease processes and prognoses in Parkinson's disease (PD). This study aimed to leverage ultrahigh-field magnetic resonance imaging (MRI) to identify the connectivity alterations of thalamocortical circuity and clarify their relation to motor signs in early PD.

Methods

Patients with early-stage PD (n=55) and healthy controls (HCs, n=56) were recruited from March 2022 to July 2023. All participants underwent 7-Tesla MRI scans as the baseline. Sign scores were calculated from the Movement Disorder Society Unified Parkinson's Disease Rating Scale III. Significant differences in the functional connectivity between the thalamus subregions and cortex between the PD and HC groups were discovered. The association between altered thalamic functional connectivity and sign scores was evaluated using Spearman or Pearson correlation analysis with false discovery rate (FDR) correction.

Results

Compared to the HCs, the patients with early-stage PD exhibited a decreased functional connectivity between thalamic subregions (primary motor, sensory, occipital, premotor, and parietal thalamus regions) and the cortex [voxel-level P<0.001, cluster-level Pfamily-wise error (FWE) <0.05]. Further exploration of the connection pattern within thalamic subregions showed that the connection strength between the primary motor and sensory (t=2.055; P=0.042), sensory and occipital (t=2.173; P=0.032), and occipital and parietal (t=2.365; P=0.020) regions were reduced. Importantly, motor signs in early-stage PD were associated with the alterations of functional connectivity pattern between the parietal thalamus and left dorsolateral part of the superior frontal gyrus (r=-0.272; PFDR =0.049) and the right thalamus (r=-0.267; PFDR =0.048) .

Conclusions

These findings support the use of ultrahigh-field MRI for examining the thalamic subregions and clarifying their involvement in the neural mechanisms of various motor signs in early-stage PD.

Particulate matter induces depression-like behavior through systemic inflammation and brain-derived neurotrophic factors

Particulate matter (PM) has always received widespread attention, PM2.5 pollution is associated with many adverse effects, including cardiovascular, respiratory and metabolic diseases and mood disorders. However, the underlying mechanisms are not yet clear. In this study, the small animal whole body inhalation exposure system collected real-time PM2.5 in the real environment, which can truly reflect the presence status of PM2.5 in the atmospheric environment. This study investigated the depressive like behavior of mice exposed to PM2.5 for a long time and proved its molecular mechanism through RNA-seq. C57BL/6 male mice were exposed to ambient air together with control mice, who breathed air filtered through high-efficiency air particulate filters. Depression like behavior was observed in mice exposed to PM for 4, 6, and 8 weeks through behavioral experiments, EEG signals, and pathological sections. RNA-seq results indicated that the depressive like behavior of mice exposed to PM2.5 might be related to pro-inflammatory and anti-inflammatory cytokines, as well as the BDNF pathways in the hippocampus and olfactory bulb. This study suggests that PM2.5 may induce depression in mice through the MAPK/CREB/BDNF pathway. ENVIRONMENTAL IMPLICATION: Atmospheric particulate matter has been classified as Class 1 pollutant by the International Agency for Research on Cancer. Current research mainly believed that PM2.5 seriously affected lung health, but there was little research on the effects of PM2.5 on other organs. With the improvement of quality of life, people were paying more attention to mental health, while there is little research on the effects of PM2.5 on brain. This study simulated a real PM2.5 exposure environment and explored the effects of PM2.5 on the brain of mice, provided a solid scientific basis for inducing depression after PM2.5 exposure.

Intracerebroventricular injection of α-synuclein preformed fibrils do not induce motor and olfactory impairment in C57BL/6 mice

INTRODUCTION

Alpha-synuclein (αSyn) is believed to play a central role in the pathogenesis of Parkinson's disease (PD). Cerebrospinal fluid (CSF) total αSyn were significantly lower in PD patients, whereas the aggregates were higher, and this phenomenon was further exacerbated with longer disease duration. However, whether CSF αSyn can be the cause and/or a consequence in PD is not fully elucidated.

METHOD

We administered 2 ng or 200 ng αSyn preformed fibrils (PFFs) by intracerebroventricular injection for consecutive 7 days in C57BL/6 mice. The olfactory function was assessed by the olfactory discrimination test and buried food-seeking test. The locomotor function was assessed by the rotarod test, pole test, open field test and CatWalk gait analysis. Phosphorylated αSyn at serine 129 was detected by the immunohistochemistry staining. Iron levels was determined by Perl's-diaminobenzidine iron staining and synchrotron-based X-ray fluorescence.

RESULTS

The mice did not exhibit any diffuse synucleinopathy in the brain for up to 30 weeks, although αSyn PFFs induced aggregation in SH-SY5Y cells and in the substantia nigra and striatum of mice with stereotactic injection. No impairment of motor behaviors or olfactory functions were observed, although there was a temporary motor enhancement at 1 week. We then demonstrated iron levels were comparable in certain brain regions, suggesting there was no iron deposition/redistribution occurred.

CONCLUSION

The intraventricular injection of αSyn PFFs does not induce synucleinopathy or behavioral symptoms. These findings have implications that CSF αSyn aggregates may not necessarily contribute to the onset or progression in PD.

Anemia, blood cell indices, genetic correlations, and brain structures: A comprehensive analysis of roles in Parkinson's disease risk

INTRODUCTION

Anemia may contribute significantly to the onset of Parkinson's disease (PD). Current research on the association between anemia and PD risk is inconclusive, and the relationships between anemia-related blood cell indices and PD incidence require further clarification. This study aims to investigate the relationships between anemia, blood cell indicators, and PD risk using a thorough prospective cohort study.

METHODS

We used data from the UK Biobank, a prospective cohort study of 502,649 participants, and ultimately, 365,982 participants were included in the analysis. Cox proportional hazards models were utilized to adjust for confounding factors, aiming to thoroughly explore the associations between anemia and blood cell indices with the risk of incident PD. The interaction between anemia and Polygenic Risk Score (PRS) for PD was also examined. Linear regression and mediation analyses assessed potential mechanisms driven by brain structures, including grey matter volume.

RESULTS

During a median follow-up of 14.24 years, 2513 participants were diagnosed with PD. Anemia considerably increased PD risk (hazard ratio [HR] 1.98, 95 % confidence interval [CI]: 1.81-2.18, P < 0.001) after adjustments. Those with high PRS for anemia had an 83 % higher PD incidence compared to low PRS participants. Sensitivity analyses confirmed result robustness. Linear regression showed that anemia correlated with grey matter volumes and most white matter tracts. Furthermore, mediation analyses identified that the volume of grey matter in Thalamus mediates the relationship between anemia and PD risk.

CONCLUSION

In summary, we consider there to be a substantial correlation between anemia and increased PD risk.

Identification of a Hippocampus-to-Zona Incerta Projection involved in Motor Learning

Motor learning (ML), which plays a fundamental role in growth and physical rehabilitation, involves different stages of learning and memory processes through different brain regions. However, the neural mechanisms that underlie ML are not sufficiently understood. Here, a previously unreported neuronal projection from the dorsal hippocampus (dHPC) to the zona incerta (ZI) involved in the regulation of ML behaviors is identified. Using recombinant adeno-associated virus, the projections to the ZI are surprisingly identified as originating from the dorsal dentate gyrus (DG) and CA1 subregions of the dHPC. Furthermore, projection-specific chemogenetic and optogenetic manipulation reveals that the projections from the dorsal CA1 to the ZI play key roles in the acquisition and consolidation of ML behaviors, whereas the projections from the dorsal DG to the ZI mediate the retrieval/retention of ML behaviors. The results reveal new projections from the dorsal DG and dorsal CA1 to the ZI involved in the regulation of ML and provide insight into the stages over which this regulation occurs.

Movement-related increases in subthalamic activity optimize locomotion

The subthalamic nucleus (STN) is traditionally thought to restrict movement. Lesion or prolonged STN inhibition increases movement vigor and propensity, while optogenetic excitation has opposing effects. However, STN neurons often exhibit movement-related increases in firing. To address this paradox, STN activity was recorded and manipulated in head-fixed mice at rest and during self-initiated and self-paced treadmill locomotion. We found that (1) most STN neurons (type 1) exhibit locomotion-dependent increases in activity, with half firing preferentially during the propulsive phase of the contralateral locomotor cycle; (2) a minority of STN neurons exhibit dips in activity or are uncorrelated with movement; (3) brief optogenetic inhibition of the lateral STN (where type 1 neurons are concentrated) slows and prematurely terminates locomotion; and (4) in Q175 Huntington's disease mice, abnormally brief, low-velocity locomotion is associated with type 1 hypoactivity. Together, these data argue that movement-related increases in STN activity contribute to optimal locomotor performance.

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.

Dissociable roles of thalamic nuclei in the refinement of reaches to spatial targets

Reaches are complex movements that are critical for survival, and encompass the control of different aspects such as direction, speed, and endpoint precision. Complex movements have been postulated to be learned and controlled through distributed motor networks, of which the thalamus is a highly connected node. Still, the role of different thalamic circuits in learning and controlling specific aspects of reaches has not been investigated. We report dissociable roles of two distinct thalamic nuclei - the parafascicular (Pf) and ventroanterior/ventrolateral (VAL) nuclei - in the refinement of spatial target reaches in mice. Using 2-photon calcium imaging in a head-fixed joystick task where mice learned to reach to a target in space, we found that glutamatergic neurons in both areas were most active during reaches early in learning. Reach-related activity in both areas decreased late in learning, as movement direction was refined and reaches increased in accuracy. Furthermore, the population dynamics of Pf, but not VAL, covaried in different subspaces in early and late learning, but eventually stabilized in late learning. The neural activity in Pf, but not VAL, encoded the direction of reaches in early but not late learning. Accordingly, bilateral lesions of Pf before, but not after learning, strongly and specifically impaired the refinement of reach direction. VAL lesions did not impact direction refinement, but instead resulted in increased speed and target overshoot. Our findings provide new evidence that the thalamus is a critical motor node in the learning and control of reaching movements, with specific subnuclei controlling distinct aspects of the reach early in learning.

An approach based on a combination of toxicological experiments and in silico predictions to investigate the adverse outcome pathway (AOP) of paraquat neuro-immunotoxicity

Paraquat (PQ) exposure is strongly associated with neurotoxicity. However, research on the neurotoxicity mechanisms of PQ varies in terms of endpoints of toxic assessment, resulting in a great challenge to understand the early neurotoxic effects of PQ. In this study, we developed an adverse outcome pathway (AOP) to investigate PQ-induced neuro-immunotoxicity from an immunological perspective, combining of traditional toxicology methods and computer simulations. In vivo, PQ can microstructurally lead to an early synaptic loss in the brain mice, which is a large degree regarded as a main reason for cognitive impairment to mice behavior. Both in vitro and in vivo demonstrated synapse loss is caused by excessive activation of the complement C1q/C3-CD11b pathway, which mediates microglial phagocytosis dysfunction. Additionally, the interaction between PQ and C1q was validated by molecular simulation docking. Our findings extend the AOP framework related to PQ neurotoxicity from a neuro-immunotoxic perspective, highlighting C1q activation as the initiating event for PQ-induced neuro-immunotoxicity. In addition, downstream complement cascades induce abnormal microglial phagocytosis, resulting in reduced synaptic density and subsequent non-motor dysfunction. These findings deepen our understanding of neurotoxicity and provide a theoretical basis for ecological risk assessment of PQ.

Protopanaxadiols Eliminate Behavioral Impairments and Mitochondrial Dysfunction in Parkinson's Disease Mice Model

Currently, there are no effective therapies to cure Parkinson's disease (PD), which is the second most common neurodegenerative disease primarily characterized by motor dysfunction and degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc). Protopanaxadiols (PPDs), including 20 (R)- protopanaxadiol (R-PPD) and 20 (S)- protopanaxadiol (S-PPD), are main metabolites of ginsenosides. The role of ginsenosides in neurodegenerative diseases has been thoroughly studied, however, it is unknown whether PPDs can attenuate behavioral deficits and dopaminergic neuron injury in PD model mice to date. Here, we administered PPDs to MPTP-induced PD model mice and monitored the effects on behavior and dopaminergic neurons to investigate the effects of R-PPD and S-PPD against PD. Our results showed that R-PPD and S-PPD (at a dose of 20 mg/kg, i.g.) treatment alleviated MPTP (30 mg/kg, i.p.) induced behavioral deficits. Besides, R-PPD and S-PPD protected MPP+-induced neuron injury and mitochondrial dysfunction, and reduced the abnormal expression of Cyt C, Bax, caspase-3 and Bcl-2. These findings demonstrate that R-PPD and S-PPD were potentially useful to ameliorate PD.

α-Synuclein pathology from the body to the brain: so many seeds so close to the central soil

ABSTRACT

α-Synuclein is a protein that mainly exists in the presynaptic terminals. Abnormal folding and accumulation of α-synuclein are found in several neurodegenerative diseases, including Parkinson's disease. Aggregated and highly phosphorylated α-synuclein constitutes the main component of Lewy bodies in the brain, the pathological hallmark of Parkinson's disease. For decades, much attention has been focused on the accumulation of α-synuclein in the brain parenchyma rather than considering Parkinson's disease as a systemic disease. Recent evidence demonstrates that, at least in some patients, the initial α-synuclein pathology originates in the peripheral organs and spreads to the brain. Injection of α-synuclein preformed fibrils into the gastrointestinal tract triggers the gut-to-brain propagation of α-synuclein pathology. However, whether α-synuclein pathology can occur spontaneously in peripheral organs independent of exogenous α-synuclein preformed fibrils or pathological α-synuclein leakage from the central nervous system remains under investigation. In this review, we aimed to summarize the role of peripheral α-synuclein pathology in the pathogenesis of Parkinson's disease. We also discuss the pathways by which α-synuclein pathology spreads from the body to the brain.

Low and high-order topological disruption of functional networks in multiple system atrophy with freezing of gait: A resting-state study

OBJECTIVE

Freezing of gait (FOG), a specific survival-threatening gait impairment, needs to be urgently explored in patients with multiple system atrophy (MSA), which is characterized by rapid progression and death within 10 years of symptom onset. The objective of this study was to explore the topological organisation of both low- and high-order functional networks in patients with MAS and FOG.

METHOD

Low-order functional connectivity (LOFC) and high-order functional connectivity FC (HOFC) networks were calculated and further analysed using the graph theory approach in 24 patients with MSA without FOG, 20 patients with FOG, and 25 healthy controls. The relationship between brain activity and the severity of freezing symptoms was investigated in patients with FOG.

RESULTS

Regarding global topological properties, patients with FOG exhibited alterations in the whole-brain network, dorsal attention network (DAN), frontoparietal network (FPN), and default network (DMN), compared with patients without FOG. At the node level, patients with FOG showed decreased nodal centralities in sensorimotor network (SMN), DAN, ventral attention network (VAN), FPN, limbic regions, hippocampal network and basal ganglia network (BG), and increased nodal centralities in the FPN, DMN, visual network (VIN) and, cerebellar network. The nodal centralities of the right inferior frontal sulcus, left lateral amygdala and left nucleus accumbens (NAC) were negatively correlated with the FOG severity.

CONCLUSION

This study identified a disrupted topology of functional interactions at both low and high levels with extensive alterations in topological properties in MSA patients with FOG, especially those associated with damage to the FPN. These findings offer new insights into the dysfunctional mechanisms of complex networks and suggest potential neuroimaging biomarkers for FOG in patients with MSA.

Multiple cholinergic receptor subtypes coordinate dual modulation of acetylcholine on anterior and posterior paraventricular thalamic neurons

Paraventricular thalamus (PVT) plays important roles in the regulation of emotion and motivation through connecting many brain structures including the midbrain and the limbic system. Although acetylcholine (ACh) neurons of the midbrain were reported to send projections to PVT, little is known about how cholinergic signaling regulates PVT neurons. Here, we used both RNAscope and slice patch-clamp recordings to characterize cholinergic receptor expression and ACh modulation of PVT neurons in mice. We found ACh excited a majority of anterior PVT (aPVT) neurons but predominantly inhibited posterior PVT (pPVT) neurons. Compared to pPVT with more inhibitory M2 receptors, aPVT expressed higher levels of all excitatory receptor subtypes including nicotinic α4, α7, and muscarinic M1 and M3. The ACh-induced excitation was mimicked by nicotine and antagonized by selective blockers for α4β2 and α7 nicotinic ACh receptor (nAChR) subtypes as well as selective antagonists for M1 and M3 muscarinic ACh receptors (mAChR). The ACh-induced inhibition was attenuated by selective M2 and M4 mAChR receptor antagonists. Furthermore, we found ACh increased the frequency of excitatory postsynaptic currents (EPSCs) on a majority of aPVT neurons but decreased EPSC frequency on a larger number of pPVT neurons. In addition, ACh caused an acute increase followed by a lasting reduction in inhibitory postsynaptic currents (IPSCs) on PVT neurons of both subregions. Together, these data suggest that multiple AChR subtypes coordinate a differential modulation of ACh on aPVT and pPVT neurons.

Movement-related increases in subthalamic activity optimize locomotion

The subthalamic nucleus (STN) is traditionally thought to restrict movement. Lesion or prolonged STN inhibition increases movement vigor and propensity, while ontogenetic excitation typically has opposing effects. Subthalamic and motor activity are also inversely correlated in movement disorders. However, most STN neurons exhibit movement-related increases in firing. To address this paradox, STN activity was recorded and manipulated in head-fixed mice at rest and during self-initiated treadmill locomotion. The majority of STN neurons (type 1) exhibited locomotion-dependent increases in activity, with half encoding the locomotor cycle. A minority of neurons exhibited dips in activity or were uncorrelated with movement. Brief optogenetic inhibition of the dorsolateral STN (where type 1 neurons are concentrated) slowed and prematurely terminated locomotion. In Q175 Huntington's disease mice abnormally brief, low-velocity locomotion was specifically associated with type 1 hyperactivity. Together these data argue that movement-related increases in STN activity contribute to optimal locomotor performance.

Repurposing Ketamine in the Therapy of Depression and Depression-Related Disorders: Recent Advances and Future Potential

Depression represents a prevalent and enduring mental disorder of significant concern within the clinical domain. Extensive research indicates that depression is very complex, with many interconnected pathways involved. Most research related to depression focuses on monoamines, neurotrophic factors, the hypothalamic-pituitary-adrenal axis, tryptophan metabolism, energy metabolism, mitochondrial function, the gut-brain axis, glial cell-mediated inflammation, myelination, homeostasis, and brain neural networks. However, recently, Ketamine, an ionotropic N-methyl-D-aspartate (NMDA) receptor antagonist, has been discovered to have rapid antidepressant effects in patients, leading to novel and successful treatment approaches for mood disorders. This review aims to summarize the latest findings and insights into various signaling pathways and systems observed in depression patients and animal models, providing a more comprehensive view of the neurobiology of anxious-depressive-like behavior. Specifically, it highlights the key mechanisms of ketamine as a rapid-acting antidepressant, aiming to enhance the treatment of neuropsychiatric disorders. Moreover, we discuss the potential of ketamine as a prophylactic or therapeutic intervention for stress-related psychiatric disorders.

Restoring the Function of Thalamocortical Circuit Through Correcting Thalamic Kv3.2 Channelopathy Normalizes Fear Extinction Impairments in a PTSD Mouse Model

Impaired extinction of fear memory is one of the most common symptoms in post-traumatic stress disorder (PTSD), with limited therapeutic strategies due to the poor understanding of its underlying neural substrates. In this study, functional screening is performed and identified hyperactivity in the mediodorsal thalamic nucleus (MD) during fear extinction. Furthermore, the encoding patterns of the hyperactivated MD is investigated during persistent fear responses using multiple machine learning algorithms. The anterior cingulate cortex (ACC) is also identified as a functional downstream region of the MD that mediates the extinction of fear memory. The thalamocortical circuit is comprehensively analyzed and found that the MD-ACC parvalbumin interneurons circuit is preferentially enhanced in PTSD mice, disrupting the local excitatory and inhibitory balance. It is found that decreased phosphorylation of the Kv3.2 channel contributed to the hyperactivated MD, primarily to the malfunctioning thalamocortical circuit. Using a lipid nanoparticle-based RNA therapy strategy, channelopathy is corrected via a methoxylated siRNA targeting the protein phosphatase 6 catalytic subunit and restored fear memory extinction in PTSD mice. These findings highlight the function of the thalamocortical circuit in PTSD-related impaired extinction of fear memory and provide therapeutic insights into Kv3.2-targeted RNA therapy for PTSD.

Characterization of graded 6-Hydroxydopamine unilateral lesion in medial forebrain bundle of mice

Parkinson's disease (PD) is the second most common age-related neurodegenerative disease, with a progressive loss of dopaminergic cells and fibers. The purpose of this study was to use different doses of 6-hydroxydopamine (6-OHDA) injection into the medial forebrain bundle (MFB) of mice to mimic the different stages of the disease and to characterize in detail their motor and non-motor behavior, as well as neuropathological features in the nigrostriatal pathway. MFB were injected with 0.5 μg, 1 μg, 2 μg of 6-OHDA using a brain stereotaxic technique. 6-OHDA induced mitochondrial damage dose-dependently, as well as substantia nigra pars compacta (SNpc) tyrosine hydroxylase-positive (TH+) cell loss and striatal TH fiber loss. Activation of astrocytes and microglia in the SNpc and striatum were consistently observed at 7 weeks, suggesting a long-term glial response in the nigrostriatal system. Even with a partial or complete denervation of the nigrostriatal pathway, 6-OHDA did not cause anxiety, although depression-like behavior appeared. Certain gait disturbances were observed in 0.5 μg 6-OHDA lesioned mice, and more extensive in 1 μg group. Despite the loss of more neurons from 2 μg 6-OHDA, there was no further impairment in behaviors compared to 1 μg 6-OHDA. Our data have implications that 1 μg 6-OHDA was necessary and sufficient to induce motor and non-motor symptoms in mice, thus a valuable mouse tool to explore disease progression and new treatment in PD.

Long-term labeling and imaging of synaptically connected neuronal networks in vivo using double-deletion-mutant rabies viruses

Rabies-virus-based monosynaptic tracing is a widely used technique for mapping neural circuitry, but its cytotoxicity has confined it primarily to anatomical applications. Here we present a second-generation system for labeling direct inputs to targeted neuronal populations with minimal toxicity, using double-deletion-mutant rabies viruses. Viral spread requires expression of both deleted viral genes in trans in postsynaptic source cells. Suppressing this expression with doxycycline following an initial period of viral replication reduces toxicity to postsynaptic cells. Longitudinal two-photon imaging in vivo indicated that over 90% of both presynaptic and source cells survived for the full 12-week course of imaging. Ex vivo whole-cell recordings at 5 weeks postinfection showed that the second-generation system perturbs input and source cells much less than the first-generation system. Finally, two-photon calcium imaging of labeled networks of visual cortex neurons showed that their visual response properties appeared normal for 10 weeks, the longest we followed them.

Levodopa improved different motor symptoms in patients with Parkinson's disease by reducing the functional connectivity of specific thalamic subregions

BACKGROUND

The thalamus is an important relay station for the motor circuit of human. Levodopa can reverse the clinical manifestations by modulating the function of motor circuits, but its detailed mechanisms are still not fully understood. We aimed to explore (1) the mechanism by which levodopa modulates the functional connectivity (FC) in the subregions of the thalamus; (2) the relationship between the changed FC and the improvement of motor symptoms in Parkinson's disease (PD) patients.

METHODS

Resting-state functional MRI was used to scan 36 PD patients and 37 healthy controls. The FC between the subregions in the thalamus and the whole brain was measured and compared under different medication states of PD patients. The correlation between the improvement of motor symptoms and changes in FC in the thalamus subregions was examined.

RESULTS

The PD on state exhibited decreased FC between the right pre-motor thalamus and the right postcentral gyrus, as well as the right lateral pre-frontal thalamus and the right postcentral gyrus. These decreases were positively correlated with the improvement of resting tremor. The PD on state also exhibited decreased FC between the left lateral pre-frontal thalamus and right paracentral lobule, which was positively correlated with the improvement of bradykinesia.

CONCLUSIONS

This study demonstrates that levodopa treats PD by decreasing the FC between the thalamus subregions and pre/post-central cortex. Our results provide a basis for further exploration of the functional activity of thalamic subregions and offer new insights into the precision treatment in PD patients.

Protocol for MRI-guided virus injection in macaque deep brain regions

Effective delivery of viruses into required brain regions is critical to the success of optogenetic or chemogenetic experiments. However, in monkeys, due to the large size and heterogeneity of their brain, precise injections in deep brain regions have been challenging. Here, we present a protocol for virus injection in monkey deep brain regions under the guidance of MRI. We describe the steps for installing the guiding grid, MRI scanning, MRI-based localization, and virus injection. For complete details on the use and execution of this protocol, please refer to Chen et al. (2023).1.

Updates on brain regions and neuronal circuits of movement disorders in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease with a global burden that affects more often in the elderly. The basal ganglia (BG) is believed to account for movement disorders in PD. More recently, new findings in the original regions in BG involved in motor control, as well as the new circuits or new nucleuses previously not specifically considered were explored. In the present review, we provide up-to-date information related to movement disorders and modulations in PD, especially from the perspectives of brain regions and neuronal circuits. Meanwhile, there are updates in deep brain stimulation (DBS) and other factors for the motor improvement in PD. Comprehensive understandings of brain regions and neuronal circuits involved in motor control could benefit the development of novel therapeutical strategies in PD.

Distributed dopaminergic signaling in the basal ganglia and its relationship to motor disability in Parkinson's disease

The degeneration of mesencephalic dopaminergic neurons that innervate the basal ganglia is responsible for the cardinal motor symptoms of Parkinson's disease (PD). It has been thought that loss of dopaminergic signaling in one basal ganglia region - the striatum - was solely responsible for the network pathophysiology causing PD motor symptoms. While our understanding of dopamine (DA)'s role in modulating striatal circuitry has deepened in recent years, it also has become clear that it acts in other regions of the basal ganglia to influence movement. Underscoring this point, examination of a new progressive mouse model of PD shows that striatal dopamine DA depletion alone is not sufficient to induce parkinsonism and that restoration of extra-striatal DA signaling attenuates parkinsonian motor deficits once they appear. This review summarizes recent advances in the effort to understand basal ganglia circuitry, its modulation by DA, and how its dysfunction drives PD motor symptoms.

Neuronal and synaptic adaptations underlying the benefits of deep brain stimulation for Parkinson's disease

Deep brain stimulation (DBS) is a well-established and effective treatment for patients with advanced Parkinson's disease (PD), yet its underlying mechanisms remain enigmatic. Optogenetics, primarily conducted in animal models, provides a unique approach that allows cell type- and projection-specific modulation that mirrors the frequency-dependent stimulus effects of DBS. Opto-DBS research in animal models plays a pivotal role in unraveling the neuronal and synaptic adaptations that contribute to the efficacy of DBS in PD treatment. DBS-induced neuronal responses rely on a complex interplay between the distributions of presynaptic inputs, frequency-dependent synaptic depression, and the intrinsic excitability of postsynaptic neurons. This orchestration leads to conversion of firing patterns, enabling both antidromic and orthodromic modulation of neural circuits. Understanding these mechanisms is vital for decoding position- and programming-dependent effects of DBS. Furthermore, patterned stimulation is emerging as a promising strategy yielding long-lasting therapeutic benefits. Research on the neuronal and synaptic adaptations to DBS may pave the way for the development of more enduring and precise modulation patterns. Advanced technologies, such as adaptive DBS or directional electrodes, can also be integrated for circuit-specific neuromodulation. These insights hold the potential to greatly improve the effectiveness of DBS and advance PD treatment to new levels.

Dysconnectivity of the parafascicular nucleus in Parkinson's disease: A dynamic causal modeling analysis

BACKGROUND

Recent animal model studies have suggested that the parafascicular nucleus has the potential to be an effective deep brain stimulation target for Parkinson's disease. However, our knowledge on the role of the parafascicular nucleus in Parkinson's disease patients remains limited.

OBJECTIVE

We aimed to investigate the functional alterations of the parafascicular nucleus projections in Parkinson's disease patients.

METHODS

We enrolled 72 Parkinson's disease patients and 60 healthy controls, then utilized resting-state functional MRI and spectral dynamic causal modeling to explore the effective connectivity of the bilateral parafascicular nucleus to the dorsal putamen, nucleus accumbens, and subthalamic nucleus. The associations between the effective connectivity of the parafascicular nucleus projections and clinical features were measured with Pearson partial correlations.

RESULTS

Compared with controls, the effective connectivity from the parafascicular nucleus to dorsal putamen was significantly increased, while the connectivity to the nucleus accumbens and subthalamic nucleus was significantly reduced in Parkinson's disease patients. There was a significantly positive correlation between the connectivity of parafascicular nucleus-dorsal putamen projection and motor deficits. The connectivity from the parafascicular nucleus to the subthalamic nucleus was negatively correlated with motor deficits and apathy, while the connectivity from the parafascicular nucleus to the nucleus accumbens was negatively associated with depression.

CONCLUSION

The present study demonstrates that the parafascicular nucleus-related projections are damaged and associated with clinical symptoms of Parkinson's disease. Our findings provide new insights into the impaired basal ganglia-thalamocortical circuits and give support for the parafascicular nucleus as a potential effective neuromodulating target of the disease.

Pharmacological and Behavioral Interventions for Fatigue in Parkinson's Disease: A Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

This study aims to evaluate pharmacological and behavioral interventions for the treatment of fatigue in Parkinson's disease (PD) patients.

METHODS

We systematically searched PubMed, PsycINFO, Web of Science, EMBASE, CNKI, Wan fang, and VIP up to July 31, 2022. We used Revman 5.3 software for the meta-analysis. The outcomes included Fatigue Severity Scale (FSS) and Parkinson's Fatigue Scale (PFS). The mean difference (MD) and 95% confidence intervals (CI) were collected or calculated.

RESULTS

Thirteen randomized controlled trials (RCTs) with a total of 1758 patients were included. The meta-analysis showed that current clinical treatments reduced FSS (MD: -1.60, 95% CI: -3.14 to -0.05) and PFS (MD: -0.61, 95% CI: -1.17 to -0.05) in patients with PD. Subgroup meta-analysis showed that: (1) neither pharmacological interventions nor behavioral interventions reduced FSS in PD patients; (2) dopaminergic drugs dose-dependently significantly reduced the PFS in patients with PD; (3) behavioral interventions have an almost significant effect (MD: -6.69, 95% CI: -13.71 to 0.33, P = 0.06, I2 = 74%) on alleviating PFS in PD patients; (4) vestibular rehabilitation training significantly reduced the PFS in patients with PD.

CONCLUSIONS

Current clinical treatments alleviate fatigue in PD patients. Dopaminergic drugs may act a stronger effect than amphetamines. Behavioral interventions, especially vestibular rehabilitation training, may be a promising way for the treatment of fatigue in patients with PD though further evidence is still needed.

Spatial Distribution of Parvalbumin-Positive Fibers in the Mouse Brain and Their Alterations in Mouse Models of Temporal Lobe Epilepsy and Parkinson's Disease

Parvalbumin interneurons belong to the major types of GABAergic interneurons. Although the distribution and pathological alterations of parvalbumin interneuron somata have been widely studied, the distribution and vulnerability of the neurites and fibers extending from parvalbumin interneurons have not been detailly interrogated. Through the Cre recombinase-reporter system, we visualized parvalbumin-positive fibers and thoroughly investigated their spatial distribution in the mouse brain. We found that parvalbumin fibers are widely distributed in the brain with specific morphological characteristics in different regions, among which the cortex and thalamus exhibited the most intense parvalbumin signals. In regions such as the striatum and optic tract, even long-range thick parvalbumin projections were detected. Furthermore, in mouse models of temporal lobe epilepsy and Parkinson's disease, parvalbumin fibers suffered both massive and subtle morphological alterations. Our study provides an overview of parvalbumin fibers in the brain and emphasizes the potential pathological implications of parvalbumin fiber alterations.

Chemogenetic and optogenetic stimulation of zona incerta GABAergic neurons ameliorates motor impairment in Parkinson's disease

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons in the substantia nigra and leads to progressive motor dysfunction. While studies have focused on the basal ganglia network, recent evidence suggests neuronal systems outside the basal ganglia are also related to PD pathogenesis. The zona incerta (ZI) is a predominantly inhibitory subthalamic region for global behavioral modulation. This study investigates the role of GABAergic neurons in the ZI in a mouse model of 6-hydroxydopamine (6-OHDA)-induced PD. First, we found a decrease in GABA-positive neurons in the ZI, and then the mice used chemogenetic/optogenetic stimulation to activate or inhibit GABAergic neurons. The motor performance of PD mice was significantly improved by chemogenetic/optogenetic activation of GABAergic neurons, and repeated chemogenetic activation of ZI GABAergic neurons increased the dopamine content in the striatum. Our work identifies the role of ZI GABAergic neurons in regulating motor behaviors in 6-OHDA-lesioned PD model mice.

Cognitive effects of thalamostriatal degeneration are ameliorated by normalizing striatal cholinergic activity

The loss of neurons in parafascicular thalamus (Pf) and their inputs to dorsomedial striatum (DMS) in Lewy body disease (LBD) and Parkinson's disease dementia (PDD) have been linked to the effects of neuroinflammation. We found that, in rats, these inputs were necessary for both the function of striatal cholinergic interneurons (CINs) and the flexible encoding of the action-outcome (AO) associations necessary for goal-directed action, producing a burst-pause pattern of CIN firing but only during the remapping elicited by a shift in AO contingency. Neuroinflammation in the Pf abolished these changes in CIN activity and goal-directed control after the shift in contingency. However, both effects were rescued by either the peripheral or the intra-DMS administration of selegiline, a monoamine oxidase B inhibitor that we found also enhances adenosine triphosphatase activity in CINs. These findings suggest a potential treatment for the cognitive deficits associated with neuroinflammation affecting the function of the Pf and related structures.

Integrated analysis of metabolomic and transcriptomic profiling reveals the effect of Buyang Huanwu decoction on Parkinson's disease in mice

BACKGROUND

Parkinson's disease (PD) is a common, complex, and chronic neurodegenerative disorder involved in multi-system. At present, medicine for PD has many limitations. Buyang Huanwu decoction (BHD), a famous traditional Chinese medicinal (TCM) formulae, is used in the treatment of PD clinically in China. However, the therapeutic mechanism is still unknown.

PURPOSE

We aimed to explore the pharmacological mechanism of BHD alleviating PD through an integrated liver metabolome and brain transcriptome analysis.

METHODS

The mice with PD were induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Behavioral tests and immunohistochemistry were used to evaluate the neuroprotective effects of BHD. The non-targeted metabolomics analysis was conducted to profile differentially accumulated metabolites (DAMs) in the liver using a UHPLC-Q-Exactive MS/MS method. The differentially expressed genes (DEGs) in the brain were investigated by transcriptomic analysis on an Illumina sequencing platform. The correlations of DAMs and DEGs were investigated using an integrated metabolomic and transcriptomic approach.

RESULTS

The results of behavioral tests and immunohistochemistry proved the alleviated effects of BHD on PD symptoms. A total of 14 and 36 DAMs were detected in the groups treated with low- (L group) and high-dose (H group) BHD respectively under the positive ion mode. Compared with the PD model group (M group), three enriched pathways including metabolic pathways, ABC transporters, and biosynthesis of amino acids were common in the L and H group. Transcriptomic analysis proved that BHD could regulate the expression of numerous genes, some of which were targeted by Ben-Ldopa such as Creb5, Gm45623, Ccer2, Cd180, Fosl2, Crip3, and Noxred1. Based on the integrated metabolomic and transcriptomic analysis, 7 metabolite-gene pairs were found in four comparisons, including C vs M, M vs P, M vs L, and M vs H, and 6 enriched pathways containing purine metabolism, glycine/serine/threonine metabolism, phenylalanine metabolism, carbon fixation in photosynthetic organisms, thiamine metabolism, and ABC transporters were overlapped.

CONCLUSIONS

Though the underlying pharmacological mechanism of BHD is still lacking, we provided evidence that BHD could improve dopaminergic neurons in MPTP-induced PD mice by regulating liver metabolism and brain transcriptome. The correlation between the liver and the brain was preliminarily revealed in this study.

Monosynaptic restriction of the anterograde herpes simplex virus strain H129 for neural circuit tracing

Identification of synaptic partners is a fundamental task for systems neuroscience. To date, few reliable techniques exist for whole brain labeling of downstream synaptic partners in a cell-type-dependent and monosynaptic manner. Herein, we describe a novel monosynaptic anterograde tracing system based on the deletion of the gene UL6 from the genome of a cre-dependent version of the anterograde Herpes Simplex Virus 1 strain H129. Given that this knockout blocks viral genome packaging and thus viral spread, we reasoned that co-infection of a HSV H129 ΔUL6 virus with a recombinant adeno-associated virus expressing UL6 in a cre-dependent manner would result in monosynaptic spread from target cre-expressing neuronal populations. Application of this system to five nonreciprocal neural circuits resulted in labeling of neurons in expected projection areas. While some caveats may preclude certain applications, this system provides a reliable method to label postsynaptic partners in a brain-wide fashion.

Neural modulation with photothermally active nanomaterials

Modulating neural electrophysiology with high precision is essential for understanding neural communication and for the diagnosis and treatment of neural disorders. Photothermal modulation offers a remote and non-genetic method for neural modulation with high spatiotemporal resolution and specificity. This technique induces highly localized and transient temperature changes at the cell membrane interfaced with photothermally active nanomaterials. This rapid temperature change affects the electrical properties of the cell membrane or temperature-sensitive ion channels. In this Review, we discuss the fundamental material properties and illumination conditions that are necessary for nanomaterial-assisted photothermal neural excitation and inhibition. We examine how this versatile technique allows direct investigation of neural electrophysiology and signalling pathways in two-dimensional and three-dimensional cell cultures and tissues, and highlight the scientific and technological challenges in terms of cellular specificity, light delivery and biointerface stability on the road to clinical translation.

Striatal μ-opioid receptor activation triggers direct-pathway GABAergic plasticity and induces negative affect

Withdrawal from chronic opioid use often causes hypodopaminergic states and negative affect, which may drive relapse. Direct-pathway medium spiny neurons (dMSNs) in the striatal patch compartment contain μ-opioid receptors (MORs). It remains unclear how chronic opioid exposure and withdrawal impact these MOR-expressing dMSNs and their outputs. Here, we report that MOR activation acutely suppressed GABAergic striatopallidal transmission in habenula-projecting globus pallidus neurons. Notably, withdrawal from repeated morphine or fentanyl administration potentiated this GABAergic transmission. Furthermore, intravenous fentanyl self-administration enhanced GABAergic striatonigral transmission and reduced midbrain dopaminergic activity. Fentanyl-activated striatal neurons mediated contextual memory retrieval required for conditioned place preference tests. Importantly, chemogenetic inhibition of striatal MOR+ neurons rescued fentanyl withdrawal-induced physical symptoms and anxiety-like behaviors. These data suggest that chronic opioid use triggers GABAergic striatopallidal and striatonigral plasticity to induce a hypodopaminergic state, which may promote negative emotions and relapse.

Distinct reward processing by subregions of the nucleus accumbens

The nucleus accumbens (NAc) plays an important role in motivation and reward processing. Recent studies suggest that different NAc subnuclei differentially contribute to reward-related behaviors. However, how reward is encoded in individual NAc neurons remains unclear. Using in vivo single-cell resolution calcium imaging, we find diverse patterns of reward encoding in the medial and lateral shell subdivision of the NAc (NAcMed and NAcLat, respectively). Reward consumption increases NAcLat activity but decreases NAcMed activity, albeit with high variability among neurons. The heterogeneity in reward encoding could be attributed to differences in their synaptic inputs and transcriptional profiles. Specific optogenetic activation of Nts-positive neurons in the NAcLat promotes positive reinforcement, while activation of Cartpt-positive neurons in the NAcMed induces behavior aversion. Collectively, our study shows the organizational and transcriptional differences in NAc subregions and provides a framework for future dissection of NAc subregions in physiological and pathological conditions.

Changed firing activity of nigra dopaminergic neurons in Parkinson's disease

Parkinson's disease is the second most common neurodegenerative disease which is characterized by selective degeneration of dopaminergic neurons in the substantia nigra pars compacta. The intrinsic neuronal firing activity is critical for the functional organization of brain and the specific deficits of neuronal firing activity may be associated with different brain disorders. It is known that the surviving nigra dopaminergic neurons exhibit altered firing activity, such as decreased spontaneous firing frequency, reduced number of firing neurons and increased burst firing in Parkinson's disease. Several ionic mechanisms are involved in changed firing activity of dopaminergic neurons under parkinsonian state. In this review, we summarize the changes of spontaneous firing activity as well as the possible mechanisms of nigra dopaminergic neurons in Parkinson's disease. This review may let us clearly understand the involvement of neuronal firing activity of nigra dopaminergic neurons in Parkinson's disease.

Thalamic pathways mediating motor and non-motor symptoms in a Parkinson's disease model

In a recent study, Zhang, Roy, and colleagues have shown that neurons in the parafascicular (PF) thalamus project to three distinct neural structures in the basal ganglia. The neural circuits identified in the study were associated with specific motor and non-motor symptoms in a Parkinson's disease (PD) mouse model. The findings provide potential actionable therapeutic targets for this disease.

Closed-Loop Adaptive Deep Brain Stimulation in Parkinson's Disease: Procedures to Achieve It and Future Perspectives

Parkinson's disease (PD) is a neurodegenerative disease with a heavy burden on patients, families, and society. Deep brain stimulation (DBS) can improve the symptoms of PD patients for whom medication is insufficient. However, current open-loop uninterrupted conventional DBS (cDBS) has inherent limitations, such as adverse effects, rapid battery consumption, and a need for frequent parameter adjustment. To overcome these shortcomings, adaptive DBS (aDBS) was proposed to provide responsive optimized stimulation for PD. This topic has attracted scientific interest, and a growing body of preclinical and clinical evidence has shown its benefits. However, both achievements and challenges have emerged in this novel field. To date, only limited reviews comprehensively analyzed the full framework and procedures for aDBS implementation. Herein, we review current preclinical and clinical data on aDBS for PD to discuss the full procedures for its achievement and to provide future perspectives on this treatment.

Genetically engineered mesenchymal stem cells with dopamine synthesis for Parkinson's disease in animal models

Although striatal delivery of three critical genes for dopamine synthesis by viruses is a potential clinical approach for treating Parkinson's disease (PD), the approach makes it difficult to finely control dopamine secretion amounts and brings safety concerns. Here, we generate genetically engineered mesenchymal stem cells encoding three critical genes for dopamine synthesis (DOPA-MSCs). DOPA-MSCs retain their MSC identity and stable ability to secrete dopamine during passaging. Following transplantation, DOPA-MSCs reinstate striatal dopamine levels and correct motor function in PD rats. Importantly, after grafting into the caudate and putamen, DOPA-MSCs provide homotopic reconstruction of midbrain dopamine pathways by restoring striatal dopamine levels, and safely and long-term (up to 51 months) correct motor disorders and nonmotor deficits in acute and chronic PD rhesus monkey models of PD even with advanced PD symptoms. The long-term benefits and safety results support the idea that the development of dopamine-synthesized engineered cell transplantation is an important strategy for treating PD.

Connectivity of the corticostriatal and thalamostriatal systems in normal and parkinsonian states: An update

The striatum receives abundant glutamatergic afferents from the cortex and thalamus. These inputs play a major role in the functions of the striatal neurons in normal conditions, and are significantly altered in pathological states, such as Parkinson's disease. This review summarizes the current knowledge of the connectivity of the corticostriatal and thalamostriatal pathways, with emphasis on the most recent advances in the field. We also discuss novel findings regarding structural changes in cortico- and thalamostriatal connections that occur in these connections as a consequence of striatal loss of dopamine in parkinsonism.