Glibenclamide promotes FGF21 secretion in interscapular BAT and attenuates depression-like behaviors in male mice with HFD-induced obesity.

AIMS: Epidemiological evidence suggests that comorbidity of obesity and depression is extremely common and continues to grow in prevalence. However, the mechanisms connecting these two conditions are unknown. In this study, we explored how treatment with KATP channel blocker glibenclamide (GB) or the well-known metabolic regulator FGF21 impact male mice with high-fat diet (HFD)-induced obesity and depressive-like behaviors. MATERIALS AND METHODS: Mice were fed with HFD for 12 weeks and then treated with recombinant FGF21 protein by infusion for 2 weeks, followed by intraperitoneal injection of 3 mg/kg recombinant FGF21 once per day for 4 days. Measurements were made of catecholamine levels, energy expenditure, biochemical endpoints and behavior tests, including sucrose preference and forced swim tests were. Alternatively, animals were infused with GB into brown adipose tissue (BAT). The WT-1 brown adipocyte cell line was used for molecular studies. KEY FINDINGS: Compared to HFD controls, HFD + FGF21 mice exhibited less severe metabolic disorder symptoms, improved depressive-like behaviors, and more extensive mesolimbic dopamine projections. FGF21 treatment also rescued HFD-induced dysregulation of FGF21 receptors (FGFR1 and co-receptor ß-klotho) in the ventral tegmental area (VTA), and it altered dopaminergic neuron activity and morphology in HFD-fed mice. Importantly, we also found that FGF21 mRNA level and FGF21 release were increased in BAT after administration of GB, and GB treatment to BAT reversed HFD-induced dysregulation of FGF21 receptors in the VTA. SIGNIFICANCE: GB administration to BAT stimulates FGF21 production in BAT, corrects HFD-induced dysregulation of FGF21 receptor dimers in VTA dopaminergic neurons, and attenuates depression-like symptoms.

Neural Plasticity in the Ventral Tegmental Area, Aversive Motivation during Drug Withdrawal and Hallucinogenic Therapy.

Aberrant glutamatergic signaling has been closely related to several pathologies of the central nervous system. Glutamatergic activity can induce an increase in neural plasticity mediated by brain-derived neurotrophic factor (BDNF) in the ventral tegmental area (VTA), a nodal point in the mesolimbic dopamine system. Recent studies have related BDNF dependent plasticity in the VTA with the modulation of aversive motivation to deal with noxious environmental stimuli. The disarray of these learning mechanisms would produce an abnormal augmentation in the representation of the emotional information related to aversion, sometimes even in the absence of external environmental trigger, inducing pathologies linked to mood disorders such as depression and drug addiction. Recent studies point out that serotonin (5-hydroxytryptamine, 5-HT) receptors, especially the 2a (5-HT2a) subtype, play an important role in BDNF-related neural plasticity in the VTA. It has been observed that a single administration of a 5HT2a agonist can both revert an animal to a nondependent state from a drug-dependent state (produced by the chronic administration of a substance of abuse). The 5HT2a agonist also reverted the BDNF-induced neural plasticity in the VTA, suggesting that the administration of 5-HT2a agonists could be used as effective therapeutic agents to treat drug addiction. These findings could explain the neurobiological correlate of the therapeutic use of 5HT2a agonists, which can be found in animals, plants and fungi during traditional medicine ceremonies and rituals to treat mood related disorders.

Upregulation of Ca2+-binding proteins contributes to VTA dopamine neuron survival in the early phases of Alzheimer's disease in Tg2576 mice.

BACKGROUND: Recent clinical and experimental studies have highlighted the involvement of Ventral Tegmental Area (VTA) dopamine (DA) neurons for the early pathogenesis of Alzheimer's Disease (AD). We have previously described a progressive and selective degeneration of these neurons in the Tg2576 mouse model of AD, long before amyloid-beta plaque formation. The degenerative process in DA neurons is associated with an autophagy flux impairment, whose rescue can prevent neuronal loss. Impairments in autophagy can be the basis for accumulation of damaged mitochondria, leading to disturbance in calcium (Ca2+) homeostasis, and to functional and structural deterioration of DA neurons. METHODS: In Tg2576 mice, we performed amperometric recordings of DA levels and analysis of dopaminergic fibers in the Nucleus Accumbens - a major component of the ventral striatum precociously affected in AD patients - together with retrograde tracing, to identify the most vulnerable DA neuron subpopulations in the VTA. Then, we focused on these neurons to analyze mitochondrial integrity and Apoptosis-inducing factor (AIF) localization by electron and confocal microscopy, respectively. Stereological cell count was also used to evaluate degeneration of DA neuron subpopulations containing the Ca2+-binding proteins Calbindin-D28K and Calretinin. The expression levels for these proteins were analyzed by western blot and confocal microscopy. Lastly, using electrophysiology and microfluorometry we analyzed VTA DA neuron intrinsic properties and cytosolic free Ca2+ levels. RESULTS: We found a progressive degeneration of mesolimbic DA neurons projecting to the ventral striatum, located in the paranigral nucleus and parabrachial pigmented subnucleus of the VTA. At the onset of degeneration (3 months of age), the vulnerable DA neurons in the Tg2576 accumulate damaged mitochondria, while AIF translocates from the mitochondria to the nucleus. Although we describe an age-dependent loss of the DA neurons expressing Calbindin-D28K or Calretinin, we observed that the remaining cells upregulate the levels of Ca2+-binding proteins, and the free cytosolic levels of Ca2+ in these neurons are significantly decreased. Coherently, TUNEL-stained Tg2576 DA neurons express lower levels of Calbindin-D28K when compared with non-apoptotic cells. CONCLUSION: Overall, our results suggest that the overexpression of Ca2+-binding proteins in VTA DA neurons might be an attempt of cells to survive by increasing their ability to buffer free Ca2+. Exploring strategies to overexpress Ca2+-binding proteins could be fundamental to reduce neuronal suffering and improve cognitive and non-cognitive functions in AD.

Sox6 expression distinguishes dorsally and ventrally biased dopamine neurons in the substantia nigra with distinctive properties and embryonic origins.

Dopamine (DA) neurons in the ventral tier of the substantia nigra pars compacta (SNc) degenerate prominently in Parkinson's disease, while those in the dorsal tier are relatively spared. Defining the molecular, functional, and developmental characteristics of each SNc tier is crucial to understand their distinct susceptibility. We demonstrate that Sox6 expression distinguishes ventrally and dorsally biased DA neuron populations in the SNc. The Sox6+ population in the ventral SNc includes an Aldh1a1+ subset and is enriched in gene pathways that underpin vulnerability. Sox6+ neurons project to the dorsal striatum and show activity correlated with acceleration. Sox6- neurons project to the medial, ventral, and caudal striatum and respond to rewards. Moreover, we show that this adult division is encoded early in development. Overall, our work demonstrates a dual origin of the SNc that results in DA neuron cohorts with distinct molecular profiles, projections, and functions.

The transcription factor BCL11A defines distinct subsets of midbrain dopaminergic neurons.

Midbrain dopaminergic (mDA) neurons are diverse in their projection targets, effect on behavior, and susceptibility to neurodegeneration. Little is known about the molecular mechanisms establishing this diversity during development. We show that the transcription factor BCL11A is expressed in a subset of mDA neurons in the developing and adult murine brain and in a subpopulation of pluripotent-stem-cell-derived human mDA neurons. By combining intersectional labeling and viral-mediated tracing, we demonstrate that Bcl11a-expressing mDA neurons form a highly specific subcircuit within the murine dopaminergic system. In the substantia nigra, the Bcl11a-expressing mDA subset is particularly vulnerable to neurodegeneration upon α-synuclein overexpression or oxidative stress. Inactivation of Bcl11a in murine mDA neurons increases this susceptibility further, alters the distribution of mDA neurons, and results in deficits in skilled motor behavior. In summary, BCL11A defines mDA subpopulations with highly distinctive characteristics and is required for establishing and maintaining their normal physiology.

Endoplasmic Reticulum Stress Is Associated with the Mesencephalic Dopaminergic Neuron Injury in Stressed Rats.

An increasing number of people are in a state of stress due to social and psychological pressures, which may result in mental disorders. Previous studies indicated that mesencephalic dopaminergic neurons are associated with not only reward-related behaviors but also with stress-induced mental disorders. To explore the effect of stress on dopaminergic neuron and potential mechanism, we established stressed rat models of different time durations and observed pathological changes in dopaminergic neurons of the ventral tegmental area (VTA) through HE and thionine staining. Immunohistochemistry coupled with microscopy-based multicolor tissue cytometry (MMTC) was employed to investigate the number changes of dopaminergic neurons. Double immunofluorescence labelling was used to investigate expression changes of endoplasmic reticulum stress (ERS) protein GRP78 and CHOP in dopaminergic neurons. Our results showed that prolonged stress led to pathological alteration in dopaminergic neurons of VTA, such as missing of Nissl bodies and pyknosis in dopaminergic neurons. Immunohistochemistry with MMTC indicated that chronic stress exposure resulted in a significant decrease in dopaminergic neurons. Double immunofluorescence labelling showed that the endoplasmic reticulum stress protein took part in the injury of dopaminergic neurons. Taken together, these results indicated the involvement of ERS in mesencephalic dopaminergic neuron injury induced by stress exposure.

Precise Ultrasound Neuromodulation in a Deep Brain Region Using Nano Gas Vesicles as Actuators.

Ultrasound is a promising new modality for non-invasive neuromodulation. Applied transcranially, it can be focused down to the millimeter or centimeter range. The ability to improve the treatment's spatial resolution to a targeted brain region could help to improve its effectiveness, depending upon the application. The present paper details a neurostimulation scheme using gas-filled nanostructures, gas vesicles (GVs), as actuators for improving the efficacy and precision of ultrasound stimuli. Sonicated primary neurons display dose-dependent, repeatable Ca2+ responses, closely synced to stimuli, and increased nuclear expression of the activation marker c-Fos in the presence of GVs. GV-mediated ultrasound triggered rapid and reversible Ca2+ responses in vivo and could selectively evoke neuronal activation in a deep-seated brain region. Further investigation indicate that mechanosensitive ion channels are important mediators of this effect. GVs themselves and the treatment scheme are also found not to induce significant cytotoxicity, apoptosis, or membrane poration in treated cells. Altogether, this study demonstrates a simple and effective method to achieve enhanced and better-targeted neurostimulation with non-invasive low-intensity ultrasound.

Downregulation of astroglial glutamate transporter GLT-1 in the lateral habenula is associated with depressive-like behaviors in a rat model of Parkinson's disease.

Recent studies show that neuron-glial communication plays an important role in neurological diseases. Particularly, dysfunction of astroglial glutamate transporter GLT-1 has been involved in various neuropsychiatric disorders, including Parkinson's disease (PD) and depression. Our previous studies indicated hyperactivity of neurons in the lateral habenula (LHb) of hemiparkinsonian rats with depressive-like behaviors. Thus, we hypothesized that impaired expression or function of GLT-1 in the LHb might be a potential contributor to LHb hyperactivity, which consequently induces PD-related depression. In the study, unilateral lesions of the substantia nigra pars compacta (SNc) by 6-hydroxydopamine in rats induced depressive-like behaviors and resulted in neuronal hyperactivity as well as increased glutamate levels in the LHb compared to sham-lesioned rats. Intra-LHb injection of GLT-1 inhibitor WAY-213613 induced the depressive-like behaviors in both groups, but the dose producing behavioral effects in the lesioned rats was lower than that of sham-lesioned rats. In the two groups of rats, WAY-213613 increased the firing rate of LHb neurons and extracellular levels of glutamate, and these excitatory effects in the lesioned rats lasted longer than those in sham-lesioned rats. The functional changes of the GLT-1 which primarily expresses in astrocytes in the LHb may attribute to its downregulation after degeneration of the nigrostriatal pathway. Bioinformatics analysis showed that GLT-1 is correlated with various biomarkers of PD and depression risks. Collectively, our study suggests that astroglial GLT-1 in the LHb regulates the firing activity of the neurons, whereupon its downregulation and dysfunction are closely associated with PD-related depression.

Dopaminergic brainstem disconnection is common to pharmacological and pathological consciousness perturbation.

Clinical research into consciousness has long focused on cortical macroscopic networks and their disruption in pathological or pharmacological consciousness perturbation. Despite demonstrating diagnostic utility in disorders of consciousness (DoC) and monitoring anesthetic depth, these cortico-centric approaches have been unable to characterize which neurochemical systems may underpin consciousness alterations. Instead, preclinical experiments have long implicated the dopaminergic ventral tegmental area (VTA) in the brainstem. Despite dopaminergic agonist efficacy in DoC patients equally pointing to dopamine, the VTA has not been studied in human perturbed consciousness. To bridge this translational gap between preclinical subcortical and clinical cortico-centric perspectives, we assessed functional connectivity changes of a histologically characterized VTA using functional MRI recordings of pharmacologically (propofol sedation) and pathologically perturbed consciousness (DoC patients). Both cohorts demonstrated VTA disconnection from the precuneus and posterior cingulate (PCu/PCC), a main default mode network node widely implicated in consciousness. Strikingly, the stronger VTA-PCu/PCC connectivity was, the more the PCu/PCC functional connectome resembled its awake configuration, suggesting a possible neuromodulatory relationship. VTA-PCu/PCC connectivity increased toward healthy control levels only in DoC patients who behaviorally improved at follow-up assessment. To test whether VTA-PCu/PCC connectivity can be affected by a dopaminergic agonist, we demonstrated in a separate set of traumatic brain injury patients without DoC that methylphenidate significantly increased this connectivity. Together, our results characterize an in vivo dopaminergic connectivity deficit common to reversible and chronic consciousness perturbation. This noninvasive assessment of the dopaminergic system bridges preclinical and clinical work, associating dopaminergic VTA function with macroscopic network alterations, thereby elucidating a critical aspect of brainstem-cortical interplay for consciousness.

Prenatal THC Does Not Affect Female Mesolimbic Dopaminergic System in Preadolescent Rats.

Cannabis use among pregnant women is increasing worldwide along with permissive sociocultural attitudes toward it. Prenatal cannabis exposure (PCE), however, is associated with adverse outcome among offspring, ranging from reduced birth weight to child psychopathology. We have previously shown that male rat offspring prenatally exposed to Δ9-tetrahydrocannabinol (THC), a rat model of PCE, exhibit extensive molecular, cellular, and synaptic changes in dopamine neurons of the ventral tegmental area (VTA), resulting in a susceptible mesolimbic dopamine system associated with a psychotic-like endophenotype. This phenotype only reveals itself upon a single exposure to THC in males but not females. Here, we characterized the impact of PCE on female behaviors and mesolimbic dopamine system function by combining in vivo single-unit extracellular recordings in anesthetized animals and ex vivo patch clamp recordings, along with neurochemical and behavioral analyses. We find that PCE female offspring do not show any spontaneous or THC-induced behavioral disease-relevant phenotypes. The THC-induced increase in dopamine levels in nucleus accumbens was reduced in PCE female offspring, even when VTA dopamine activity in vivo and ex vivo did not differ compared to control. These findings indicate that PCE impacts mesolimbic dopamine function and its related behavioral domains in a sex-dependent manner and warrant further investigations to decipher the mechanisms determining this sex-related protective effect from intrauterine THC exposure.

Maternal separation increases cocaine intake through a mechanism involving plasticity in glutamate signalling.

Early-life stress (ELS) is associated with negative consequences, including maladaptive long-lasting brain effects. These alterations seem to increase the likelihood of developing substance use disorders. However, the molecular consequences of ELS are poorly understood. In the present study, we tested the impact of ELS induced by maternal separation with early weaning (MSEW) in CD1 male mice at different phases of cocaine self-administration (SA). We also investigated the subsequent alterations on GluR2, GluR1, cAMP response element-binding (CREB), and CREB-phosphorylation (pCREB) in ventral tegmental area (VTA) and nucleus accumbens (NAc) induced by both MSEW and cocaine SA. Our results show that MSEW animals expressed a higher cocaine intake, an increased vulnerability to the acquisition of cocaine SA, and incapacity to extinguish cocaine SA behaviour. MSEW mice showed decreased GluR2 and increased GluR1 and pCREB in NAc. Also, results displayed reduction of basal levels of GluR1 and CREB and an elevation of GluR1/GluR2 ratio in the VTA. Such results hint at an enhanced glutamatergic function in NAc and increased excitability of VTA DA neurons in maternally separated mice. Altogether, our results suggest that MSEW induces molecular alterations in the brain areas related to reward processing, increasing the vulnerability to depression and cocaine-seeking behaviour.

Behavioral effects of SGK1 knockout in VTA and dopamine neurons.

Drugs of abuse cause significant neuroadaptations within the ventral tegmental area (VTA), with alterations in gene expression tied to changes in reward behavior. Serum- and glucocorticoid-inducible kinase 1 (SGK1) transcription, catalytic activity, and phosphorylation are upregulated in the VTA by chronic cocaine or morphine treatment, positioning SGK1 as a critical mediator of reward behavior. Using transgenic mouse models, we investigated the effect of SGK1 knockout in the VTA and in dopamine (DA) neurons to evaluate the necessity of protein expression for natural and drug reward behaviors. SGK1 knockdown in the VTA did not impact reward behaviors. Given VTA cellular heterogeneity, we also investigated a DA neuron-specific SGK1 knockout (KO). DA SGK1 KO significantly decreased body weight of adult mice as well as increased general locomotor activity; however, reward behaviors were similarly unaltered. Given that SGK1 mutants virally overexpressed in the VTA are capable of altering drug-associated behavior, our current results suggest that changes in SGK1 protein signaling may be distinct from expression. This work yields novel information on the impact of SGK1 deletion, critical for understanding the role of SGK1 signaling in the central nervous system and evaluating SGK1 as a potential therapeutic target for treatment of substance use disorders.

Computational Modeling of Catecholamines Dysfunction in Alzheimer's Disease at Pre-Plaque Stage.

BACKGROUND: Alzheimer's disease (AD) etiopathogenesis remains partially unexplained. The main conceptual framework used to study AD is the Amyloid Cascade Hypothesis, although the failure of recent clinical experimentation seems to reduce its potential in AD research. OBJECTIVE: A possible explanation for the failure of clinical trials is that they are set too late in AD progression. Recent studies suggest that the ventral tegmental area (VTA) degeneration could be one of the first events occurring in AD progression (pre-plaque stage). METHODS: Here we investigate this hypothesis through a computational model and computer simulations validated with behavioral and neural data from patients. RESULTS: We show that VTA degeneration might lead to system-level adjustments of catecholamine release, triggering a sequence of events leading to relevant clinical and pathological signs of AD. These changes consist first in a midfrontal-driven compensatory hyperactivation of both VTA and locus coeruleus (norepinephrine) followed, with the progression of the VTA impairment, by a downregulation of catecholamine release. These processes could then trigger the neural degeneration at the cortical and hippocampal levels, due to the chronic loss of the neuroprotective role of norepinephrine. CONCLUSION: Our novel hypothesis might contribute to the formulation of a wider system-level view of AD which might help to devise early diagnostic and therapeutic interventions.

Fetal growth restriction mice are more likely to exhibit depression-like behaviors due to stress-induced loss of dopaminergic neurons in the VTA.

Fetal growth restriction (FGR) is a severe perinatal complication that can increase risk for mental illness. To investigate the mechanism by which FGR mice develop mental illness in adulthood, we established the FGR mouse model and the FGR mice did not display obvious depression-like behaviors, but after environmental stress exposure, FGR mice were more likely to exhibit depression-like behaviors than control mice. Moreover, FGR mice had significantly fewer dopaminergic neurons in the ventral tegmental area but no difference in serotoninergic neurons in the dorsal raphe. RNA-seq analysis showed that the downregulated genes in the midbrain of FGR mice were associated with many mental diseases and were especially involved in the regulation of NMDA-selective glutamate receptor (NMDAR) activity. Furthermore, the NMDAR antagonist memantine can relieve the stress-induced depression-like behaviors of FGR mice. In summary, our findings provide a theoretical basis for future research and treatment of FGR-related depression.

Toxicological effects of propofol abuse on the dopaminergic neurons in ventral tegmental area and corpus striatum and its potential mechanisms.

This study was aimed at examining propofol- (a known anesthetic) induced emotion-related behavioral disorders in mice, and exploring the possible molecular mechanisms. A total of 60 mice were divided into two groups: control and propofol group. Mice were injected with propofol (150 mg/kg, ip) at 8:00 a.m. (once a day, lasting for 30 days). During the 30 days, loss of righting reflex (LORR) and return of righting reflex (RORR) of mice were recorded every day. At the 1st (T1) and 30th (T2) day of drug discontinuance (T2), 15 mice of each group were selected to perform the open field test; then the mice underwent perfusion fixation, and the midbrain and corpus striatum were separated for immunofluorescence assay with anti-tyrosine hydroxylase (Th) and anti- dopamine transporter (DAT) antibodies. Results showed that after propofol injection, LORR and RORR increased and decreased, respectively. Long-term use of propofol resulted in decreased activities of mice (activity trajectory, line crossing, rearing time, scratching times and defecating frequency). Immunofluorescence assay showed long-term use of propofol induced decrease of Th and DAT. Collectively, our present work suggested long-term abuse of propofol induces neuropsychiatric function impairments, and the possible mechanisms are related to dopamine dyssynthesis via down-regulating tyrosine hydroxylase and dopamine transporter.

Nigral and ventral tegmental area lesioning induces testicular and sperm morphological abnormalities in a rotenone model of Parkinson's disease.

Although sexual health is affected by Parkinson's disease (PD), the effect on testicular health and/or sperm quality is not well discussed. After 21 days of rotenone lesioning, we observed dopaminergic neuronal degeneration in the substantia nigra and hypothalamus. There were minimal SPACA-1-expressing epididymal spermatozoa with morphological abnormalities, scanty luminal spermatozoa and reduced testicular spermatids and post-meiotic germ cells indicating hypospermatogenesis. Occludin-expressing sertoli cells were dispersed over a wide area indicating compromised blood-testes barrier. Activated caspase-3 expression was intense while immunoreactivity of spermatogenic-enhancing SRY and GADD45 g was weak. Although serum follicle stimulating hormone level was not affected, the lesion was associated with reduced serum testosterone level, testicular oxidative damage and inhibition of acetylcholinesterase activity, even when rotenone was not detected in the testes. Together, dopaminergic lesions may mediate testicular and sperm abnormalities via the brain-hypothalamic-testicular circuit independent of the pituitary, thereby establishing a causal link between Parkinsonism and reproductive dysfunction.

A mutant vesicular stomatitis virus with reduced cytotoxicity and enhanced anterograde trans-synaptic efficiency.

Understanding the connecting structure of brain network is the basis to reveal the principle of the brain function and elucidate the mechanism of brain diseases. Trans-synaptic tracing with neurotropic viruses has become one of the most effective technologies to dissect the neural circuits. Although the retrograde trans-synaptic tracing for analyzing the input neural networks with recombinant rabies and pseudorabies virus has been broadly applied in neuroscience, viral tools for analyzing the output neural networks are still lacking. The recombinant vesicular stomatitis virus (VSV) has been used for the mapping of synaptic outputs. However, several drawbacks, including high neurotoxicity and rapid lethality in experimental animals, hinder its application in long-term studies of the structure and function of neural networks. To overcome these limitations, we generated a recombinant VSV with replication-related N gene mutation, VSV-NR7A, and examined its cytotoxicity and efficiency of trans-synaptic spreading. We found that by comparison with the wild-type tracer of VSV, the NR7A mutation endowed the virus lower rate of propagation and cytotoxicity in vitro, as well as significantly reduced neural inflammatory responses in vivo and much longer animal survival when it was injected into the nucleus of the mice brain. Besides, the spreading of the attenuated VSV was delayed when injected into the VTA. Importantly, with the reduced toxicity and extended animal survival, the number of brain regions that was trans-synaptically labeled by the mutant VSV was more than that of the wild-type VSV. These results indicated that the VSV-NR7A, could be a promising anterograde tracer that enables researchers to explore more downstream connections of a given brain region, and observe the anatomical structure and the function of the downstream circuits over a longer time window. Our work could provide an improved tool for structural and functional studies of neurocircuit.

Human-Specific Transcriptome of Ventral and Dorsal Midbrain Dopamine Neurons.

OBJECTIVE: Neuronal loss in the substantia nigra pars compacta (SNpc) in Parkinson disease (PD) is not uniform, as dopamine neurons from the ventral tier are lost more rapidly than those of the dorsal tier. Identifying the intrinsic differences that account for this differential vulnerability may provide a key for developing new treatments for PD. METHODS: Here, we compared the RNA-sequenced transcriptomes of ~100 laser captured microdissected SNpc neurons from each tier from 7 healthy controls. RESULTS: Expression levels of dopaminergic markers were similar across the tiers, whereas markers specific to the neighboring ventral tegmental area were virtually undetected. After accounting for unwanted sources of variation, we identified 106 differentially expressed genes (DEGs) between the SNpc tiers. The genes higher in the dorsal/resistant SNpc tier neurons displayed coordinated patterns of expression across the human brain, their protein products had more interactions than expected by chance, and they demonstrated evidence of functional convergence. No significant shared functionality was found for genes higher in the ventral/vulnerable SNpc tier. Surprisingly but importantly, none of the identified DEGs was among the familial PD genes or genome-wide associated loci. Finally, we found some DEGs in opposite tier orientation between human and analogous mouse populations. INTERPRETATION: Our results highlight functional enrichments of vesicular trafficking, ion transport/homeostasis and oxidative stress genes showing higher expression in the resistant neurons of the SNpc dorsal tier. Furthermore, the comparison of gene expression variation in human and mouse SNpc populations strongly argues for the need of human-focused omics studies. ANN NEUROL 2020;87:853-868.

Mitochondrial Dysfunction Combined with High Calcium Load Leads to Impaired Antioxidant Defense Underlying the Selective Loss of Nigral Dopaminergic Neurons.

Mitochondrial dysfunction is critically involved in Parkinson's disease, characterized by loss of dopaminergic neurons (DaNs) in the substantia nigra (SNc), whereas DaNs in the neighboring ventral tegmental area (VTA) are much less affected. In contrast to VTA, SNc DaNs engage calcium channels to generate action potentials, which lead to oxidant stress by yet unknown pathways. To determine the molecular mechanisms linking calcium load with selective cell death in the presence of mitochondrial deficiency, we analyzed the mitochondrial redox state and the mitochondrial membrane potential in mice of both sexes with genetically induced, severe mitochondrial dysfunction in DaNs (MitoPark mice), at the same time expressing a redox-sensitive GFP targeted to the mitochondrial matrix. Despite mitochondrial insufficiency in all DaNs, exclusively SNc neurons showed an oxidized redox-system, i.e., a low reduced/oxidized glutathione (GSH-GSSG) ratio. This was mimicked by cyanide, but not by rotenone or antimycin A, making the involvement of reactive oxygen species rather unlikely. Surprisingly, a high mitochondrial inner membrane potential was maintained in MitoPark SNc DaNs. Antagonizing calcium influx into the cell and into mitochondria, respectively, rescued the disturbed redox ratio and induced further hyperpolarization of the inner mitochondrial membrane. Our data therefore show that the constant calcium load in SNc DaNs is counterbalanced by a high mitochondrial inner membrane potential, even under conditions of severe mitochondrial dysfunction, but triggers a detrimental imbalance in the mitochondrial redox system, which will lead to neuron death. Our findings thus reveal a new mechanism, redox imbalance, which underlies the differential vulnerability of DaNs to mitochondrial defects.SIGNIFICANCE STATEMENT Parkinson's disease is characterized by the preferential degeneration of dopaminergic neurons (DaNs) of the substantia nigra pars compacta (SNc), resulting in the characteristic hypokinesia in patients. Ubiquitous pathological triggers cannot be responsible for the selective neuron loss. Here we show that mitochondrial impairment together with elevated calcium burden destabilize the mitochondrial antioxidant defense only in SNc DaNs, and thus promote the increased vulnerability of this neuron population.

A POMC-originated circuit regulates stress-induced hypophagia, depression, and anhedonia.

Chronic stress causes dysregulations of mood and energy homeostasis, but the neurocircuitry underlying these alterations remain to be fully elucidated. Here we demonstrate that chronic restraint stress in mice results in hyperactivity of pro-opiomelanocortin neurons in the arcuate nucleus of the hypothalamus (POMCARH neurons) associated with decreased neural activities of dopamine neurons in the ventral tegmental area (DAVTA neurons). We further revealed that POMCARH neurons project to the VTA and provide an inhibitory tone to DAVTA neurons via both direct and indirect neurotransmissions. Finally, we show that photoinhibition of the POMCARH→VTA circuit in mice increases body weight and food intake, and reduces depression-like behaviors and anhedonia in mice exposed to chronic restraint stress. Thus, our results identified a novel neurocircuitry regulating feeding and mood in response to stress.