Neurons In Striatum Research Articles

Direct Pathway Neurons in the Mouse Ventral Striatum Are Active During Goal-Directed Action but Not Reward Consumption During Operant Conditioning

Background/Objectives: Learning is classically modeled to consist of an acquisition period followed by a mastery period when the skill no longer requires conscious control and becomes automatic. Dopamine neurons projecting to the ventral striatum (VS) produce a teaching signal that shifts from responding to rewarding or aversive events to anticipating cues, thus facilitating learning. However, the role of the dopamine-receptive neurons in the ventral striatum, particularly in encoding decision-making processes, remains less understood. Methods: Here, we introduce an operant conditioning paradigm using open-source microcontrollers to train mice in three sequential learning phases. Phase I employs classical conditioning, associating a 5 s sound cue (CS) with a sucrose–water reward. In Phase II, the CS is replaced by a lever press as the requirement for reward delivery, marking an operant conditioning stage. Phase III combines these elements, requiring mice to press the lever during the CS to obtain the reward. We recorded calcium signals from direct pathway spiny projection neurons (dSPNs) in the VS throughout the three phases of training. Results: We find that dSPNs are specifically engaged when the mouse makes a decision to perform a reward-seeking action in response to a CS but are largely inactive during actions taken outside the CS. Conclusions: These findings suggest that direct pathway neurons in the VS contribute to decision-making in learned action–outcome associations, indicating a specialized role in initiating operant behaviors.

Dietary regulation of silent synapses in the dorsolateral striatum

Obesity and drugs of abuse share overlapping neural circuits and behaviors. Silent synapses are transient synapses that are important for remodeling brain circuits. They are prevalent during early development but largely disappear by adulthood. Drugs of abuse increase silent synapses during adulthood and may facilitate reorganizing brain circuits around drug-related experience, facilitating addiction and contributing to relapse during treatment and abstinence. Whether obesity causes alterations in the expression of silent synapses in a manner similar to drugs of abuse has not been examined. Using a dietary-induced obesity paradigm, mice that chronically consumed high fat diet (HFD) exhibited increased silent synapses in both direct and indirect pathway medium spiny neurons in the dorsolateral striatum. Both the time of onset of increased silent synapses and their normalization upon discontinuation of HFD occurs on an extended time scale compared to drugs of abuse. These data demonstrate that chronic consumption of HFD, like drugs of abuse, can alter mechanisms of circuit plasticity likely facilitating neural reorganization analogous to drugs of abuse.

DIETARY REGULATION OF SILENT SYNAPSES IN THE DORSOLATERAL STRIATUM.

Obesity and drugs of abuse share overlapping neural circuits and behaviors. Silent synapses are transient synapses that are important for remodeling brain circuits. They are prevalent during early development but largely disappear by adulthood. Drugs of abuse increase silent synapses during adulthood and may facilitate reorganizing brain circuits around drug-related experience, facilitating addiction and contributing to relapse during treatment and abstinence. Whether obesity causes alterations in the expression of silent synapses in a manner similar to drugs of abuse has not been examined. Using a dietary-induced obesity paradigm, mice that chronically consumed high fat diet (HFD) exhibited increased silent synapses in both direct and indirect pathway medium spiny neurons in the dorsolateral striatum. Both the time of onset of increased silent synapses and their normalization upon discontinuation of HFD occurs on an extended time scale compared to drugs of abuse. These data demonstrate that chronic consumption of HFD, like drugs of abuse, can alter mechanisms of circuit plasticity likely facilitating neural reorganization analogous to drugs of abuse.

Optogenetic stimulation of dorsal striatum bidirectionally controls seizures.

Engagement of the striatum (caudate/putamen) and other basal ganglia nuclei during seizures was first observed over 75 years ago. Basal ganglia output nuclei, and the substantia nigra pars reticulata, in particular, have well-established anti-seizure effects across a large array of experimental models. However, striatal control of seizures is understudied. To address this gap, we used optogenetic approaches to activate and inactivate neurons in the dorsal striatum of Sprague-Dawley rats submitted to the gamma-butyrolactone (GBL) model of absence epilepsy, amygdala kindling model of temporal lobe epilepsy, and pilocarpine-induced Status Epilepticus (SE). All tests were performed on a within-subject basis. Animals were tested in two different light frequencies (5 Hz and 100 Hz). Open-loop (continuous light delivery) optogenetic activation of the dorsal striatal neurons robustly suppressed seizures in all models. On the other hand, optogenetic silencing of the dorsal striatal neurons increased absence seizure expression and facilitated SE onset but had no effect on kindled limbic seizures. In the GBL model, we also verified if the closed- loop strategy (light delivery in response to seizure detection) would be enough to induce antiseizure effects. On-demand light delivery in ChR2-expressing animals reduced SWD duration, while the same approach in ArchT-expressing animals increased SWD duration. These results demonstrated previously unrecognized anti-absence effects associated with striatal continuous and on-demand neuromodulation. Together, these findings document a robust, bidirectional role of the dorsal striatum in the control of seizure generation and propagation in a variety of seizure models, including focal seizure onset and generalized seizures.

Rewarding properties of L-Dopa in experimental parkinsonism are mediated by sensitized dopamine D1 receptors in the dorsal striatum.

Treatment of Parkinson's disease (PD) is based on the use of dopaminergic drugs, such as L-Dopa and dopamine receptor agonists. These substances counteract motor symptoms, but their administration is accompanied by motor and non-motor complications. Among these latter conditions a neurobehavioral disorder similar to drug abuse, known as dopamine dysregulation syndrome (DDS), is attracting increasing interest because of its profound negative impact on the patients' quality of life. Here we replicate DDS in a PD mouse model based on a bilateral injection of 6-hydroxydopamine (6-OHDA) into the dorsal striatum. Administration of L-Dopa induced locomotor sensitization and conditioned place preference in 6-OHDA lesion, but not in control mice, indicative of the acquisition of addictive-like properties following nigrostriatal dopamine depletion. These behavioral effects were accompanied by abnormal dopamine D1 receptor (D1R) signaling in the medium spiny neurons of the dorsal striatum, leading to hyperactivation of multiple signaling cascades and increased expression of ΔFosB, a stable transcription factor involved in addictive behavior. Systemic administration of the D1R antagonist, SCH23390, abolished these effects and the development of place preference, thereby counteracting the psychostimulant-like effect of L-Dopa. The rewarding properties of L-Dopa were also prevented by chemogenetic inactivation of D1R-expressing neurons in the dorsal striatum. Our results indicate the association between abnormal D1R-mediated transmission and DDS in PD and identify potential approaches for the treatment of this disorder.

Transitions in dynamical regime and neural mode underlie perceptual decision-making.

Perceptual decision-making is the process by which an animal uses sensory stimuli to choose an action or mental proposition. This process is thought to be mediated by neurons organized as attractor networks 1,2 . However, whether attractor dynamics underlie decision behavior and the complex neuronal responses remains unclear. Here we use an unsupervised, deep learning-based method to discover decision-related dynamics from the simultaneous activity of neurons in frontal cortex and striatum of rats while they accumulate pulsatile auditory evidence. We found that trajectories evolved along two sequential regimes, the first dominated by sensory inputs, and the second dominated by the autonomous dynamics, with flow in a direction (i.e., "neural mode") largely orthogonal to that in the first regime. We propose that the second regime corresponds to decision commitment. We developed a simplified model that approximates the coupled transition in dynamics and neural mode and allows precise inference, from each trial's neural activity, of a putative internal decision commitment time in that trial. The simplified model captures diverse and complex single-neuron temporal profiles, such as ramping and stepping 3-5 . It also captures trial-averaged curved trajectories 6-8 , and reveals distinctions between brain regions. The putative neurally-inferred commitment times ("nTc") occurred at times broadly distributed across trials, and not time-locked to stimulus onset, offset, or response onset. Nevertheless, when trials were aligned to nTc, behavioral analysis showed that, as predicted by a decision commitment time, sensory evidence before nTc affected the subjects' decision, but evidence after nTc did not. Our results show that the formation of a perceptual choice involves a rapid, coordinated transition in both the dynamical regime and the neural mode of the decision process, and suggest the moment of commitment to be a useful entry point for dissecting mechanisms underlying rapid changes in internal state.

Sniffing can be initiated by dopamine's actions on ventral striatum neurons.

Sniffing is a motivated behavior displayed by nearly all terrestrial vertebrates. While sniffing is associated with acquiring and processing odors, sniffing is also intertwined with affective and motivated states. The neuromodulatory systems which influence the display of sniffing are unclear. Here, we report that dopamine release into the ventral striatum is coupled with bouts of sniffing and that stimulation of dopaminergic terminals in these regions drives increases in respiratory rate to initiate sniffing whereas inhibition of these terminals reduces respiratory rate. Both the firing of individual neurons and the activity of post-synaptic D1 and D2 receptor-expressing neurons in the ventral striatum are also coupled with sniffing and local antagonism of D1 and D2 receptors squelches sniffing. Together, these results support a model whereby sniffing can be initiated by dopamine's actions upon ventral striatum neurons. The nature of sniffing being integral to both olfaction and motivated behaviors implicates this circuit in a wide array of functions.

Loss of primary cilia and dopaminergic neuroprotection in pathogenic LRRK2-driven and idiopathic Parkinson’s disease

Activating leucine-rich repeat kinase 2 (LRRK2) mutations cause Parkinson's and phosphorylation of Rab10 by pathogenic LRRK2 blocks primary ciliogenesis in cultured cells. In the mouse brain, LRRK2 blockade of primary cilia is highly cell type specific: For example, cholinergic interneurons and astrocytes but not medium spiny neurons of the dorsal striatum lose primary cilia in LRRK2-pathway mutant mice. We show here that the cell type specificity of LRRK2-mediated cilia loss is also seen in human postmortem striatum from patients with LRRK2 pathway mutations and idiopathic Parkinson's. Single nucleus RNA sequencing shows that cilia loss in mouse cholinergic interneurons is accompanied by decreased glial-derived neurotrophic factor transcription, decreasing neuroprotection for dopamine neurons. Nevertheless, LRRK2 expression differences cannot explain the unique vulnerability of cholinergic neurons to LRRK2 kinase as much higher LRRK2 expression is seen in medium spiny neurons that have normal cilia. In parallel with decreased striatal dopaminergic neurite density, LRRK2 G2019S neurons show increased autism-linked CNTN5 adhesion protein expression; glial cells show significant loss of ferritin heavy chain. These data strongly suggest that loss of cilia in specific striatal cell types decreases neuroprotection for dopamine neurons in mice and human Parkinson's.

Anterior cingulate cortex lesions impair multiple facets of task engagement not mediated by dorsomedial striatum neuron firing.

The anterior cingulate cortex (ACC) has been implicated across multiple highly specialized cognitive functions-including task engagement, motivation, error detection, attention allocation, value processing, and action selection. Here, we ask if ACC lesions disrupt task performance and firing in dorsomedial striatum (DMS) during the performance of a reward-guided decision-making task that engages many of these cognitive functions. We found that ACC lesions impacted several facets of task performance-including decreasing the initiation and completion of trials, slowing reaction times, and resulting in suboptimal and inaccurate action selection. Reductions in movement times towards the end of behavioral sessions further suggested attenuations in motivation, which paralleled reductions in directional action selection signals in the DMS that were observed later in recording sessions. Surprisingly, however, beyond altered action signals late in sessions-neural correlates in the DMS were largely unaffected, even though behavior was disrupted at multiple levels. We conclude that ACC lesions result in overall deficits in task engagement that impact multiple facets of task performance during our reward-guided decision-making task, which-beyond impacting motivated action signals-arise from dysregulated attentional signals in the ACC and are mediated via downstream targets other than DMS.

Moxibustion improves motor function by down-regulating SNX5 and inhibiting ferroptosis in neurons of corpus striatum in mice with Parkinson's disease.

To explore the effect of moxibustion on the expression of sorting nexin 5 (SNX5), glutathione peroxidase (GPX4) and ferritin heavy chain (FTH1) in the corpus striatum in mice with Parkinson's disease (PD), so as to explore its mechanisms underlying improvement of PD by ameliorating ferroptosis in the substantia nigra striatum. C57BL/6J mice were randomly divided into normal, sham operation, model, and moxibustion groups, with 10 mice in each group. The PD model was established by unilateral injection of 6-hydroxydopamine (3.5 μL) into the right medial forebrain bundle (AP=-1.2 mm, ML=-1.3 mm, DV=-4.75 mm). The mice in the moxibustion group received moxibustion at "Baihui"(GV20) and "Sishencong"(EX-HN1) for 20 min each time, once a day, 6 times a week for 4 weeks. After the intervention, mice received apomorphine rotation behavior detection and pole climbing test. The expression of tyrosine hydroxylase (TH) in the substantia nigra was detected by immunofluorescence, the contents of Fe2+, malondialdehyde (MDA), the ratio of glutathione/oxidized glutathione (GSH/GSSG) in the corpus striatum were detected by using photocolorimetric method, and the expression levels of SNX5 (endocytosomal protein), GPX4 (one of the key targets for inhibiting ferroptosis) and FTH1 proteins and mRNAs in the corpus striatum were detected by Western blot and qPCR, respectively. Behavior tests showed that the pole climbing time and number of body rotation were significantly increased in the model group relevant to the sham operation group (P<0.01), and strikingly decreased in the moxibustion group relevant to the model group (P<0.01). The immunofluorescence intensity of TH in the substantia nigra, the ratio of GSH/GSSG, and the expression levels of GPX4 and FTH1 mRNAs and proteins in the corpus striatum were markedly decreased (P<0.01, P<0.05), while the contents of Fe2+ and MDA and the expression levels of SNX5 mRNA and protein in the corpus striatum significantly increased in the model group relevant to the sham operation group (P<0.01, P<0.05). Compared with the model group, the decreased immunofluorescence intensity of TH, GSH/GSSH, and the expression levels of GPX4 and FTH1 mRNAs and proteins, and the increased contents of Fe2+ and MDA and the expression levels of SNX5 mRNA and protein were reversed in the moxibustion group relevant to the model group (P<0.01, P<0.05). Moxibustion may improve motor dysfunction in PD mice, which may be related to its effects in down-regulating the expression of SNX5, promoting the synthesis of GSH, decreasing the contents of Fe2+ and MDA, up-regulating the ratio of GSH/GSSG and the expression of GPX4 and FTH1 mRNAs and proteins in the corpus striatum, and inhibiting the occurrence of ferroptosis.

Efficient Dlx2-mediated astrocyte-to-neuron conversion and inhibition of neuroinflammation by NeuroD1.

In vivo astrocyte-to-neuron (AtN) conversion induced by overexpression of neural transcriptional factors has great potential for neural regeneration and repair. Here, we demonstrate that a single neural transcriptional factor, Dlx2, converts mouse striatal astrocytes into neurons in a dose-dependent manner. Lineage-tracing studies in Aldh1l1-CreERT2 mice confirm that Dlx2 can convert striatal astrocytes into DARPP32+ and Ctip2+ medium spiny neurons (MSNs). Time-course studies reveal a gradual conversion from astrocytes to neurons in 1 month, with a distinct intermediate state in between astrocytes and neurons. Interestingly, when Dlx2-infected astrocytes start to lose astrocytic markers, the other local astrocytes proliferate to maintain astrocytic levels in the converted areas. Unexpectedly, although Dlx2 efficiently reprograms astrocytes into neurons in the gray matter striatum, it also induces partial reprogramming of astrocytes in the white matter corpus callosum. Such partial reprogramming of white matter astrocytes is associated with neuroinflammation, which can be suppressed by the addition of NeuroD1. Our results highlight the importance of investigating AtN conversion in both the gray matter and white matter to thoroughly evaluate therapeutic potentials. This study also unveils the critical role of anti-inflammation by NeuroD1 during AtN conversion.

Bidirectional modulation of negative emotional states by parallel genetically-distinct basolateral amygdala pathways to ventral striatum subregions.

Distinct basolateral amygdala (BLA) cell populations influence emotional responses in manners thought important for anxiety and anxiety disorders. The BLA contains numerous cell types which can broadcast information into structures that may elicit changes in emotional states and behaviors. BLA excitatory neurons can be divided into two main classes, one of which expresses Ppp1r1b (encoding protein phosphatase 1 regulatory inhibitor subunit 1B) which is downstream of the genes encoding the D1 and D2 dopamine receptors (drd1 and drd2 respectively). The role of drd1+ or drd2+ BLA neurons in learned and unlearned emotional responses is unknown. Here, we identified that the drd1+ and drd2+ BLA neuron populations form two parallel pathways for communication with the ventral striatum. These neurons arise from the basal nucleus of the BLA, innervate the entire space of the ventral striatum, and are capable of exciting ventral striatum neurons. Further, through three separate behavioral assays, we found that the drd1+ and drd2+ parallel pathways bidirectionally influence both learned and unlearned emotional states when they are activated or suppressed, and do so depending upon where they synapse in the ventral striatum - with unique contributions of drd1+ and drd2+ circuitry on negative emotional states. Overall, these results contribute to a model whereby parallel, genetically-distinct BLA to ventral striatum circuits inform emotional states in a projection-specific manner.

Alcohol consumption does not impact delta and kappa opioid receptor-mediated synaptic depression in dorsolateral striatum of adult male mice

Many drugs of abuse, including alcohol, disrupt long-term synaptic depression (LTD) at dorsal striatal glutamate synapses. This disruption is common to many forms of LTD that are mediated by G protein coupled receptors (GPCRs) that signal through the inhibitory Gi/o class of G proteins. A loss of LTD is thought to mediate behavioral changes associated with the development of substance use disorders. We have previously shown in multiple studies that LTD mediated by the Gi/o-coupled mu opioid receptor is disrupted by in vivo opioid and alcohol exposure in adolescent and adult mice. One of our previous studies suggested that LTD mediated by delta and kappa opioid receptors was resistant to the LTD-disrupting properties of in vivo opioid exposure. We hypothesized that delta and kappa opioid receptor-mediated LTD would be exceptions to the generalizable observation that forms of dorsal striatal Gi/o-coupled receptor LTD are disrupted by drugs of abuse. Specifically, we predicted that these forms of LTD would be resistant to the deleterious effects of alcohol consumption, just as they were resistant to opioid exposure. Indeed, in adult male mice that drank alcohol for 3 weeks, delta and kappa opioid receptor-mediated LTD at glutamatergic inputs to direct pathway and indirect pathway medium spiny neurons in the dorsolateral striatum was unaffected by alcohol. These data demonstrate that alcohol effects on GPCR-mediated LTD are not generalizable across all types of Gi/o-coupled GPCRs.

Disruption of the mitochondrial network in a mouse model of Huntington's disease visualized by in-tissue multiscale 3D electron microscopy

Huntington’s disease (HD) is an inherited neurodegenerative disorder caused by an expanded CAG repeat in the coding sequence of huntingtin protein. Initially, it predominantly affects medium-sized spiny neurons (MSSNs) of the corpus striatum. No effective treatment is still available, thus urging the identification of potential therapeutic targets. While evidence of mitochondrial structural alterations in HD exists, previous studies mainly employed 2D approaches and were performed outside the strictly native brain context. In this study, we adopted a novel multiscale approach to conduct a comprehensive 3D in situ structural analysis of mitochondrial disturbances in a mouse model of HD. We investigated MSSNs within brain tissue under optimal structural conditions utilizing state-of-the-art 3D imaging technologies, specifically FIB/SEM for the complete imaging of neuronal somas and Electron Tomography for detailed morphological examination, and image processing-based quantitative analysis. Our findings suggest a disruption of the mitochondrial network towards fragmentation in HD. The network of interlaced, slim and long mitochondria observed in healthy conditions transforms into isolated, swollen and short entities, with internal cristae disorganization, cavities and abnormally large matrix granules.

Comparison of unitary synaptic currents generated by indirect and direct pathway neurons of the mouse striatum.

Two subtypes of striatal spiny projection neurons, iSPNs and dSPNs, whose axons form the "indirect" and "direct" pathways of the basal ganglia, respectively, both make synaptic connections in the external globus pallidus (GPe) but are usually found to have different effects on behavior. Activation of the terminal fields of iSPNs or dSPNs generated compound currents in almost all GPe neurons. To determine whether iSPNs and dSPNs have the same or different effects on pallidal neurons, we studied the unitary synaptic currents generated in GPe neurons by action potentials in single striatal neurons. We used optogenetic excitation to elicit repetitive firing in a small number of nearby SPNs, producing sparse barrages of inhibitory postsynaptic currents (IPSCs) in GPe neurons. From these barrages, we isolated sequences of IPSCs with similar time courses and amplitudes, which presumably arose from the same SPN. There was no difference between the amplitudes of unitary IPSCs generated by the indirect and direct pathways. Most unitary IPSCs were small, but a subset from each pathway were much larger. To determine the effects of these unitary synaptic currents on the action potential firing of GPe neurons, we drove SPNs to fire as before and recorded the membrane potential of GPe neurons. Large unitary potentials from iSPNs and dSPNs perturbed the spike timing of GPe neurons in a similar way. Most SPN-GPe neuron pairs are weakly connected, but a subset of pairs in both pathways are strongly connected.NEW & NOTEWORTHY This is the first study to record the synaptic currents generated by single identified direct or indirect pathway striatal neurons on single pallidal neurons. Each GPe neuron receives synaptic inputs from both pathways. Most striatal neurons generate small synaptic currents that become influential when occurring together, but a few are powerful enough to be individually influential.

Synthesis of Novel Plant-Derived Encapsulated Radiolabeled Compounds for the Diagnosis of Parkinson's Disease and the Evaluation of Biological Effects with In Vitro/In Vivo Methods.

Parkinson's disease (PD) is a neurodegenerative disorder that affects millions of individuals globally. It is characterized by the loss of dopaminergic neurons in Substantia Nigra pars compacta (SNc) and striatum. Neuroimaging techniques such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), and magnetic resonance imaging (MRI) help diagnosing PD. In this study, the focus was on developing technetium-99m ([99mTc]Tc) radiolabeled drug delivery systems using plant-derived compounds for the diagnosis of PD. Madecassoside (MA), a plant-derived compound, was conjugated with Levodopa (L-DOPA) to form MA-L-DOPA, which was then encapsulated using Poly Lactic-co-Glycolic Acid (PLGA) to create MA-PLGA and MA-L-DOPA-PLGA nanocapsules. Extensive structural analysis was performed using various methods such as Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), liquid chromatography-mass spectrometry (LC-MS), thin layer chromatography (TLC), high performance liquid chromatography (HPLC), dynamic light scattering (DLS), and scanning electron microscopy (SEM) to characterize the synthesized products. Radiochemical yields of radiolabeled compounds were determined using thin layer radio chromatography (TLRC) and high performance liquid radio chromatography (HPLRC) methods. In vitro cell culture studies were conducted on human neuroblastoma (SH-SY5Y) and rat pheochromocytoma (PC-12) cell lines to assess the incorporation of [99mTc]Tc radiolabeled compounds ([99mTc]Tc-MA, [99mTc]Tc-MA-L-DOPA, [99mTc]Tc-MA-PLGA and [99mTc]Tc-MA-L-DOPA-PLGA) and the cytotoxicity of inactive compounds (MA and MA-L-DOPA compounds and encapsulated compounds (MA-PLGA and MA-L-DOPA-PLGA). Additionally, the biodistribution studies were carried out on healthy male Sprague-Dawley rats and a Parkinson's disease experimental model to evaluate the compounds' bioactivity using the radiolabeled compounds. The radiochemical yields of all radiolabeled compounds except [99mTc]Tc-L-DOPA-PLGA were above 95% and had stability over 6h. The cytotoxic effects of all substances on SH-SY5Y and PC-12 cells increase with increasing concentration values. The uptake values of PLGA-encapsulated compounds are statistically significant in SH-SY5Y and PC-12 cells. The biodistribution studies showed that [99mTc]Tc-MA is predominantly retained in specific organs and brain regions, with notable uptake in the prostate, muscle, and midbrain. PLGA-encapsulation led to higher uptake in certain organs, suggesting its biodegradable nature may enhance tissue retention, and surface modifications might further optimize brain penetration. Overall, the results indicate that radiolabeled plant-derived encapsulated drug delivery systems with [99mTc]Tc hold potential as diagnostic agents for PD symptoms. This study contributes to the advancement of drug delivery agents in the field of brain research.

Hyperactive mTORC1 in striatum dysregulates dopamine receptor expression and odor preference behavior.

Mechanistic target of rapamycin (mTOR) plays an important role in brain development and synaptic plasticity. Dysregulation of the mTOR pathway is observed in various human central nervous system diseases, including tuberous sclerosis complex, autism spectrum disorder (ASD), and neurodegenerative diseases, including Parkinson's disease and Huntington's disease. Numerous studies focused on the effects of hyperactivation of mTOR on cortical excitatory neurons, while only a few studies focused on inhibitory neurons. Here we generated transgenic mice in which mTORC1 signaling is hyperactivated in inhibitory neurons in the striatum, while cortical neurons left unaffected. The hyperactivation of mTORC1 signaling increased GABAergic inhibitory neurons in the striatum. The transgenic mice exhibited the upregulation of dopamine receptor D1 and the downregulation of dopamine receptor D2 in medium spiny neurons in the ventral striatum. Finally, the transgenic mice demonstrated impaired motor learning and dysregulated olfactory preference behavior, though the basic function of olfaction was preserved. These findings reveal that the mTORC1 signaling pathway plays an essential role in the development and function of the striatal inhibitory neurons and suggest the critical involvement of the mTORC1 pathway in the locomotor abnormalities in neurodegenerative diseases and the sensory defects in ASD.

Chemogenetic Silencing of Neonatal Spontaneous Activity of Projection Neurons in the Dorsal Striatum of Mice.

Neuroscience incorporates manipulating neuronal circuitry to enhance the understanding of intricate brain functions. An effective strategy to attain this objective entails utilizing viral vectors to induce varied gene expression by delivering transgenes into brain cells. Here, we combine the use of transgenic mice, neonatal transduction with adeno-associated viral constructs harboring inhibitory designer receptor exclusively activated by designer drug (DREADD) gene, and the DREADD agonist clozapine N-oxide (CNO). In this way, a chemogenetic approach is employed to suppress neuronal activity in the region of interest during a critical developmental window, with subsequent investigation into its effects on the neuronal circuitry in adulthood. Key features • Comprehensive protocol for newborn viral transduction in the dorsal striatum of mice • Uses a viral construct encoding inhibitory DREADD under the control of Cre recombinase to attenuate the activity of specific cell types in the brain.

Astrocyte Ca2+ in the dorsal striatum suppresses neuronal activity to oppose cue-induced reinstatement of cocaine seeking.

Recent literature supports a prominent role for astrocytes in regulation of drug-seeking behaviors. The dorsal striatum, specifically, is known to play a role in reward processing with neuronal activity that can be influenced by astrocyte Ca2+. However, the manner in which Ca2+ in dorsal striatum astrocytes impacts neuronal signaling after exposure to self-administered cocaine remains unclear. We addressed this question following over-expression of the Ca2+ extrusion pump, hPMCA2w/b, in dorsal striatum astrocytes and the Ca2+ indicator, GCaMP6f, in dorsal striatum neurons of rats that were trained to self-administer cocaine. Following extinction of cocaine-seeking behavior, the rats over-expressing hMPCA2w/b showed a significant increase in cue-induced reinstatement of cocaine seeking. Suppression of astrocyte Ca2+ increased the amplitude of neuronal Ca2+ transients in brain slices, but only after cocaine self-administration. This was accompanied by decreased duration of neuronal Ca2+ events in the cocaine group and no changes in Ca2+ event frequency. Acute administration of cocaine to brain slices decreased amplitude of neuronal Ca2+ in both the control and cocaine self-administration groups regardless of hPMCA2w/b expression. These results indicated that astrocyte Ca2+ control over neuronal Ca2+ transients was enhanced by cocaine self-administration experience, although sensitivity to acutely applied cocaine remained comparable across all groups. To explore this further, we found that neither the hMPCA2w/b expression nor the cocaine self-administration experience altered regulation of neuronal Ca2+ events by NPS-2143, a Ca2+ sensing receptor (CaSR) antagonist, suggesting that plasticity of neuronal signaling after hPMCA2w/b over-expression was unlikely to result from elevated extracellular Ca2+. We conclude that astrocyte Ca2+ in the dorsal striatum impacts neurons via cell-intrinsic mechanisms (e.g., gliotransmission, metabolic coupling, etc.) and impacts long-term neuronal plasticity after cocaine self-administration differently from neuronal response to acute cocaine. Overall, astrocyte Ca2+ influences neuronal output in the dorsal striatum to promote resistance to cue-induced reinstatement of cocaine seeking.

Short-term stimulations of the entopeduncular nucleus induce cerebellar changes of c-Fos expression in an animal model of paroxysmal dystonia

Deep brain stimulation (DBS) of the globus pallidus internus (entopeduncular nucleus, EPN, in rodents) is important for the treatment of drug-refractory dystonia. The pathophysiology of this movement disorder and the mechanisms of DBS are largely unknown. Insights into the mechanisms of DBS in animal models of dystonia can be helpful for optimization of DBS and add-on therapeutics. We recently found that short-term EPN-DBS with 130 Hz (50 µA, 60 µs) for 3 h improved dystonia in dtsz hamsters and reduced spontaneous excitatory cortico-striatal activity in brain slices of this model, indicating fast effects on synaptic plasticity. Therefore, in the present study, we examined if these effects are related to changes of c-Fos, a marker of neuronal activity, in brains derived from dtsz hamsters after these short-term DBS or sham stimulations. After DBS vs. sham, c-Fos intensity was increased around the electrode, but the number of c-Fos+ cells was not altered within the whole EPN and projection areas (habenula, thalamus). DBS did not induce changes in striatal and cortical c-Fos+ cells as GABAergic (GAD67+ and parvalbumin-reactive) neurons in motor cortex and striatum. Unexpectedly, c-Fos+ cells were decreased in deep cerebellar nuclei (DCN) after DBS, suggesting that cerebellar changes may be involved in antidystonic effects already during short-term DBS. However, the present results do not exclude functional changes within the basal ganglia–thalamo-cortical network, which will be further investigated by long-term EPN stimulations. The present study indicates that the cerebellum deserves attention in ongoing examinations on the mechanisms of DBS in dystonia.