The dual role of striatal interneurons:circuit modulation and trophic support for the basal ganglia

Striatal interneurons play a key role in modulating striatal-dependent behaviors,including motor activity and reward and emotional processing.Interneurons not only provide modulation to the basal ganglia circuitry under homeostasis but are also involved in changes to plasticity and adaptation during disease conditions such as Parkinson's or Huntington's disease.This review aims to summarize recent findings regarding the role of striatal cholinergic and GABAergic interneurons in providing circuit modulation to the basal ganglia in both homeostatic and disease conditions.In addition to direct circuit modulation,striatal interneurons have also been shown to provide trophic support to maintain neuron populations in adulthood.We discuss this interesting and novel role of striatal interneurons,with a focus on the maintenance of adult dopaminergic neurons from interneuronderived sonic-hedgehog.

Effect of applied electric fields on supralinear dendritic integration of interneuron

Evidences show that electric fields(EFs)induced by the magnetic stimulation could modulates brain activities by regulating the excitability of GABAergic interneuron.However,it is still unclear how and why the EF-induced polarization affects the interneuron response as the interneuron receives NMDA synaptic inputs.Considering the key role of NMDA receptor-mediated supralinear dendritic integration in neuronal computations,we suppose that the applied EFs could functionally modulate interneurons’response via regulating dendritic integration.At first,we build a simplified multi-dendritic circuit model with inhomogeneous extracellular potentials,which characterizes the relationship among EF-induced spatial polarizations,dendritic integration,and somatic output.By performing model-based singular perturbation analysis,it is found that the equilibrium point of fast subsystem can be used to asymptotically depict the subthreshold input–output(sI/O)relationship of dendritic integration.It predicted that EF-induced strong depolarizations on the distal dendrites reduce the dendritic saturation output by reducing driving force of synaptic input,and it shifts the steep change of sI/O curve left by reducing stimulation threshold of triggering NMDA spike.Also,the EF modulation prefers the global dendritic integration with asymmetric scatter distribution of NMDA synapses.Furthermore,we identify the respective contribution of EF-regulated dendritic integration and EF-induced somatic polarization to an action potential generation and find that they have an antagonistic effect on AP generation due to the varied NMDA spike threshold under EF stimulation.

Chx10+V2a interneurons in spinal motor regulation and spinal cord injury

Chx10-expressing V2 a(Chx10+V2 a) spinal interneurons play a large role in the excitatory drive of motoneurons. Chemogenetic ablation studies have demonstrated the essential nature of Chx10+V2 a interneurons in the regulation of locomotor initiation, maintenance, alternation, speed, and rhythmicity. The role of Chx10+V2 a interneurons in locomotion and autonomic nervous system regulation is thought to be robust, but their precise role in spinal motor regulation and spinal cord injury have not been fully explored. The present paper reviews the origin, characteristics, and functional roles of Chx10+V2 a interneurons with an emphasis on their involvement in the pathogenesis of spinal cord injury. The diverse functional properties of these cells have only been substantiated by and are due in large part to their integration in a variety of diverse spinal circuits. Chx10+V2 a interneurons play an integral role in conferring locomotion, which integrates various corticospinal, mechanosensory, and interneuron pathways. Moreover, accumulating evidence suggests that Chx10+V2 a interneurons also play an important role in rhythmic patterning maintenance, leftright alternation of central pattern generation, and locomotor pattern generation in higher order mammals, likely conferring complex locomotion. Consequently, the latest research has focused on postinjury transplantation and noninvasive stimulation of Chx10+V2 a interneurons as a therapeutic strategy, particularly in spinal cord injury. Finally, we review the latest preclinical study advances in laboratory derivation and stimulation/transplantation of these cells as a strategy for the treatment of spinal cord injury. The evidence supports that the Chx10+V2 a interneurons act as a new therapeutic target for spinal cord injury. Future optimization strategies should focus on the viability, maturity, and functional integration of Chx10+V2 a interneurons transplanted in spinal cord injury foci.

Propriospinal interneurons in the spotlight for anatomical and functional recovery after spinal cord injury

Spinal cord injury（SCI）with consecutive paralysis below the lesion level is a severe disorder affecting the patient for the rest of his or her life.So far,there is no known fundamental intervention strategy for efficiently helping those patients regain their motor abilities,despite intense research in this area.Thus,effective treatment for those patients is still an open question. A spinal cord injury is accompanied by a prima- ry, severe and irreversible neuronal cell death in the trauma region, fol- lowed by a secondary extensive cell necrosis in the lesion surrounding areas. Nevertheless, recent studies indicate that regeneration after spinal cord injury could be possible if three substantial steps are fulfilled： （1） reduction of the inhibitory environment at the SCI lesion site, （2） iden- tification of a neural substrate to establish new spinal circuits, and （3） support of these circuits to form permanent, functional motor, sensory, or autonomic connections （Dru and Hoh, 2015）.

Roles of calretinin interneurons in APP / PS1 mouse model

OBJECTIVE To explore the changes of calretinin interneurons in APP/PS1 mouse model and their correlation with the pathological features of Alzheimer disease.METHODS The morphological differences between the brain regions of control and transgenic(TG) mice were detected by Nissl staining.By immunofluorescence histochemistry and western blotting,the expression of related proteins was detected,including GAD65/67,calretinin and Aβ1-42.At the same time,in terms of behavioral experiments,the motor ability,the level of fear and cognitive level of control and transgenic mice were tested through open-field test,elevated plus maze and novel object recognition(NOR) experiment.RESULTS According to Nissl staining results,compared with the control group,the number of cells in glomerular layer(GL) and granule cell layer(GCL) of olfactory bulb in the TG group was significantly reduced.Meanwhile,in the hippocampus,compared with the control group,the ventral CA1 and CA3 is dysplastic in APP/PS1 group.Moreover,the morphology of subgranular zone(SGZ) layer cells in the dorsal DG significantly changed and the number of cells in hilar regions significantly decreased in the TG group.Other brain regions associated with cognition,including the piriform cortex,entorhinal cortex and the prefrontal cortex,showed no significant changes between the control and TG group.By Western blotting experiment,compared with the control mice,it was found that the expression of GAD65/67 and calretinin in the olfactory bulb and hippocampus was significantly decreased in the TG group.In detail,the level of the protein in the relevant brain regions was detected by immunofluorescence histochemistry(IHC).The expression of calretinin in GL of the olfactory bulb and the hippocampal DG region was significantly decreased,which was correlated with the distribution of Aβ1-42 by IHC.In the part of functional behavioral experiment,compared with the control mice,the total distance of movement in 6 M TG group mice was significantly increased in the open field test.In the elevated plus maze test,there were no significant differences between control and TG group.In addition,the mice of TG group lacked the ability to distinguish between old and new objects in the NOR experiment.CONCLUSION The number of calretinin interneurons in olfactory bulb and hippocampus decreased significantly in APP/PS1 mouse model,which is more correlated with the distribution of Aβ1-42 and functional disorders,including the enhancement of spontaneous locomotor activity and cognitive impairment.

Parvalbumin interneurons in anterior cingu⁃late cortex regulate cognitive behaviors in methylazoxymethanol acetate model of schizophrenia

OBJECTIVE Cognitive dysfunc⁃tion is a core disturbance of schizophrenia,appear to emerge from impaired neural activity.The anterior cingulate cortex(ACC)is an integra⁃tion hub for higher-order thalamic inputs impor⁃tant for complex cognitive tasks such as learning and memory processes,attention and social interaction.Parvalbumin(PV)interneurons could filter information at pyramidal neurons of ACC,and the abnormal PV interneurons have been observed in both humans and animal models of schizophrenia.However,the mechanisms of PV interneurons in ACC regulating cognition in schizophrenia is poorly understood.METHODS The pregnant mice were injected with methyl⁃azoxymethanol acetate(MAM)on gestational day(GD)16 for the neurodevelopmental MAM model of schizophrenia in our study.We investi⁃gated the cognitive behaviors by a serious of tests such as pre-pulse inhibition,Y maze,novel object and novel location recognition and the intrinsic excitability of PV interneurons and inhibi⁃tory synaptic transmission onto pyramidal cells localized in layer 5 of ACC by whole-cell record⁃ings.Further,the PV interneurons were regulat⁃ed by designer receptor exclusively activated by a designer drug(DREADD)system and the D-serine,a co-agonist of N-methyl-D-aspartate(NMDA)receptors.RESULTS①MAM mice showed the cognitive deficits and hypo-excitability of PV interneurons in ACC.②Restoration of PV interneuron activity in ACC improved cognitive function in MAM mice.③Inhibition of PV interneu⁃ron activity in ACC was sufficient to cause cogni⁃tive dysfunction in control mice.④NMDA recep⁃tors of PV interneurons in ACC were impaired in MAM mice.⑤Deficits of NMDA receptor sig⁃naling specifically in PV interneurons and of cog⁃nitive behaviors in MAM mice were rescued by D-serine.CONCLUSION PV interneurons in ACC are closely related to cognitive function in the MAM model of schizophrenia and D-serine maybe a potential therapy for schizophrenia.

Psychiatric risk gene transcription factor 4 preferentially regulates cortical interneuron neurogenesis during early brain development

Genetic variants within or near the transcription factor 4 gene(TCF4)are robustly implicated in psychiatric disorders including schizophrenia.However,the biological pleiotropy poses considerable obstacles to dissect the potential relationship between TCF4 and those highly heterogeneous diseases.Through integrative transcriptomic analysis,we demonstrated that TCF4 is preferentially expressed in cortical interneurons during early brain development.Therefore,disruptions of interneuron development might be the underlying contribution of TCF4 perturbation to a range of neurodevelopmental disorders.Here,we performed chromatin immunoprecipitation sequencing(ChIP-seq)of TCF4 on human medial ganglionic eminence-like organoids(hMGEOs)to identify genome-wide TCF4 binding sites,followed by integration of multi-omics data from human fetal brain.We observed preferential expression of the isoform TCF4-B over TCF4-A.De novo motif analysis found that the identified 5916 TCF4 binding sites are significantly enriched for the E-box sequence.The predicted TCF4 targets in general have positively correlated expression levels with TCF4 in the cortical interneurons,and are primarily involved in biological processes related to neurogenesis.Interestingly,we found that TCF4 interacts with non-bHLH proteins such as FOS/JUN,which may underlie the functional specificity of TCF4 in hMGEOs.This study highlights the regulatory role of TCF4 in interneuron development and provides compelling evidence to support the biological rationale linking TCF4 to the developing cortical interneuron and psychiatric disorders.

Population Bursts of Parvalbumin-Positive Interneurons Inhibit Spiking Pyramidal Cells in Spontaneously Active Cortical in Vitro Networks

Author present the interplay between different neuron types in the spontaneous electrical activity of low density cortical in vitro networks grown on MEA （multielectrode arrays） of glass neurochips. In 10% of the networks, the continuously spiking activity of some neurons was inhibited by synchronous bursts or superbursts of the majority of the other neurons. Immunohistochemical staining subsequent to MEA recordings suggest that the synchronously bursting neurons are parvalbumin-positive interneurons with abundant axonal ramifications. Blocking chemical synaptic transmission by Ca2＋-free medium revealed that the curbed spiking neurons are intrinsically active. It is assumed that these neurons are pyramidal cells which may be inhibited by groups of synchronously bursting interneurons. It is propose that the observed burst-induced inhibition is an important principle in the temporal organization of neuronal activity as well as in the restriction of excitation, and thus essential for information processing in the cerebral cortex.

A study on discharge features of interneuron in the hippocampal network

The firing of neurons in the hippocampal network has a close relationship with human memory and learning. In this paper, a numerical simulation of interneurons in the hippocampal network has been operated. It analyzes the influence of external stimulation on firing rhythms. The diversity of firing pattern, especially the circle of unit firing pattern, is shown by ISI.

Dysfunction of hippocampal interneurons in epilepsy

Gamma-amino-butyric acid（GABA）-containing interneurons are crucial to both development and function of the brain. Down-regulation of GABAergic inhibition may result in the generation of epileptiform activity. Loss, axonal sprouting, and dysfunction of interneurons are regarded as mechanisms involved in epileptogenesis. Recent evidence suggests that network connectivity and the properties of interneurons are responsible for excitatory-inhibitory neuronal circuits. The balance between excitation and inhibition in CA1 neuronal circuitry is considerably altered during epileptic changes. This review discusses interneuron diversity, the causes of interneuron dysfunction in epilepsy, and the possibility of using GABAergic neuronal progenitors for the treatment of epilepsy.

Ripple-associated high-firing interneurons in the hippocampal CA1 region

By simultaneously recording the activity of individual neurons and field potentials in freely behaving mice, we found two types of interneurons firing at high frequency in the hippocampal CA1 region, which had high correlations with characteristic sharp wave-associated ripple oscillations (100―250 Hz) during slow-wave sleep. The firing of these two types of interneurons highly synchronized with ripple oscillations during slow-wave sleep, with strongly increased firing rates corresponding to individual ripple episodes. Interneuron type I had at most one spike in each sub-ripple cycle of ripple episodes and the peak firing rate was 310±33.17 Hz. Interneuron type II had one or two spikes in each sub-ripple cycle and the peak firing rate was 410±47.61 Hz. During active exploration, their firing was phase locked to theta oscillations with the highest probability at the trough of theta wave. Both two types of interneurons increased transiently their firing rates responding to the startling shake stimuli. The results showed that these two types of high-frequency interneurons in the hippocampal CA1 region were involved in the modulation of the hippocampal neural network during different states.

Laminar Distribution of Neurochemically-Identified Interneurons and Cellular Co-expression of Molecular Markers in Epileptic Human Cortex

Inhibitory GABAergic interneurons are fundamental elements of cortical circuits and play critical roles in shaping network activity. Dysfunction of interneurons can lead to various brain disorders, including epilepsy,schizophrenia, and anxiety. Based on the electrophysiological properties, cell morphology, and molecular identity,interneurons could be classified into various subgroups. In this study, we investigated the density and laminar distribution of different interneuron types and the coexpression of molecular markers in epileptic human cortex.We found that parvalbumin(PV) and somatostatin(SST)neurons were distributed in all cortical layers except layer I, while tyrosine hydroxylase(TH) and neuropeptide Y(NPY) were abundant in the deep layers and white matter.Cholecystokinin(CCK) neurons showed a high density in layers IV and VI. Neurons with these markers constituted*7.2%(PV), 2.6%(SST), 0.5%(TH), 0.5%(NPY), and4.4%(CCK) of the gray-matter neuron population. Doubleand triple-labeling revealed that NPY neurons were also SST-immunoreactive(97.7%), and TH neurons were more likely to express SST(34.2%) than PV(14.6%). A subpopulation of CCK neurons(28.0%) also expressed PV, but none contained SST. Together, these results revealed the density and distribution patterns of different interneuron populations and the overlap between molecular markers in epileptic human cortex.

GABAergic Interneurons are Required for Generation of Slow CA1 Oscillation in Rat Hippocampus

Neuronal oscillations are fundamental to hip- pocampal function. It has been shown that GABAergic interneurons make an important contribution to hippocampal oscillations, but the underlying mechanism is not well understood. Here, using whole-cell recording in the complete hippocampal formation isolated from rats at postnatal days 14-18, we showed that GABAA receptormediated activity enhanced the generation of slow CA1 oscillations. In vitro, slow oscillations （0.5-1.5 Hz） were generated in CA1 neurons, and they consisted primarily of excitatory rather than inhibitory membrane-potential changes. These oscillations were greatly reduced by blocking GABAA receptor-mediated activity with bicuculline and were enhanced by increasing such activity with midazolam, suggesting that interneurons are required for oscillation generation. Consistently, CA1 fast-spiking interneurons were found to generate action potentials usually preceding those in CA1 pyramidal cells. These findings indicate a GABAA receptor-based mechanism for the generation of the slow CA1 oscillation in the hippocampus.

Neuroligins Differentially Mediate Subtype-Specific Synapse Formation in Pyramidal Neurons and Interneurons

Neuroligins(NLs) are postsynaptic cell-adhesion proteins that play important roles in synapse formation and the excitatory-inhibitory balance. They have been associated with autism in both human genetic and animal model studies, and affect synaptic connections and synaptic plasticity in several brain regions. Yet current research mainly focuses on pyramidal neurons, while the function of NLs in interneurons remains to be understood. To explore the functional difference among NLs in the subtypespecific synapse formation of both pyramidal neurons and interneurons, we performed viral-mediated shRNA knockdown of NLs in cultured rat cortical neurons and examined the synapses in the two major types of neurons. Our results showed that in both types of neurons, NL1 and NL3 were involved in excitatory synapse formation, and NL2 in GABAergic synapse formation. Interestingly, NL1 affectedGABAergic synapse formation more specifically than NL3,and NL2 affected excitatory synapse density preferentially in pyramidal neurons. In summary, our results demonstrated that different NLs play distinct roles in regulating the development and balance of excitatory and inhibitory synapses in pyramidal neurons and interneurons.

Hippocampal Interneurons are Required for Trace Eyeblink Conditioning in Mice

While the hippocampus has been implicated in supporting the association among time-separated events,the underlying cellular mechanisms have not been fully clarified.Here,we combined in vivo multi-channel recording and optogenetics to investigate the activity of hippocampal interneurons in freely-moving mice performing a trace eyeblink conditioning(tEBC)task.We found that the hippocampal interneurons exhibited conditioned stimulus(CS)-evoked sustained activity,which predicted the performance of conditioned eyeblink responses(CRs)in the early acquisition of the tEBC.Consistent with this,greater proportions of hippocampal pyramidal cells showed CS-evoked decreased activity in the early acquisition of the tEBC.Moreover,optogenetic suppression of the sustained activity in hippocampal interneurons severely impaired acquisition of the tEBC.In contrast,suppression of the sustained activity of hippocampal interneurons had no effect on the performance of well-learned CRs.Our findings highlight the role of hippocampal interneurons in the tEBC,and point to a potential cellular mechanism subserving associative learning.

A Whole-brain Map of Long-range Inputs to GABAergic Interneurons in the Mouse Caudal Forelimb Area

The caudal forelimb area(CFA)of the mouse cortex is essential in many forelimb movements,and diverse types of GABAergic interneuron in the CFA are distinct in the mediation of cortical inhibition in motor information processing.However,their long-range inputs remain unclear.In the present study,we combined the monosynaptic rabies virus system with Cre driver mouse lines to generate a whole-brain map of the inputs to three major inhibitory interneuron types in the CFA.We discovered that each type was innervated by the same upstream areas,but there were quantitative differences in the inputs from the cortex,thalamus,and pallidum.Comparing the locations of the interneurons in two subregions of the CFA,we discovered that their long-range inputs were remarkably different in distribution and proportion.This whole-brain mapping indicates the existence of parallel pathway organization in the forelimb subnetwork and provides insight into the inhibitory processes in forelimb movement to reveal the structural architecture underlying the functions of the CFA.

Selective Targeting of Perirhinal Cortex Projection to Hippocampal CA1 Interneurons

Dear Editor,The perirhinal cortex (PER) is conceptually important in the recognition memory, especially in familiarity discrimination, whereas the hippocampus is important for association and recollection [1]. This notion is known as the dualprocess model of recognition memory.

A Critical Role for γCaMKII in Decoding NMDA Signaling to Regulate AMPA Receptors in Putative Inhibitory Interneurons

CaMKII is essential for long-term potentiation(LTP),a process in which synaptic strength is increased following the acquisition of information.Among the four CaMKII isoforms,γCaMKII is the one that mediates the LTP of excitatory synapses onto inhibitory interneurons(LTPE→I).However,the molecular mechanism underlying howγCaMKII mediates LTPE→I remains unclear.Here,we show thatγCaMKII is highly enriched in cultured hippocampal inhibitory interneurons and opts to be activated by higher stimulating frequencies in the 10–30 Hz range.Following stimulation,γCaMKII is translocated to the synapse and becomes co-localized with the postsynaptic protein PSD-95.Knocking downγCaMKII prevents the chemical LTP-induced phosphorylation and trafficking of AMPA receptors(AMPARs)in putative inhibitory interneurons,which are restored by overexpression ofγCaMKII but not its kinase-dead form.Taken together,these data suggest thatγCaMKII decodes NMDAR-mediated signaling and in turn regulates AMPARs for expressing LTP in inhibitory interneurons.

NPR-9 regulates the innate immune response in Caenorhabditis elegans by antagonizing the activity of AIB interneurons

npr-9 encodes a homologue of the gastrin-releasing peptide receptor (GRPR) and is expressed in AIB interneurons. In this study, we investigated the role of NPR-9 in the neuronal control of innate immunity using the model system Caenorhabditis elegans. After exposure to Pseudomonas aeruginosa PA14, npr-9(tm1652) mutants showed resistance to infection, decreased PA14 colonization and increased expression of immunity-related genes. Nematodes overexpressing NPR-9 exhibited increased susceptibility to infection, increased PA14 colonization and reduced expression of immunity-related genes. In nematodes, ChR2-mediated AIB interneuron activation strengthened the innate immune response and decreased PA14 colonization. Overexpression of NPR-9 suppressed the innate immune response and increased PA14 colonization in nematodes with the activation of AIB interneurons mediated by ChR2 or by expressing pkc-1(gf) in AIB interneurons. We, therefore, hypothesize that NPR-9 regulates the innate immune response by antagonizing the activity of AIB interneurons. Furthermore, expression of GRPR, the human homologue of NPR-9, could largely mimic NPR-9 function by regulating innate immunity in nematodes. Our results provide insight into the pivotal role of interneurons in controlling innate immunity and the complex biological functions of GRPRs.

Activation of parvalbumin interneurons in anterior cingulate cortex impairs observational fear

The ability to detect conspecific＇s distress is crucial for animal survival. In rodent models, observational fear （OF） occurs when one animal perceives another fear related negative emotions, which may model certain behaviors caused by witnessing traumatic experiences in humans. Anterior cingulate cortex （ACC） has been showed to play a crucial role in OF. However, cellular and neural circuit basis relating to ACC governing OF is poorly understood. Here, we used Designer Receptor Exclusively Activated by a Designer Drug （DREADD） system to investigate the cell type specific circuit mechanism of ACC in OF. Firstly, inhibitory hM4D （Gi） designer receptor together with clozapine N-oxide （CNO） injection was applied to inactivate ACC neurons in the observer mice. We found that, chemogenetic inhibition of ACC resulted in a decreased freezing response in the observer mice. Next, combining PV-ires-Cre mice and Cre-dependent DREADD system, we selectively targeted the ACC parvalbumin （PV） interneurons with the excitatory hM3D （Gq） designer receptor. Activation of ACC PV interneurons following CNO injection reduced freezing response in the observer mice, while had no effect on freezing response in the demon- strator mice. Finally, monosynaptic rabies retrograde tracing revealed that ACC PV interneurons receive inputs from the mediodorsal thalamic nucleus （MD） and the ventromedial thalamic nucleus （VM）, both known for their roles in OF. Taken together, these findings reveal that ACC activation is important for OF, during which PV interneurons in ACC play an important regulatory role. Abnormal function of ACC PV interneurons might contribute to the pathology of empathy- deficits related diseases, such as autism and schizoohrenia.