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Besides having high potency and efficacy at the µ- (MOR) and other opioid receptor types, fentanyl has some affinity for some adrenergic receptor types, which may underlie its unique pathophysiological differences from typical opioids. To better understand the unique actions of fentanyl, we assessed the extent to which fentanyl alters striatal medium spiny neuronal (MSNs) activity via opioid or α1 adrenoceptors in dopamine type 1 or type 2 receptor- (D1 or D2) -expressing MSNs. In neuronal and mixed-glial co-cultures from the striatum, acute fentanyl (100 nM) exposure decreased the frequency of spontaneous action potentials. Overnight exposure of co-cultures to 100 nM fentanyl severely reduced the proportion of MSNs with spontaneous action potentials, which was unaffected by co-exposure to the opioid receptor antagonist naloxone (10 µM), but fully negated by co-administering the pan-α1 adrenoceptor inverse agonist prazosin (100 nM) and partially reversed by the selective α1A/C adrenoceptor antagonist RS 100329 (300 nM). Acute fentanyl (100 nM) exposure modestly reduced the frequency of action potentials and caused firing rate adaptations in D2, but not D1, MSNs. Prolonged (2-5 h) fentanyl (100 nM) application dramatically attenuated firing rates in both D1 and D2 MSNs. To identify possible cellular sites of α1 adrenoceptor action, α1 adrenoceptors were localized in subpopulations of striatal astroglia and neurons by immunocytochemistry, and Adra1a mRNA by in situ hybridization in astrocytes. Thus, sustained fentanyl exposure can inhibit striatal MSN activity via a non-opioid receptor-dependent pathway, that may be modulated via complex actions in α1 adrenoceptor-expressing striatal neurons and/or glia.
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Opioids produce addictive, analgesic, and euphoric effects via actions at mu opioid receptors (µORs). The µOR is encoded by the Oprm1 gene and is expressed in multiple brain regions that regulate reward and motivation, such as the nucleus accumbens (NAc). Oprm1 expression in NAc medium spiny neurons (MSNs) mediates opioid place preference, seeking, and consumption. However, recent single nucleus RNA sequencing (snRNA-seq) studies have revealed that multiple subpopulations of NAc neurons express Oprm1 mRNA, making it unclear which populations mediate diverse behaviors resulting from µOR activation. Using published snRNA-seq datasets from the rat NAc, we identified a novel population of MSNs that express the highest levels of Oprm1 of any NAc cell type. Here, we show that this population is selectively marked by expression of Chst9, a gene encoding a carbohydrate sulfotransferase. Notably, Chst9+ neurons exhibited more abundant expression of Oprm1 as compared to other cell types, and formed discrete cellular clusters along the medial and ventral borders of the NAc shell subregion. Moreover, CHST9 mRNA was also found to mark specific MSN populations in published human and primate snRNA-seq studies, indicating that this unique population may be conserved across species. Together, these results identify a spatially and transcriptionally distinct NAc neuron population characterized by the expression of Chst9. The abundant expression of Oprm1 in this population and the conservation of these cells across species suggests that they may play a key functional role in opioid response and identify this subpopulation as a target for further investigation.
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Approaches for the induction of neurogenesis and neuronal recovery through several modalities are gaining popularity in Parkinson's disease (PD). Growth hormone (GH) seems to have a role in the reversal of neural function following brain injury as well as in normal brain development and function; therefore, the use of GH may represent a feasible strategy in the management of PD. This experimental study aimed to evaluate the effect of growth hormone on motor function and dendrite morphology in rats with 6-hydroxydopamine (6-OHDA)-induced PD model. Thirty-six Sprague Dawley rats were included and randomly allocated into one of the six study groups: two controls and four treatment groups that received daily subcutaneous growth hormone injections for 21 days, 1, 2, and 3 months. PD model was induced through unilateral 6-OHDA injection to the nigrostriatal pathway. The following assessments were made: apomorphine rotation test, stepping test, and tissue examinations for tyrosine hydroxylase and dendrite morphology. The apomorphine rotation test and the stepping test confirmed the presence of PD. These tests as well as dendritic spine density/number and length assessments showed improvement in PD findings over time with GH administration. Findings of this study suggest that GH administration may improve dendrite morphology and motor function in the PD model, which may translate into symptom relief and quality of life improvement in patients with PD. Such potential benefits should be tested in robust clinical studies.
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Rhes (Ras homolog enriched in the striatum), a multifunctional protein that regulates striatal functions associated with motor behaviors and neurological diseases, can shuttle from cell to cell via the formation of tunneling-like nanotubes (TNTs). However, the mechanisms by which Rhes mediates diverse functions remain unclear. Rhes is a small GTPase family member which contains a unique C-terminal Small Ubiquitin-like Modifier (SUMO) E3-like domain that promotes SUMO post-translational modification of proteins (SUMOylation) by promoting "cross-SUMOylation" of the SUMO enzyme SUMO E1 (Aos1/Uba2) and SUMO E2 ligase (Ubc-9). Nevertheless, the identity of the SUMO substrates of Rhes remains largely unknown. Here, by combining high throughput interactome and SUMO proteomics, we report that Rhes regulates the SUMOylation of nuclear proteins that are involved in the regulation of gene expression. Rhes increased the SUMOylation of histone deacetylase 1 (HDAC1) and histone 2B, while decreasing SUMOylation of heterogeneous nuclear ribonucleoprotein M (HNRNPM), protein polybromo-1 (PBRM1) and E3 SUMO-protein ligase (PIASy). We also found that Rhes itself is SUMOylated at 6 different lysine residues (K32, K110, K114, K120, K124, and K245). Furthermore, Rhes regulated the expression of genes involved in cellular morphogenesis and differentiation in the striatum, in a SUMO-dependent manner. Our findings thus provide evidence for a previously undescribed role for Rhes in regulating the SUMOylation of nuclear targets and in orchestrating striatal gene expression via SUMOylation.
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Proteínas Nucleares , Ubiquitina , Ubiquitina/metabolismo , Proteínas Nucleares/metabolismo , Processamento de Proteína Pós-Traducional , Ubiquitina-Proteína Ligases/genética , Ubiquitina-Proteína Ligases/metabolismo , Ubiquitinas/genética , Sumoilação , Expressão Gênica , Proteínas Modificadoras Pequenas Relacionadas à Ubiquitina/metabolismoRESUMO
BACKGROUND: Different neural subtypes are selectively lost in diverse neurodegenerative diseases. Huntington's disease (HD) is an inherited neurodegenerative disease characterized by motor abnormalities that primarily affect the striatum. The Huntingtin (HTT) mutation involves an expanded CAG repeat, leading to insoluble polyQ, which renders GABA+ medium spiny neurons (MSN) more venerable to cell death. Human pluripotent stem cells (hPSCs) technology allows for the construction of disease-specific models, providing valuable cellular models for studying pathogenesis, drug screening, and high-throughput analysis. METHODS: In this study, we established a method that allows for rapid and efficient generation of MSNs (> 90%) within 21 days from hPSC-derived neural progenitor cells, by introducing a specific combination of transcription factors. RESULTS: We efficiently induced several neural subtypes, in parallel, based on the same cell source, and revealed that, compared to other neural subtypes, MSNs exhibited higher polyQ aggregation propensity and overexpression toxicity, more severe dysfunction in BDNF/TrkB signaling, greater susceptibility to BDNF withdrawal, and more severe disturbances in nucleocytoplasmic transport (NCT). We further found that the nuclear lamina protein LMNB1 was greatly reduced in HD neurons and mislocalized to the cytoplasm and axons. Knockdown of HTT or treatment with KPT335, an orally selective inhibitor of nuclear export (SINE), effectively attenuated the pathological phenotypes and alleviated neuronal death caused by BDNF withdrawal. CONCLUSIONS: This study thus establishes an effective method for obtaining MSNs and underscores the necessity of using high-purity MSNs to study HD pathogenesis, especially the MSN-selective vulnerability.
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Alcohol use disorder (AUD) requires new neurobiological targets. Problematic drinking involves underactive indirect pathway medium spiny neurons (iMSNs) that subserve adaptive behavioral selection vs. overactive direct pathway MSNs (dMSNs) that promote drinking, with a shift from ventromedial to dorsolateral striatal (VMS, DLS) control of EtOH-related behavior. We hypothesized that inhibiting phosphodiesterase 10A (PDE10A), enriched in striatal MSNs, would reduce EtOH self-administration in rats with a history of chronic intermittent ethanol exposure. To test this, Wistar rats (n = 10/sex) with a history of chronic intermittent EtOH (CIE) vapor exposure received MR1916 (i.p., 0, 0.05, 0.1, 0.2, and 0.4 µmol/kg), a PDE10A inhibitor, before operant EtOH self-administration sessions. We determined whether MR1916 altered the expression of MSN markers (Pde10a, Drd1, Drd2, Penk, and Tac1) and immediate-early genes (IEG) (Fos, Fosb, ΔFosb, and Egr1) in EtOH-naïve (n = 5-6/grp) and post-CIE (n = 6-8/grp) rats. MR1916 reduced the EtOH self-administration of high-drinking, post-CIE males, but increased it at a low, but not higher, doses, in females and low-drinking males. MR1916 increased Egr1, Fos, and FosB in the DLS, modulated by sex and alcohol history. MR1916 elicited dMSN vs. iMSN markers differently in ethanol-naïve vs. post-CIE rats. High-drinking, post-CIE males showed higher DLS Drd1 and VMS IEG expression. Our results implicate a role and potential striatal bases of PDE10A inhibitors to influence post-dependent drinking.
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Etanol , Compostos Orgânicos , Inibidores de Fosfodiesterase , Masculino , Feminino , Ratos , Animais , Etanol/farmacologia , Inibidores de Fosfodiesterase/farmacologia , Inibidores de Fosfodiesterase/uso terapêutico , Ratos Wistar , Diester Fosfórico Hidrolases/genética , Diester Fosfórico Hidrolases/metabolismo , Expressão GênicaRESUMO
Response to threatening environmental stimuli requires detection and encoding of important environmental features that dictate threat. Aversive events are highly salient, which promotes associative learning about stimuli that signal this threat. The nucleus accumbens is uniquely positioned to process this salient, aversive information and promote motivated output, through plasticity on the major projection neurons in the brain area. We describe a nucleus accumbens core local circuit whereby excitatory plasticity facilitates learning and recall of discrete aversive cues. We demonstrate that putative nucleus accumbens substance P release and long-term excitatory plasticity on dopamine 2 receptor-expressing projection neurons are required for cue-dependent fear learning. Additionally, we find that fear learning and recall is dependent on distinct projection neuron subtypes. Our work demonstrates a critical role for nucleus accumbens substance P in cue-dependent aversive learning.
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Sinais (Psicologia) , Núcleo Accumbens , Núcleo Accumbens/fisiologia , Aprendizagem da Esquiva , Substância P , Receptores DopaminérgicosRESUMO
The dorsal striatum is organized into functional territories defined by corticostriatal inputs onto both direct and indirect spiny projection neurons (SPNs), the major cell types within the striatum. In addition to circuit connectivity, striatal domains are likely defined by the spatially determined transcriptomes of SPNs themselves. To identify cell-type-specific spatiomolecular signatures of direct and indirect SPNs within dorsomedial, dorsolateral, and ventrolateral dorsal striatum, we used RNA profiling in situ hybridization with probes to >98% of protein coding genes. We demonstrate that the molecular identity of SPNs is mediated by hundreds of differentially expressed genes across territories of the striatum, revealing extraordinary heterogeneity in the expression of genes that mediate synaptic function in both direct and indirect SPNs. This deep insight into the complex spatiomolecular organization of the striatum provides a foundation for understanding both normal striatal function and for dissecting region-specific dysfunction in disorders of the striatum.
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Corpo Estriado , Interneurônios , Camundongos , Animais , Camundongos Transgênicos , Corpo Estriado/metabolismo , Neostriado , NeuritosRESUMO
Dyskinesia is involuntary movement caused by long-term medication with dopamine-related agents: the dopamine agonist 3,4-dihydroxy-L-phenylalanine (L-DOPA) to treat Parkinson's disease (L-DOPA-induced dyskinesia [LID]) or dopamine antagonists to treat schizophrenia (tardive dyskinesia [TD]). However, it remains unknown why distinct types of medications for distinct neuropsychiatric disorders induce similar involuntary movements. Here, we search for a shared structural footprint using magnetic resonance imaging-based macroscopic screening and super-resolution microscopy-based microscopic identification. We identify the enlarged axon terminals of striatal medium spiny neurons in LID and TD model mice. Striatal overexpression of the vesicular gamma-aminobutyric acid transporter (VGAT) is necessary and sufficient for modeling these structural changes; VGAT levels gate the functional and behavioral alterations in dyskinesia models. Our findings indicate that lowered type 2 dopamine receptor signaling with repetitive dopamine fluctuations is a common cause of VGAT overexpression and late-onset dyskinesia formation and that reducing dopamine fluctuation rescues dyskinesia pathology via VGAT downregulation.
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Discinesia Induzida por Medicamentos , Transtornos Parkinsonianos , Camundongos , Animais , Agonistas de Dopamina/efeitos adversos , Levodopa/efeitos adversos , Dopamina , Antiparkinsonianos/efeitos adversos , Transtornos Parkinsonianos/induzido quimicamente , Transtornos Parkinsonianos/patologia , Discinesia Induzida por Medicamentos/etiologia , Discinesia Induzida por Medicamentos/tratamento farmacológico , Discinesia Induzida por Medicamentos/patologia , Oxidopamina/efeitos adversos , Ácido gama-Aminobutírico/efeitos adversosRESUMO
Learning action sequences is necessary for normal daily activities. Medium spiny neurons (MSNs) in the dorsal striatum (dStr) encode action sequences through changes in firing at the start and/or stop of action sequences or sustained changes in firing throughout the sequence. Acetylcholine (ACh), released from cholinergic interneurons (ChIs), regulates striatal function by modulating MSN and interneuron excitability, dopamine and glutamate release, and synaptic plasticity. Cholinergic neurons in dStr pause their tonic firing during the performance of learned action sequences. Activation of dopamine type-2 receptors (D2Rs) on ChIs is one mechanism of ChI pausing. In this study we show that deleting D2Rs from ChIs by crossing D2-floxed with ChAT-Cre mice (D2Flox-ChATCre), which inhibits dopamine-mediated ChI pausing and leads to deficits in an operant action sequence task and lower breakpoints in a progressive ratio task. These data suggest that D2Flox-ChATCre mice have reduced motivation to work for sucrose reward, but show no generalized motor skill deficits. D2Flox-ChATCre mice perform similarly to controls in a simple reversal learning task, indicating normal behavioral flexibility, a cognitive function associated with ChIs. In vivo electrophysiological recordings show that D2Flox-ChatCre mice have deficits in sequence encoding, with fewer dStr MSNs encoding entire action sequences compared to controls. Thus, ChI D2R deletion appears to impair a neural substrate of action chunking. Virally replacing D2Rs in dStr ChIs in adult mice improves action sequence learning, but not the lower breakpoints, further suggesting that D2Rs on ChIs in the dStr are critical for sequence learning, but not for driving the motivational aspects of the task.
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Background: Striatal medium spiny neurons (MSNs) are preferentially lost in Huntington's disease. Genomic studies also implicate a direct role for MSNs in schizophrenia, a psychiatric disorder known to involve cortical neuron dysfunction. It remains unknown whether the two diseases share similar MSN pathogenesis or if neuronal deficits can be attributed to cell type-dependent biological pathways. Transcription factor BCL11B, which is expressed by all MSNs and deep layer cortical neurons, was recently proposed to drive selective neurodegeneration in Huntington's disease and identified as a candidate risk gene in schizophrenia. Methods: Using human stem cell-derived neurons lacking BCL11B as a model, we investigated cellular pathology in MSNs and cortical neurons in the context of these disorders. Integrative analyses between differentially expressed transcripts and published genome-wide association study datasets identified cell type-specific disease-related phenotypes. Results: We uncover a role for BCL11B in calcium homeostasis in both neuronal types, while deficits in mitochondrial function and PKA (protein kinase A)-dependent calcium transients are detected only in MSNs. Moreover, BCL11B-deficient MSNs display abnormal responses to glutamate and fail to integrate dopaminergic and glutamatergic stimulation, a key feature of striatal neurons in vivo. Gene enrichment analysis reveals overrepresentation of disorder risk genes among BCL11B-regulated pathways, primarily relating to cAMP-PKA-calcium signaling axis and synaptic signaling. Conclusions: Our study indicates that Huntington's disease and schizophrenia are likely to share neuronal pathophysiology where dysregulation of intracellular calcium homeostasis is found in both striatal and cortical neurons. In contrast, reduction in PKA signaling and abnormal dopamine/glutamate receptor signaling is largely specific to MSNs.
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Transcriptomic responses to neurotransmitters contribute to the complex processes driving memory and addiction. Advances in both measurement methods and experimental models continue to improve our understanding of this regulatory layer. Here we focus on the experimental potential of stem cell derived neurons, currently the only ethical model that can be used in reductionist and experimentally perturbable studies of human cells. Prior work has focused on generating distinct cell types from human stem cells, and has also shown their utility in modeling development and cellular phenotypes related to neurodegeneration. Here we seek an understanding of how stem cell derived neural cultures respond to perturbations experienced during development and disease progression. This work profiles transcriptomic responses of human medium spiny neuron-like cells with three specific goals. We first characterize transcriptomic responses to dopamine and dopamine receptor agonists and antagonists presented in dosing patterns mimicking acute, chronic, and withdrawal regimens. We also assess transcriptomic responses to low and persistent tonic levels of dopamine, acetylcholine, and glutamate to better mimic the in vivo environment. Finally, we identify similar and distinct responses between hMSN-like cells derived from H9 and H1 stem cell lines, providing some context for the extent of variability these types of systems will likely pose for experimentalists. The results here suggest future optimizations of human stem cell derived neurons to increase their in vivo relevance and the biological insights that can be garnered from these models.
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Dopamina , Transcriptoma , Humanos , Dopamina/metabolismo , Neurônios Espinhosos Médios , Neurônios/metabolismo , Células-Tronco/metabolismo , Diferenciação CelularRESUMO
Striatal medium spiny neurons (MSNs) and striatal dopamine (DA) innervation are profoundly important for brain function such as motor control and cognition. A widely accepted theory posits that striatal DA loss causes (or leads to) MSN dendritic atrophy. However, examination of the literature indicates that the data from Parkinson's disease (PD) patients and animal PD models were contradictory among studies and hard to interpret. Here we have re-examined the potential effects of DA activity on MSN morphology or lack thereof. We found that in 15-day, 4- and 12-month old Pitx3 null mutant mice that have severe DA denervation in the dorsal striatum while having substantial residual DA innervation in the ventral striatum, MSN dendrites and spine numbers were similar in dorsal and ventral striatum, and also similar to those in normal mice. In 15-day, 4- and 12-month old tyrosine hydroxylase knockout mice that cannot synthesize L-dopa and thus have no endogenous DA in the entire brain, MSN dendrites and spine numbers were also indistinguishable from age-matched wild-type (WT) mice. Furthermore, in adult WT mice, unilateral 6-OHDA lesion at 12 months of age caused an almost complete striatal DA denervation in the lesioned side, but MSN dendrites and spine numbers were similar in the lesioned and control sides. Taken together, our data indicate that in mice, the development and maintenance of MSN dendrites and spines are DA-independent such that DA depletion does not trigger MSN dendritic atrophy; our data also suggest that the reported MSN dendritic atrophy in PD may be a component of neurodegeneration in PD rather than a consequence of DA denervation.
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Dopamina , Doença de Parkinson , Camundongos , Animais , Dopamina/fisiologia , Neurônios/patologia , Espinhas Dendríticas/patologia , Neurônios Espinhosos Médios , Levodopa/farmacologia , Doença de Parkinson/patologia , Corpo Estriado/patologiaRESUMO
Boosting trophic support to striatal neurons by increasing levels of brain-derived neurotrophic factor (BDNF) has been considered as a target for therapeutic intervention for several neurodegenerative diseases, including Huntington's disease (HD). To aid in the implementation of such a strategy, a thorough understanding of BDNF cortical-striatal transport is critical to help guide its strategic delivery. In this manuscript, we investigate the dynamic behavior of BDNF transport along the cortical-striatal axis in Q140 primary neurons, a mouse model for HD. We examine this by using single-molecule labeling of BDNF conjugated with quantum dots (QD-BDNF) to follow the transport along the cortical-striatal axis in a microfluidic chamber system specifically designed for the co-culture of cortical and striatal primary neurons. Using this approach, we observe a defect of QD-BDNF transport in Q140 neurons. Our study demonstrates that QD-BDNF transport along the cortical-striatal axis involves the impairment of anterograde transport within axons of cortical neurons, and of retrograde transport within dendrites of striatal neurons. One prominent feature we observe is the extended pause time of QD-BDNF retrograde transport within Q140 striatal dendrites. Taken together, these finding support the hypothesis that delinquent spatiotemporal trophic support of BDNF to striatal neurons, driven by impaired transport, may contribute to the pathogenesis of HD, providing us with insight into how a BDNF supplementation therapeutic strategy may best be applied for HD.
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Huntington's disease (HD) is caused by expanded CAG repeats in the huntingtin gene (HTT) resulting in expression of mutant HTT proteins (mHTT) with extended polyglutamine tracts, including in striatal neurons and astrocytes. It is unknown whether pathophysiology in vivo can be attenuated by lowering mHTT in either cell type throughout the brain, and the relative contributions of neurons and astrocytes to HD remain undefined. We use zinc finger protein (ZFP) transcriptional repressors to cell-selectively lower mHTT in vivo. Astrocytes display loss of essential functions such as cholesterol metabolism that are partly driven by greater neuronal dysfunctions, which encompass neuromodulation, synaptic, and intracellular signaling pathways. Using transcriptomics, proteomics, electrophysiology, and behavior, we dissect neuronal and astrocytic contributions to HD pathophysiology. Remarkably, brain-wide delivery of neuronal ZFPs results in strong mHTT lowering, rescue of HD-associated behavioral and molecular phenotypes, and significant extension of lifespan, findings that support translational development.
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Doença de Huntington , Animais , Doença de Huntington/genética , Doença de Huntington/metabolismo , Astrócitos/metabolismo , Proteína Huntingtina/genética , Proteína Huntingtina/metabolismo , Neurônios/metabolismo , Fatores de Transcrição/metabolismo , Dedos de Zinco , Proteínas Mutantes/metabolismo , Modelos Animais de DoençasRESUMO
The ventrolateral striatum (VLS), a subregion of the ventral striatum (VS), possesses distinct neuronal Ca2+ activities and functions in reward-oriented behavior, compared with the ventromedial striatum (VMS) based on the anatomical feature. We hypothesized that the VLS exhibits unique neuronal activity and function in nociceptive processing, a part of aversive processing. Using fiber photometry to monitor the neuronal Ca2+ activities, we demonstrated that acute noxious mechanical stimuli like tail-pinch increased the Ca2+ activity of dopamine D2 receptor-expressing medium spiny neurons (D2-MSNs) in the VLS in correlation with the stimulus intensities in mice, whereas mechanical stimuli increased the VMS D2-MSN activity independent of the stimulus intensities. Likewise, thermal stimuli decreased the VLS and VMS D2-MSN Ca2+ activities during nociceptive behaviors in the hot plate test. Furthermore, the VLS D2-MSNs increased their Ca2+ activity accompanied by formalin-induced nociceptive behaviors in mice, whereas the VMS D2-MSNs decreased it. The optogenetic inhibition of VLS D2-MSN activity increased the formalin-induced pain-related behavior in mice, thus suggesting the inhibitory effect of VLS D2-MSN activity on chemical nociceptive behavior, in contrast to previous reports that the VMS D2-MSNs could not involve the behavior. Therefore, the VLS D2-MSNs exhibited region-specific roles in nociception.
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Nociceptividade , Estriado Ventral , Camundongos , Animais , Neurônios Espinhosos Médios , Receptores de Dopamina D2/metabolismo , Corpo Estriado/metabolismo , Neurônios/fisiologia , Receptores de Dopamina D1/metabolismo , Camundongos Transgênicos , Camundongos Endogâmicos C57BLRESUMO
Adverse experience, such as social isolation, during adolescence is one of the major causes of neuropsychiatric disorders that extend from adolescence into adulthood, such as substance addiction, obsessive-compulsive disorder, and eating disorders leading to obesity. A common behavioral feature of these neuropsychiatric disorders is a shift in the balance of decision-making strategy from goal-directed action to habitual response. This study has verified that adolescent social isolation directly shifts the balance of decision-making strategy from goal-directed action to habitual response, and that it cannot be reversed by simple regrouping. This study has further revealed that adolescent social isolation induces a suppression in the excitatory neurotransmission onto the direct-pathway medium spiny neurons of the dorsomedial striatum (DMS), and that chemogenetically compensating this suppression effect shifts the balance of decision-making strategy from habitual response back to goal-directed action. These findings suggest that the plasticity in the DMS causes the shift in the balance of decision-making strategy, which would potentially help to develop a general therapy to treat the various neuropsychiatric disorders caused by adolescent social isolation. Such a study is especially necessary under the circumstances that social distancing and lockdown have caused during times of world-wide, society-wide pandemic.
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Corpo Estriado , Objetivos , Adolescente , Humanos , Corpo Estriado/fisiologia , Motivação , Transmissão Sináptica/fisiologia , Isolamento SocialRESUMO
BACKGROUND: Hydrocephalus is characterized by abnormal accumulation of cerebrospinal fluid in the cerebral ventricles and causes motor impairments. The mechanisms underlying the motor changes remain elusive. Enlargement of ventricles compresses the striatum of the basal ganglia, a group of nuclei involved in the subcortical motor circuit. Here, we used a kaolin-injection juvenile rat model to explore the effects of acute and chronic hydrocephalus, 1 and 5 weeks post-treatment, respectively on the three major neurotransmission pathways (glutamatergic, dopaminergic and cholinergic) in the striatum. METHODS: Rats were evaluated for motor impairments. Expressions of presynaptic and postsynaptic protein markers related to the glutamatergic, dopaminergic, and cholinergic connections in the striatum were evaluated. Combined intracellular dye injection and substance P immunohistochemistry were used to distinguish between direct and indirect pathway striatal medium spiny neurons (d and i-MSNs) for the analysis of their dendritic spine density changes. RESULTS: Hydrocephalic rats showed compromised open-field gait behavior. However, male but not female rats displayed stereotypic movements and compromised rotarod performance. Morphologically, the increase in lateral ventricle sizes was greater in the chronic than acute hydrocephalus conditions. Biochemically, hydrocephalic rats had significantly decreased striatal levels of synaptophysin, vesicular glutamate transporter 1, and glutamatergic postsynaptic density protein 95, suggesting a reduction of corticostriatal excitation. The expression of GluR2/3 was also reduced suggesting glutamate receptor compositional changes. The densities of dendritic spines, morphological correlates of excitatory synaptic foci, on both d and i-MSNs were also reduced. Hydrocephalus altered type 1 (DR1) and 2 (DR2) dopamine receptor expressions without affecting tyrosine hydroxylase level. DR1 was decreased in acute and chronic hydrocephalus, while DR2 only started to decrease later during chronic hydrocephalus. Since dopamine excites d-MSNs through DR1 and inhibits i-MSNs via DR2, our findings suggest that hydrocephalus downregulated the direct basal ganglia neural pathway persistently and disinhibited the indirect pathway late during chronic hydrocephalus. Hydrocephalus also persistently reduced the striatal choline acetyltransferase level, suggesting a reduction of cholinergic modulation. CONCLUSIONS: Hydrocephalus altered striatal glutamatergic, dopaminergic, and cholinergic neurotransmission pathways and tipped the balance between the direct and indirect basal ganglia circuits, which could have contributed to the motor impairments in hydrocephalus.
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Dopamina , Hidrocefalia , Ratos , Masculino , Animais , Dopamina/fisiologia , Caulim/toxicidade , Transmissão Sináptica , Hidrocefalia/induzido quimicamente , ColinérgicosRESUMO
Despite combination antiretroviral therapy, HIV-associated neurocognitive disorders (HAND) occur in ~50% of people living with HIV (PLWH), which are associated with dysfunction of the corticostriatal pathway. The mechanism by which HIV alters the neuronal activity in the striatum is unknown. The goal of this study is to reveal the dysfunction of striatal neurons in the context of neuroHIV during aging. Using patch-clamping electrophysiology, we evaluated the functional activity of medium spiny neurons (MSNs), including firing, Ca2+ spikes mediated by voltage-gated Ca2+ channels (VGCCs), and K+ channel-mediated membrane excitability, in brain slices containing the dorsal striatum (a.k.a. the caudate-putamen) from 12-month-old (12mo) HIV-1 transgenic (HIV-1 Tg) rats. We also assessed the protein expression of voltage-gated Cav1.2/Cav1.3 L-type Ca2+ channels (L-channels), NMDA receptors (NMDAR, NR2B subunit), and GABAA receptors (GABAARs, ß2,3 subunit) in the striatum. We found that MSNs had significantly increased firing in 12mo HIV-1 Tg rats compared to age-matched non-Tg control rats. Unexpectedly, Ca2+ spikes were significantly reduced, while Kv channel activity was increased, in MSNs of HIV-1 Tg rats compared to non-Tg ones. The reduced Ca2+ spikes were associated with an abnormally increased expression of a shorter, less functional Cav1.2 L-channel form, while there was no significant change in the expression of NR2Bs or GABAARs. Collectively, the present study initially reveals neuroHIV-induced dysfunction of striatal MSNs in 12mo-old (middle) rats, which is uncoupled from VGCC upregulation and reduced Kv activity (that we previously identified in younger HIV-1 Tg rats). Notably, such striatal dysfunction is also associated with HIV-induced hyperactivity/neurotoxicity of glutamatergic pyramidal neurons in the medial prefrontal cortex (mPFC) that send excitatory input to the striatum (demonstrated in our previous studies). Whether such MSN dysfunction is mediated by alterations in the functional activity instead of the expression of NR2b/GABAAR (or other subtypes) requires further investigation.
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The ability to use environmental cues to flexibly guide responses is crucial for adaptive behavior and is thought to be controlled within a series of cortico-basal ganglia-thalamo-cortical loops. Previous evidence has indicated that different prefrontal cortical regions control dissociable aspects of behavioral flexibility, with the medial prefrontal cortex (mPFC) necessary for the ability to shift attention to a novel strategy (set-shifting) and the orbitofrontal cortex (OFC) necessary for shifting attention between learned stimulus-outcome associations (reversal learning). The nucleus accumbens (NAc) is a major downstream target of both the mPFC and the OFC; however, its role in controlling reversal learning and set-shifting abilities is still unclear. Here we investigated the contribution of the two major NAc neuronal populations, medium spiny neurons expressing either dopamine D1 or D2 receptors (D1-/D2-MSNs), in guiding reversal learning and set-shifting in an attentional set-shifting task (ASST). Persistent inhibition of neurotransmitter release from NAc D2-MSNs, but not D1-MSNs, resulted in an impaired ability for reversal learning, but not set-shifting in male mice. These findings suggest that NAc D2-MSNs play a critical role in suppressing responding toward specific learned cues that are now associated with unfavorable outcomes (i.e., in reversal stages), but not in the suppression of more general learned strategies (i.e., in set-shifting). This study provides further evidence for the anatomical separation of reversal learning and set-shifting abilities within cortico-basal ganglia-thalamo-cortical loops.