Parvalbumin interneuron vulnerability and brain disorders

Investigating 7,8-Dihydroxyflavone to combat maternal immune activation effects on offspring gene expression and behaviour

Infection during pregnancy is a substantial risk factor for the unborn child to develop autism or schizophrenia later in life, and is thought to be driven by maternal immune activation (MIA). MIA can be modelled by exposing pregnant mice to Polyinosinic: polycytidylic acid (Poly-I:C), a viral mimetic that induces an immune response and recapitulates in the offspring many neurochemical features of ASD and schizophrenia, including altered BDNF-TrkB signalling and disruptions to excitatory/inhibitory balance. Therefore, we hypothesised that a BDNF mimetic, 7,8-Dihydroxyflavone (7,8-DHF), administered prophylactically to the dam may prevent the neurobehavioural sequelae of disruptions induced by MIA. Dams were treated with 7,8-DHF in the drinking water (0.08 mg/Ml) from gestational day (GD) 9-20 and were exposed to Poly-I:C at GD17 (20 mg/kg, i.p.). Foetal brains were collected 6 h post Poly-I:C exposure for RT-qPCR analysis of BDNF, cytokine, GABAergic and glutamatergic gene targets. A second adult cohort were tested in a battery of behavioural tests relevant to schizophrenia and the prefrontal cortex and ventral hippocampus dissected for RT-qPCR analysis. Foetal brains exposed to Poly-I:C showed increased IL-6, but reduced expression of Ntrk2 and multiple GABAergic and glutamatergic markers. Anxiety-like behaviour was observed in adult offspring prenatally exposed to poly-I:C, which was accompanied by altered expression of Gria2 in the prefrontal cortex and Gria4 in the ventral hippocampus. While 7-8 DHF normalised the expression of some glutamatergic (Grm5) and GABAergic (Gabra1) genes in Poly-I:C exposed offspring, it also led to substantial alterations in offspring not exposed to Poly-I:C. Furthermore, mice exposed to 7,8-DHF prenatally showed increased pre-pulse inhibition and reduced working memory in adulthood. These data advance understanding of how 7,8-DHF and MIA prenatal exposure impacts genes critical to excitatory/inhibitory pathways and related behaviour.

GluK1 kainate receptors are necessary for functional maturation of parvalbumin interneurons regulating amygdala circuit function

Parvalbumin expressing interneurons (PV INs) are key players in the local inhibitory circuits and their developmental maturation coincides with the onset of adult-type network dynamics in the brain. Glutamatergic signaling regulates emergence of the unique PV IN phenotype, yet the receptor mechanisms involved are not fully understood. Here we show that GluK1 subunit containing kainate receptors (KARs) are necessary for development and maintenance of the neurochemical and functional properties of PV INs in the lateral and basal amygdala (BLA). Ablation of GluK1 expression specifically from PV INs resulted in low parvalbumin expression and loss of characteristic high firing rate throughout development. In addition, we observed reduced spontaneous excitatory synaptic activity at adult GluK1 lacking PV INs. Intriguingly, inactivation of GluK1 expression in adult PV INs was sufficient to abolish their high firing rate and to reduce PV expression levels, suggesting a role for GluK1 in dynamic regulation of PV IN maturation state. The PV IN dysfunction in the absence of GluK1 perturbed the balance between evoked excitatory vs. inhibitory synaptic inputs and long-term potentiation (LTP) in LA principal neurons, and resulted in aberrant development of the resting-state functional connectivity between mPFC and BLA. Behaviorally, the absence of GluK1 from PV INs associated with hyperactivity and increased fear of novelty. These results indicate a critical role for GluK1 KARs in regulation of PV IN function across development and suggest GluK1 as a potential therapeutic target for pathologies involving PV IN malfunction.

Integrated platform for multiscale molecular imaging and phenotyping of the human brain

Understanding cellular architectures and their connectivity is essential for interrogating system function and dysfunction. However, we lack technologies for mapping the multiscale details of individual cells and their connectivity in the human organ-scale system. We developed a platform that simultaneously extracts spatial, molecular, morphological, and connectivity information of individual cells from the same human brain. The platform includes three core elements: a vibrating microtome for ultraprecision slicing of large-scale tissues without losing cellular connectivity (MEGAtome), a polymer hydrogel-based tissue processing technology for multiplexed multiscale imaging of human organ-scale tissues (mELAST), and a computational pipeline for reconstructing three-dimensional connectivity across multiple brain slabs (UNSLICE). We applied this platform for analyzing human Alzheimer's disease pathology at multiple scales and demonstrating scalable neural connectivity mapping in the human brain.

NARP-related alterations in the excitatory and inhibitory circuitry of socially isolated mice: developmental insights and implications for autism spectrum disorder

Background

Social isolation during critical periods of development is associated with alterations in behavior and neuronal circuitry. This study aimed to investigate the immediate and developmental effects of social isolation on firing properties, neuronal activity-regulated pentraxin (NARP) and parvalbumin (PV) expression in the prefrontal cortex (PFC), social behavior in juvenile socially isolated mice, and the biological relevance of NARP expression in autism spectrum disorder (ASD).

Methods

Mice were subjected to social isolation during postnatal days 21-35 (P21-P35) and were compared with group-housed control mice. Firing properties in the PFC pyramidal neurons were altered in P35 socially isolated mice, which might be associated with alterations in NARP and PV expression.

Results

In adulthood, mice that underwent juvenile social isolation exhibited difficulty distinguishing between novel and familiar mice during a social memory task, while maintaining similar levels of social interaction as the control mice. Furthermore, a marked decrease in NARP expression in lymphoblastoid cell lines derived from adolescent humans with ASD as compared to typically developing (TD) humans was found.

Conclusion

Our study highlights the role of electrophysiological properties, as well as NARP and PV expression in the PFC in mediating the developmental consequences of social isolation on behavior.

Decoding frontotemporal and cell-type-specific vulnerabilities to neuropsychiatric disorders and psychoactive drugs

Frontotemporal lobe abnormalities are linked to neuropsychiatric disorders and cognition, but the role of cellular heterogeneity between temporal lobe (TL) and frontal lobe (FL) in the vulnerability to genetic risk factors remains to be elucidated. We integrated single-nucleus transcriptome analysis in 'fresh' human FL and TL with genetic susceptibility, gene dysregulation in neuropsychiatric disease and psychoactive drug response data. We show how intrinsic differences between TL and FL contribute to the vulnerability of specific cell types to both genetic risk factors and psychoactive drugs. Neuronal populations, specifically PVALB neurons, were most highly vulnerable to genetic risk factors for psychiatric disease. These psychiatric disease-associated genes were mostly upregulated in the TL, and dysregulated in the brain of patients with obsessive-compulsive disorder, bipolar disorder and schizophrenia. Among these genes, GRIN2A and SLC12A5, implicated in schizophrenia and bipolar disorder, were significantly upregulated in TL PVALB neurons and in psychiatric disease patients' brain. PVALB neurons from the TL were twofold more vulnerable to psychoactive drugs than to genetic risk factors, showing the influence and specificity of frontotemporal lobe differences on cell vulnerabilities. These studies provide a cell type resolved map of the impact of brain regional differences on cell type vulnerabilities in neuropsychiatric disorders.

Dopamine neuron degeneration in the Ventral Tegmental Area causes hippocampal hyperexcitability in experimental Alzheimer's Disease

Early and progressive dysfunctions of the dopaminergic system from the Ventral Tegmental Area (VTA) have been described in Alzheimer's Disease (AD). During the long pre-symptomatic phase, alterations in the function of Parvalbumin interneurons (PV-INs) are also observed, resulting in cortical hyperexcitability represented by subclinical epilepsy and aberrant gamma-oscillations. However, it is unknown whether the dopaminergic deficits contribute to brain hyperexcitability in AD. Here, using the Tg2576 mouse model of AD, we prove that reduced hippocampal dopaminergic innervation, due to VTA dopamine neuron degeneration, impairs PV-IN firing and gamma-waves, weakens the inhibition of pyramidal neurons and induces hippocampal hyperexcitability via lower D2-receptor-mediated activation of the CREB-pathway. These alterations coincide with reduced PV-IN numbers and Perineuronal Net density. Importantly, L-DOPA and the selective D2-receptor agonist quinpirole rescue p-CREB levels and improve the PV-IN-mediated inhibition, thus reducing hyperexcitability. Moreover, similarly to quinpirole, sumanirole - another D2-receptor agonist and a known anticonvulsant - not only increases p-CREB levels in PV-INs but also restores gamma-oscillations in Tg2576 mice. Conversely, blocking the dopaminergic transmission with sulpiride (a D2-like receptor antagonist) in WT mice reduces p-CREB levels in PV-INs, mimicking what occurs in Tg2576. Overall, these findings support the hypothesis that the VTA dopaminergic system integrity plays a key role in hippocampal PV-IN function and survival, disclosing a relevant contribution of the reduced dopaminergic tone to aberrant gamma-waves, hippocampal hyperexcitability and epileptiform activity in early AD.

Overexpression of the schizophrenia risk gene C4 in PV cells drives sex-dependent behavioral deficits and circuit dysfunction

Fast-spiking parvalbumin (PV)-positive cells are key players in orchestrating pyramidal neuron activity, and their dysfunction is consistently observed in myriad brain diseases. To understand how immune complement dysregulation - a prevalent locus of brain disease etiology - in PV cells may drive disease pathogenesis, we have developed a transgenic mouse line that permits cell-type specific overexpression of the schizophrenia-associated complement component 4 (C4) gene. We found that overexpression of mouse C4 (mC4) in PV cells causes sex-specific behavioral alterations and concomitant deficits in synaptic connectivity and excitability of PV cells of the prefrontal cortex. Using a computational network, we demonstrated that these microcircuit deficits led to hyperactivity and disrupted neural communication. Finally, pan-neuronal overexpression of mC4 failed to evoke the same deficits in behavior as PV-specific mC4 overexpression, suggesting that C4 perturbations in fast-spiking neurons are more harmful to brain function than pan-neuronal alterations. Together, these results provide a causative link between C4 and the vulnerability of PV cells in brain disease.

Native-state proteomics of Parvalbumin interneurons identifies unique molecular signatures and vulnerabilities to early Alzheimer's pathology

Dysfunction in fast-spiking parvalbumin interneurons (PV-INs) may represent an early pathophysiological perturbation in Alzheimer's Disease (AD). Defining early proteomic alterations in PV-INs can provide key biological and translationally-relevant insights. We used cell-type-specific in-vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state PV-IN proteomes. PV-IN proteomic signatures include high metabolic and translational activity, with over-representation of AD-risk and cognitive resilience-related proteins. In bulk proteomes, PV-IN proteins were associated with cognitive decline in humans, and with progressive neuropathology in humans and the 5xFAD mouse model of Aβ pathology. PV-IN CIBOP in early stages of Aβ pathology revealed signatures of increased mitochondria and metabolism, synaptic and cytoskeletal disruption and decreased mTOR signaling, not apparent in whole-brain proteomes. Furthermore, we demonstrated pre-synaptic defects in PV-to-excitatory neurotransmission, validating our proteomic findings. Overall, in this study we present native-state proteomes of PV-INs, revealing molecular insights into their unique roles in cognitive resiliency and AD pathogenesis.

NADPH-oxidases as potential pharmacological targets for thrombosis and depression comorbidity

There is a complex interrelationship between the nervous system and the cardiovascular system. Comorbidities of cardiovascular diseases (CVD) with mental disorders, and vice versa, are prevalent. Adults with mental disorders such as anxiety and depression have a higher risk of developing CVD, and people with CVD have an increased risk of being diagnosed with mental disorders. Oxidative stress is one of the many pathways associated with the pathophysiology of brain and cardiovascular disease. Nicotinamide adenine dinucleotide phosphate oxidase (NOX) is one of the major generators of reactive oxygen species (ROS) in mammalian cells, as it is the enzyme that specifically produces superoxide. This review summarizes recent findings on the consequences of NOX activation in thrombosis and depression. It also discusses the therapeutic effects and pharmacological strategies of NOX inhibitors in CVD and brain disorders. A better comprehension of these processes could facilitate the development of new therapeutic approaches for the prevention and treatment of the comorbidity of thrombosis and depression.

Human chorionic gonadotropin decreases cerebral cystic encephalomalacia and parvalbumin interneuron degeneration in a pro-inflammatory model of mouse neonatal hypoxia-ischemia

The pregnancy hormone, human chorionic gonadotropin (hCG) is an immunoregulatory and neurotrophic glycoprotein of potential clinical utility in the neonate at risk for cerebral injury. Despite its well-known role in its ability to modulate the innate immune response during pregnancy, hCG has not been demonstrated to affect the pro-degenerative actions of inflammation in neonatal hypoxia-ischemia (HI). Here we utilize a neonatal mouse model of mild HI combined with intraperitoneal administration of lipopolysaccharide (LPS) to evaluate the neuroprotective actions of hCG in the setting of endotoxin-mediated systemic inflammation. Intraperitoneal treatment of hCG shortly prior to LPS injection significantly decreased tissue loss and cystic degeneration in the hippocampal and cerebral cortex in the term-equivalent neonatal mouse exposed to mild HI. Noting that parvalbumin immunoreactive interneurons have been broadly implicated in neurodevelopmental disorders, it is notable that hCG significantly improved the injury-mediated reduction of these neurons in the cerebral cortex, striatum and hippocampus. The above findings were associated with a decrease in the amount of Iba1 immunoreactive microglia in most of these brain regions. These observations implicate hCG as an agent capable of improving the neurological morbidity associated with peripheral inflammation in the neonate affected by HI. Future preclinical studies should aim at demonstrating added neuroprotective benefit by hCG in the context of therapeutic hypothermia and further exploring the mechanisms responsible for this effect. This research is likely to advance the therapeutic role of gonadotropins as a treatment for neonates with neonatal brain injury.

Adolescent Stress-Induced Ventral Hippocampus Redox Dysregulation Underlies Behavioral Deficits and Excitatory/Inhibitory Imbalance Related to Schizophrenia

BACKGROUND AND HYPOTHESIS

Redox dysregulation has been proposed as a convergent point of childhood trauma and the emergence of psychiatric disorders, such as schizophrenia (SCZ). A critical region particularly vulnerable to environmental insults during adolescence is the ventral hippocampus (vHip). However, the impact of severe stress on vHip redox states and their functional consequences, including behavioral and electrophysiological changes related to SCZ, are not entirely understood.

STUDY DESIGN

After exposing adolescent animals to physical stress (postnatal day, PND31-40), we explored social and cognitive behaviors (PND47-49), the basal activity of pyramidal glutamate neurons, the number of parvalbumin (PV) interneurons, and the transcriptomic signature of the vHip (PND51). We also evaluated the impact of stress on the redox system, including mitochondrial respiratory function, reactive oxygen species (ROS) production, and glutathione (GSH) levels in the vHip and serum.

STUDY RESULTS

Adolescent-stressed animals exhibited loss of sociability, cognitive impairment, and vHip excitatory/inhibitory (E/I) imbalance. Genome-wide transcriptional profiling unveiled the impact of stress on redox system- and synaptic-related genes. Stress impacted mitochondrial respiratory function and changes in ROS levels in the vHip. GSH and glutathione disulfide (GSSG) levels were elevated in the serum of stressed animals, while GSSG was also increased in the vHip and negatively correlated with sociability. Additionally, PV interneuron deficits in the vHip caused by adolescent stress were associated with oxidative stress.

CONCLUSIONS

Our results highlight the negative impact of adolescent stress on vHip redox regulation and mitochondrial function, which are partially associated with E/I imbalance and behavioral abnormalities related to SCZ.

Human mutations in SLITRK3 implicated in GABAergic synapse development in mice

This study reports on biallelic homozygous and monoallelic de novo variants in SLITRK3 in three unrelated families presenting with epileptic encephalopathy associated with a broad neurological involvement characterized by microcephaly, intellectual disability, seizures, and global developmental delay. SLITRK3 encodes for a transmembrane protein that is involved in controlling neurite outgrowth and inhibitory synapse development and that has an important role in brain function and neurological diseases. Using primary cultures of hippocampal neurons carrying patients' SLITRK3 variants and in combination with electrophysiology, we demonstrate that recessive variants are loss-of-function alleles. Immunostaining experiments in HEK-293 cells showed that human variants C566R and E606X change SLITRK3 protein expression patterns on the cell surface, resulting in highly accumulating defective proteins in the Golgi apparatus. By analyzing the development and phenotype of SLITRK3 KO (SLITRK3-/-) mice, the study shows evidence of enhanced susceptibility to pentylenetetrazole-induced seizure with the appearance of spontaneous epileptiform EEG as well as developmental deficits such as higher motor activities and reduced parvalbumin interneurons. Taken together, the results exhibit impaired development of the peripheral and central nervous system and support a conserved role of this transmembrane protein in neurological function. The study delineates an emerging spectrum of human core synaptopathies caused by variants in genes that encode SLITRK proteins and essential regulatory components of the synaptic machinery. The hallmark of these disorders is impaired postsynaptic neurotransmission at nerve terminals; an impaired neurotransmission resulting in a wide array of (often overlapping) clinical features, including neurodevelopmental impairment, weakness, seizures, and abnormal movements. The genetic synaptopathy caused by SLITRK3 mutations highlights the key roles of this gene in human brain development and function.

Perineuronal net structure as a non-cellular mechanism contributing to affective state: A scoping review

Affective state encompasses emotional responses to our physiology and influences how we perceive and respond within our environment. In affective disorders such as depression, cognitive adaptability is challenged, and structural and functional brain changes have been identified. However, an incomplete understanding persists of the molecular and cellular mechanisms at play in affective state. An exciting area of newly appreciated importance is perineuronal nets (PNNs); a specialised component of extracellular matrix playing a critical role in neuroprotection and synaptic plasticity. A scoping review found 24 studies demonstrating that PNNs are still a developing field of research with a promising general trend for stress in adulthood to increase the intensity of PNNs, whereas stress in adolescence reduced (potentially developmentally delayed) PNN numbers and intensity, while antidepressants correlated with reduced PNN numbers. Despite promising trends, limited research underscores the need for further exploration, emphasizing behavioral outcomes for validating affective states. Understanding PNNs' role may offer therapeutic insights for depression and inform biomarker development, advancing precision medicine and enhancing well-being.

Hippocampal parvalbumin and perineuronal nets: Possible involvement in anxiety-like behavior in rats

The excitatory-inhibitory imbalance has been considered an important mechanism underlying stress-related psychiatric disorders. In the present study, rats were exposed to 6 days of inescapable foot shock (IFS) to induce stress. The open field test and elevated plus maze test showed that IFS-exposed rats exhibited increased anxiety-like behavior. Immunofluorescence showed that IFS rats had a decreased density of GAD67-immunoreactive interneurons in the dorsal hippocampal CA1 region, while no significant change in the density of CaMKIIα-immunoreactive glutamatergic neurons was seen. We investigated the expression of different interneuron subtype markers, including parvalbumin (PV), somatostatin (SST), and calretinin (CR), and noted a marked decline in the density of PV-immunoreactive interneurons in the dorsal CA1 region of IFS rats. The perineuronal net (PNN) is a specialized extracellular matrix structure primarily around PV interneurons. We used Wisteria floribunda agglutinin lectin to label the PNNs and observed that IFS rats had an increased proportion of PNN-coated PV-positive interneurons in CA1. The number of PSD95-positive excitatory synaptic puncta on the soma of PNN-free PV-positive interneurons was significantly higher than that of PNN-coated PV-positive interneurons. Our findings suggest that the effect of IFS on the hippocampal GABAergic interneurons could be cell-type-specific. Loss of PV phenotype in the dorsal hippocampal CA1 region may contribute to anxiety in rats. The dysregulated PV-PNN relationship in CA1 after traumatic stress exposure might represent one of the neurobiological correlates of the observed anxiety-like behavior.

Treadmill exercise improves hippocampal neural plasticity and relieves cognitive deficits in a mouse model of epilepsy

Epilepsy frequently leads to cognitive dysfunction and approaches to treatment remain limited. Although regular exercise effectively improves learning and memory functions across multiple neurological diseases, its application in patients with epilepsy remains controversial. Here, we adopted a 14-day treadmill-exercise paradigm in a pilocarpine injection-induced mouse model of epilepsy. Cognitive assays confirmed the improvement of object and spatial memory after endurance training, and electrophysiological studies revealed the maintenance of hippocampal plasticity as a result of physical exercise. Investigations of the mechanisms underlying this effect revealed that exercise protected parvalbumin interneurons, probably via the suppression of neuroinflammation and improved integrity of blood-brain barrier. In summary, this work identified a previously unknown mechanism through which exercise improves cognitive rehabilitation in epilepsy.

Enhanced anxiety-like behavior induced by chronic neuropathic pain and related parvalbumin-positive neurons in male rats

Anxiety commonly co-occurs with and exacerbates pain, but the interaction between pain progression and anxiety, and its underlying mechanisms remain unclear. Inhibitory interneurons play a crucial role in maintaining normal central nervous system function and are suggested to be involved in pain-induced anxiety. This study aimed to elucidate the time-dependent effects of neuropathic pain on the developmental anxiety-like behaviors and related inhibitory interneurons; parvalbumin (PV)- and cholecystokinin (CCK)-positive neurons in corticolimbic regions. Using an 8-week-old male Wistar rat model with partial sciatic nerve ligation (pSNL), anxiety-like behaviors were biweekly assessed post-surgery through open field (OF) and elevated plus maze (EPM) tests. From 4 weeks post-surgery, pSNL rats exhibited reduced OF center time, rearing, and initial activity, along with diminished EPM open-arm activities (time spent, head dips, movement, and rearing), which correlated with the paw withdrawal threshold. These effects were absent at 2 weeks post-surgery. At 8 weeks post-surgery, specific behaviors (decreased total rearing and increased inactive time in EPM) were observed in the pSNL group. Immunohistochemistry revealed changes in PV- and CCK-positive neurons in specific corticolimbic subregions of pSNL rats at 8 weeks post-surgery. Notably, PV-positive neuron densities in the basolateral amygdaloid complex (BLC) and hippocampal cornu ammonis areas 1 and 2 correlated with anxiety-like behavioral parameters. PV-positive neurons in the BLC of pSNL rats were predominantly changed in large-cell subtypes and were less activated. These findings indicate that anxiety-like behaviors emerge in the late phase of neuropathic pain and relate to PV-positive neurons in corticolimbic regions of pSNL rats.

Use of Post-mortem Brain Tissue in Investigations of Obsessive- Compulsive Disorder: A Systematic Review

BACKGROUND

Post-mortem examination of the brain is a key strategy to increase our understanding of the neurobiology of mental disorders. While extensive post-mortem research has been undertaken on some mental disorders, others appear to have been relatively neglected.

OBJECTIVE

The objective of the study was to conduct a systematic review of post-mortem research on obsessive-compulsive disorder (OCD).

METHODS

A systematic review was performed in accordance with PRISMA guidelines to provide an overview of quantitative, qualitative, or mixed methods primary research studies on OCD. Search platforms included NCBI Pubmed, SCOPUS, and Web of Science.

RESULTS

A total of 52 publications were found, and after the removal of works not meeting the inclusion criteria, six (6) peer-reviewed publications remained. These post-mortem studies have provided data on DNA methylation, cellular and molecular alterations, and gene expression profiling in brain areas associated with OCD.

DISCUSSION AND CONCLUSION

Included studies highlight the potential value of post-mortem brains from well-characterized individuals with OCD and suggest the need for additional work in this area.

Prefrontal and Hippocampal Parvalbumin Interneurons in Animal Models for Schizophrenia: A Systematic Review and Meta-analysis

BACKGROUND

Consistent with postmortem findings in patients, most animal models for schizophrenia (SCZ) present abnormal levels of parvalbumin (PV), a marker of fast-spiking GABAergic interneurons, in the prefrontal cortex (PFC) and hippocampus (HIP). However, there are discrepancies in the literature. PV reductions lead to a functional loss of PV interneurons, which is proposed to underly SCZ symptoms. Given its complex etiology, different categories of animal models have been developed to study SCZ, which may distinctly impact PV levels in rodent brain areas.

STUDY DESIGN

We performed a quantitative meta-analysis on PV-positive cell number/density and expression levels in the PFC and HIP of animal models for SCZ based on pharmacological, neurodevelopmental, and genetic manipulations.

RESULTS

Our results confirmed that PV levels are significantly reduced in the PFC and HIP regardless of the animal model. By categorizing into subgroups, we found that all pharmacological models based on NMDA receptor antagonism decreased PV-positive cell number/density or PV expression levels in both brain areas examined. In neurodevelopmental models, abnormal PV levels were confirmed in both brain areas in maternal immune activation models and HIP of the methylazoxymethanol acetate model. In genetic models, negative effects were found in neuregulin 1 and ERBB4 mutant mice in both brain regions and the PFC of dysbindin mutant mice. Regarding sex differences, male rodents exhibited PV reductions in both brain regions only in pharmacological models, while few studies have been conducted in females.

CONCLUSION

Overall, our findings support deficits in prefrontal and hippocampal PV interneurons in animal models for SCZ.

Parvalbumin interneurons dysfunction is potentially associated with FαMNs decrease and NRG1-ErbB4 signaling inhibition in spinal cord in amyotrophic lateral sclerosis

OBJECTIVE

To investigate the alteration of PV interneurons in ALS mainly focusing its dynamic changes and its relationship with motor neurons and ErbB4 signaling.

METHODS

SOD1G93A mice were used as ALS model. ALS animals were divided into different groups according to birth age: symptomatic prophase (50~60 days), symptomatic phase (90~100 days), and symptomatic progression (130~140 days). Immunofluorescence was performed for measurement of PV-positive interneurons, MMP-9, ChAT, NeuN and ErbB4. RT-qPCR and western blot were used to determine the expression of PV and MMP-9.

RESULTS

PV expression was remarkably higher in the anterior horn of gray matter compared with posterior horn and area in the middle of gray matter in control mice. In ALS mice, PV, MMP-9 and ErbB4 levels were gradually decreased along with onset. PV, MMP-9 and ErbB4 levels in ALS mice were significantly down-regulated than control mice after onset, indicating the alteration of PV interneurons, FαMNs and ErbB4. SαMNs levels only decreased remarkably at symptomatic progression in ALS mice compared with control mice, while γMNs levels showed no significant change during whole period in all mice. MMP-9 and ErbB4 were positively correlated with PV. NRG1 treatment significantly enhanced the expression of ErBb4, PV and MMP-9 in ALS mice.

CONCLUSION

PV interneurons decrease is along with FαMNs and ErbB4 decrease in ALS mice.

Calcium-binding protein parvalbumin in the spinal cord and dorsal root ganglia

Parvalbumin is one of the calcium-binding proteins. In the spinal cord, it is mainly expressed in inhibitory neurons; in the dorsal root ganglia, it is expressed in proprioceptive neurons. In contrast to in the brain, weak systematization of parvalbumin-expressing neurons occurs in the spinal cord. The aim of this paper is to provide a systematic review of parvalbumin-expressing neuronal populations throughout the spinal cord and the dorsal root ganglia of mammals, regarding their mapping, co-expression with some functional markers. The data reviewed are mostly concerning rodentia species because they are predominantly presented in literature.

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

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

Parvalbumin as a sex-specific target in Alzheimer's disease research - A mini-review

Alzheimer's disease (AD) is the most common form of dementia, and both the incidence of this disease and its associated cognitive decline disproportionally effect women. While the etiology of AD is unknown, recent work has demonstrated that the balance of excitatory and inhibitory activity across the brain may serve as a strong predictor of cognitive impairments in AD. Across the cortex, the most prominent source of inhibitory signalling is from a class of parvalbumin-expressing interneurons (PV+). In this mini-review, the impacts of sex- and age-related factors on the function of PV+ neurons are examined within the context of vulnerability to AD pathology. These primary factors of influence include changes in brain metabolism, circulating sex hormone levels, and inflammatory response. In addition to positing the increased vulnerability of PV+ neurons to dysfunction in AD, this mini-review highlights the critical importance of presenting sex stratified data in the study of AD.

DOT1L deletion impairs the development of cortical parvalbumin-expressing interneurons

The cortical plate (CP) is composed of excitatory and inhibitory neurons, the latter of which originate in the ganglionic eminences. From their origin in the ventral telencephalon, maturing postmitotic interneurons migrate during embryonic development over some distance to reach their final destination in the CP. The histone methyltransferase Disruptor of Telomeric Silencing 1-like (DOT1L) is necessary for proper CP development and layer distribution of glutamatergic neurons. However, its specific role on cortical interneuron development has not yet been explored. Here, we demonstrate that DOT1L affects interneuron development in a cell autonomous manner. Deletion of Dot1l in Nkx2.1-expressing interneuron precursor cells results in an overall reduction and altered distribution of GABAergic interneurons in the CP from postnatal day 0 onwards. We observed an altered proportion of GABAergic interneurons in the cortex, with a significant decrease in parvalbumin-expressing interneurons. Moreover, a decreased number of mitotic cells at the embryonic day E14.5 was observed upon Dot1l deletion. Altogether, our results indicate that reduced numbers of cortical interneurons upon DOT1L deletion result from premature cell cycle exit, but effects on postmitotic differentiation, maturation, and migration are likely at play as well.

Resveratrol Attenuates Chronic Unpredictable Mild Stress-Induced Alterations in the SIRT1/PGC1α/SIRT3 Pathway and Associated Mitochondrial Dysfunction in Mice

Environmental challenges, specifically chronic stress, have long been associated with neuropsychiatric disorders, including anxiety and depression. Sirtuin-1 (SIRT1) is a NAD+-dependent deacetylase that is widely distributed in the cortex and is involved in stress responses and neuropsychiatric disorders. Nevertheless, how chronic stress modulates the SIRT1 pathway and associated signaling remains unclear. In this study, we first explored the impact of chronic unpredictable mild stress (CUMS) on the SIRT1/PGC1α/SIRT3 pathway, on GABAergic mechanisms, and on mitophagy, autophagy and apoptosis in mice. We also asked whether activation of SIRT1 by resveratrol (RSV) can attenuate CUMS-induced molecular and behavioral alterations. Two-month-old C57/BL6J mice were subjected to three weeks of CUMS and one week of RSV treatment (30 mg/kg; i.p.) during the third week of CUMS. CUMS caused downregulation of the SIRT1/PGC1α/SIRT3 pathway leading to impaired mitochondrial morphology and function. CUMS also resulted in a reduction in numbers of parvalbumin-positive interneurons and increased oxidative stress leading to reduced expression of autophagy- and mitophagy-related proteins. Strikingly, activation of SIRT1 by RSV ameliorated expression of SIRT1/PGC1α/SIRT3, and also improved mitochondrial function, GABAergic mechanisms, mitophagy, autophagy and apoptosis. RSV also rescued CUMS-induced anxiety-like and depressive-like behavior in mice. Our results raise the compelling possibility that RSV treatment might be a viable therapeutic method of blocking stress-induced behavioral alterations.

Distinct patterns of GABAergic interneuron pathology in autism are associated with intellectual impairment and stereotypic behaviors

LAY ABSTRACT

Autism spectrum disorder is a neurodevelopmental condition characterized by deficits in sociability and communication and the presence of repetitive behaviors. How specific pathological alterations of the brain contribute to the clinical profile of autism spectrum disorder remains unknown. We previously found that a specific type of inhibitory interneuron is reduced in number in the autism spectrum disorder prefrontal cortex. Here, we assessed the relationship between interneuron reduction and autism spectrum disorder symptom severity. We collected clinical records from autism spectrum disorder (n = 20) and assessed the relationship between the severity of symptoms and interneuron number. We found that the reduced number of inhibitory interneurons that we previously reported is linked to specific symptoms of autism spectrum disorder, particularly stereotypic movements and intellectual impairments.

Valproate-induced murine autism spectrum disorder is associated with dysfunction of amygdala parvalbumin interneurons and downregulation of AMPK/SIRT1/PGC1α signaling

Autism spectrum disorder (ASD) is a neurodevelopmental condition that is characterized by difficulty in social behavior and restricted behaviors. Also, in ASD, several accompanying disorders such as anxiety are observed. Considering the important role of amygdala in the pathophysiology of ASD, the present study focused on the neuronal changes and it possible signaling pathway in amygdala. After prenatal exposure to valproate (VPA; 600 mg/kg, i.p, on embryonic day 12.5), amount of ROS, MMP, caspase-3 activity, AMPK, SIRT1 and PGC1α proteins, and parvalbumin interneurons in the amygdala were assessed following evaluation of ASD and anxiety-like behaviors. Amygdala analysis revealed ROS accumulation and decreased MMP in autistic rats. In addition, caspase-3 activation elevated and immunoreactivity for parvalbumin interneurons decreased. These were accompanied by anxiety and autistic-like behaviors in open field test, elevated zero maze and U-Shaped 2 Choice Field maze. Also, our data showed that in the valproate group, protein levels of AMPK, SIRT1 and PGC1α reduced. Collectively, our results indicate that prenatal exposure to valproate leads to anxiety and autistic-like behaviors, partly through its targeting amygdala parvalbumin interneurons dysfunction and this might be affected by disturbed AMPK/SIRT1/PGC1α signaling pathway.

Parvalbumin - Positive Neurons in the Neocortex: A Review

The calcium binding protein parvalbumin (PV) in the mammalian neocortex is expressed in a subpopulation of cortical GABAergic inhibitory interneurons. PV - producing interneurons represent the largest subpopulation of neocortical inhibitory cells, exhibit mutual chemical and electrical synaptic contacts and are well known to generate gamma oscillation. This review summarizes basic data of the distribution, afferent and efferent connections and physiological properties of parvalbumin expressing neurons in the neocortex. Basic data about participation of PV-positive neurons in cortical microcircuits are presented. Autaptic connections, metabolism and perineuronal nets (PNN) of PV positive neurons are also discussed.

Differential expression of GABAA receptor subunits δ and α6 mediates tonic inhibition in parvalbumin and somatostatin interneurons in the mouse hippocampus

Inhibitory γ-aminobutyric acid (GABA)-ergic interneurons mediate inhibition in neuronal circuitry and support normal brain function. Consequently, dysregulation of inhibition is implicated in various brain disorders. Parvalbumin (PV) and somatostatin (SST) interneurons, the two major types of GABAergic inhibitory interneurons in the hippocampus, exhibit distinct morpho-physiological properties and coordinate information processing and memory formation. However, the molecular mechanisms underlying the specialized properties of PV and SST interneurons remain unclear. This study aimed to compare the transcriptomic differences between these two classes of interneurons in the hippocampus using the ribosome tagging approach. The results revealed distinct expressions of genes such as voltage-gated ion channels and GABAA receptor subunits between PV and SST interneurons. Gabrd and Gabra6 were identified as contributors to the contrasting tonic GABAergic inhibition observed in PV and SST interneurons. Moreover, some of the differentially expressed genes were associated with schizophrenia and epilepsy. In conclusion, our results provide molecular insights into the distinct roles of PV and SST interneurons in health and disease.

Post-weaning social isolation in male mice leads to abnormal aggression and disrupted network organization in the prefrontal cortex: Contribution of parvalbumin interneurons with or without perineuronal nets

Adverse social experiences during childhood increase the risk of developing aggression-related psychopathologies. The prefrontal cortex (PFC) is a key regulator of social behavior, where experience-dependent network development is tied to the maturation of parvalbumin-positive (PV+) interneurons. Maltreatment in childhood could impact PFC development and lead to disturbances in social behavior during later life. However, our knowledge regarding the impact of early-life social stress on PFC operation and PV+ cell function is still scarce. Here, we used post-weaning social isolation (PWSI) to model early-life social neglect in mice and to study the associated neuronal changes in the PFC, additionally distinguishing between the two main subpopulations of PV+ interneurons, i.e. those without or those enwrapped by perineuronal nets (PNN). For the first time to such detailed extent in mice, we show that PWSI induced disturbances in social behavior, including abnormal aggression, excessive vigilance and fragmented behavioral organization. PWSI mice showed altered resting-state and fighting-induced co-activation patterns between orbitofrontal and medial PFC (mPFC) subregions, with a particularly highly elevated activity in the mPFC. Surprisingly, aggressive interaction was associated with a higher recruitment of mPFC PV+ neurons that were surrounded by PNN in PWSI mice that seemed to mediate the emergence of social deficits. PWSI did not affect the number of PV+ neurons and PNN density, but enhanced PV and PNN intensity as well as cortical and subcortical glutamatergic drive onto mPFC PV+ neurons. Our results suggest that the increased excitatory input of PV+ cells could emerge as a compensatory mechanism for the PV+ neuron-mediated impaired inhibition of mPFC layer 5 pyramidal neurons, since we found lower numbers of GABAergic PV+ puncta on the perisomatic region of these cells. In conclusion, PWSI leads to altered PV-PNN activity and impaired excitatory/inhibitory balance in the mPFC, which possibly contributes to social behavioral disruptions seen in PWSI mice. Our data advances our understanding on how early-life social stress can impact the maturing PFC and lead to the development of social abnormalities in adulthood.

Native-state proteomics of Parvalbumin interneurons identifies novel molecular signatures and metabolic vulnerabilities to early Alzheimer's disease pathology

One of the earliest pathophysiological perturbations in Alzheimer's Disease (AD) may arise from dysfunction of fast-spiking parvalbumin (PV) interneurons (PV-INs). Defining early protein-level (proteomic) alterations in PV-INs can provide key biological and translationally relevant insights. Here, we use cell-type-specific in vivo biotinylation of proteins (CIBOP) coupled with mass spectrometry to obtain native-state proteomes of PV interneurons. PV-INs exhibited proteomic signatures of high metabolic, mitochondrial, and translational activity, with over-representation of causally linked AD genetic risk factors. Analyses of bulk brain proteomes indicated strong correlations between PV-IN proteins with cognitive decline in humans, and with progressive neuropathology in humans and mouse models of Aβ pathology. Furthermore, PV-IN-specific proteomes revealed unique signatures of increased mitochondrial and metabolic proteins, but decreased synaptic and mTOR signaling proteins in response to early Aβ pathology. PV-specific changes were not apparent in whole-brain proteomes. These findings showcase the first native state PV-IN proteomes in mammalian brain, revealing a molecular basis for their unique vulnerabilities in AD.

Cognitive impairment in schizophrenia: aetiology, pathophysiology, and treatment

Cognitive deficits are a core feature of schizophrenia, account for much of the impaired functioning associated with the disorder and are not responsive to existing treatments. In this review, we first describe the clinical presentation and natural history of these deficits. We then consider aetiological factors, highlighting how a range of similar genetic and environmental factors are associated with both cognitive function and schizophrenia. We then review the pathophysiological mechanisms thought to underlie cognitive symptoms, including the role of dopamine, cholinergic signalling and the balance between GABAergic interneurons and glutamatergic pyramidal cells. Finally, we review the clinical management of cognitive impairments and candidate novel treatments.

N-acetylcysteine treatment mitigates loss of cortical parvalbumin-positive interneuron and perineuronal net integrity resulting from persistent oxidative stress in a rat TBI model

Traumatic brain injury (TBI) increases cerebral reactive oxygen species production, which leads to continuing secondary neuronal injury after the initial insult. Cortical parvalbumin-positive interneurons (PVIs; neurons responsible for maintaining cortical inhibitory tone) are particularly vulnerable to oxidative stress and are thus disproportionately affected by TBI. Systemic N-acetylcysteine (NAC) treatment may restore cerebral glutathione equilibrium, thus preventing post-traumatic cortical PVI loss. We therefore tested whether weeks-long post-traumatic NAC treatment mitigates cortical oxidative stress, and whether such treatment preserves PVI counts and related markers of PVI integrity and prevents pathologic electroencephalographic (EEG) changes, 3 and 6 weeks after fluid percussion injury in rats. We find that moderate TBI results in persistent oxidative stress for at least 6 weeks after injury and leads to the loss of PVIs and the perineuronal net (PNN) that surrounds them as well as of per-cell parvalbumin expression. Prolonged post-TBI NAC treatment normalizes the cortical redox state, mitigates PVI and PNN loss, and - in surviving PVIs - increases per-cell parvalbumin expression. NAC treatment also preserves normal spectral EEG measures after TBI. We cautiously conclude that weeks-long NAC treatment after TBI may be a practical and well-tolerated treatment strategy to preserve cortical inhibitory tone post-TBI.

Physical exercise modulates the microglial complement pathway in mice to relieve cortical circuitry deficits induced by mutant human TDP-43

The aggregation of TAR DNA binding protein 43 kDa (TDP-43) is related to different neurodegenerative diseases, which leads to microglial activation and neuronal loss. The molecular mechanism driving neuronal death by reactive microglia, however, has not been completely resolved. In this study, we generated a mouse model by overexpressing mutant human TDP-43 (M337V) in the primary motor cortex, leading to prominent motor-learning deficits. In vivo 2-photon imaging shows an active approach of microglia toward parvalbumin interneurons, resulting in disrupted cortical excitatory-inhibitory balance. Proteomics studies suggest that activation of the complement pathway induces microglial activity. To develop an early interventional strategy, treadmill exercise successfully prevents the deterioration of motor dysfunction under enhanced adipocytic release of clusterin to block the complement pathway. These results demonstrate a previously unrecognized pathway by which TDP-43 induces cortical deficits and provide additional insights for the mechanistic explanation of exercise training in disease intervention.

Cell-specific vulnerability to metabolic failure: the crucial role of parvalbumin expressing neurons in creatine transporter deficiency

Mutations in the solute carrier family 6-member 8 (Slc6a8) gene, encoding the protein responsible for cellular creatine (Cr) uptake, cause Creatine Transporter Deficiency (CTD), an X-linked neurometabolic disorder presenting with intellectual disability, autistic-like features, and epilepsy. The pathological determinants of CTD are still poorly understood, hindering the development of therapies. In this study, we generated an extensive transcriptomic profile of CTD showing that Cr deficiency causes perturbations of gene expression in excitatory neurons, inhibitory cells, and oligodendrocytes which result in remodeling of circuit excitability and synaptic wiring. We also identified specific alterations of parvalbumin-expressing (PV⁺) interneurons, exhibiting a reduction in cellular and synaptic density, and a hypofunctional electrophysiological phenotype. Mice lacking Slc6a8 only in PV⁺ interneurons recapitulated numerous CTD features, including cognitive deterioration, impaired cortical processing and hyperexcitability of brain circuits, demonstrating that Cr deficit in PV⁺ interneurons is sufficient to determine the neurological phenotype of CTD. Moreover, a pharmacological treatment targeted to restore the efficiency of PV⁺ synapses significantly improved cortical activity in Slc6a8 knock-out animals. Altogether, these data demonstrate that Slc6a8 is critical for the normal function of PV⁺ interneurons and that impairment of these cells is central in the disease pathogenesis, suggesting a novel therapeutic venue for CTD.

Shank3a/b isoforms regulate the susceptibility to seizures and thalamocortical development in the early postnatal period of mice

Epileptic seizures are distinct but frequent comorbidities in children with autism spectrum disorder (ASD). The hyperexcitability of cortical and subcortical neurons appears to be involved in both phenotypes. However, little information is available concerning which genes are involved and how they regulate the excitability of the thalamocortical network. In this study, we investigate whether an ASD-associated gene, SH3 and multiple ankyrin repeat domains 3 (Shank3), plays a unique role in the postnatal development of thalamocortical neurons. We herein report that Shank3a/b, the splicing isoforms of mouse Shank3, were uniquely expressed in the thalamic nuclei, peaking from two to four weeks after birth. Shank3a/b-knockout mice showed lower parvalbumin signals in the thalamic nuclei. Consistently, Shank3a/b-knockout mice were more susceptible to generalized seizures than wild-type mice after kainic acid treatments. Together, these data indicate that NT-Ank domain of Shank3a/b regulates molecular pathways that protect thalamocortical neurons from hyperexcitability during the early postnatal period of mice.

Prepubertal ovariectomy confers resilience to stress-induced anxiety in adult female mice

The increased vulnerability to stress-induced neuropsychiatric disorders in women, including anxiety disorders, does not emerge until pubertal onset, suggesting a role for ovarian hormones in organizing sex-specific vulnerability to anxiety. Parvalbumin (PV) interneurons in the prefrontal cortex are a potential target for these ovarian hormones. PV+ interneurons undergo maturation during the adolescent period and have been shown to be sensitive to stress and to mediate stress-induced anxiety in female mice. To test the idea that ovarian hormones at puberty are necessary for the acquisition of sensitivity to stress, hypothetically driving the response of PV+ interneurons to stress, we performed ovariectomy or sham surgery before pubertal onset in female mice. These mice then were exposed to four weeks of unpredictable chronic mild stress in adulthood. We then assessed anxiety-like behavior and PV/FosB colocalization in the medial PFC. Additionally, we assessed stress-induced anxiety-like behavior in female mice following ovariectomy in adulthood to determine if puberty is a sensitive period for ovarian hormones in mediating vulnerability to stress. We found that prepubertal ovariectomy protects against the development of anxiety-like behavior in adulthood, an effect not found following ovariectomy in adulthood. This effect may be independent of ovarian hormones on prefrontal PV+ interneurons response to stress.

Retinoic Acid Prevents the Neuronal Damage Through the Regulation of Parvalbumin in an Ischemic Stroke Model

Ischemic stroke is a neurological disease that causes brain damage by increasing oxidative stress and ion imbalance. Retinoic acid is a major metabolite of vitamin A and regulates oxidative stress, calcium homeostasis, and cell death. Intracellular calcium is involved in neuronal growth and synaptic plasticity. Parvalbumin is a calcium-binding protein that is mainly expressed in brain. In this study, we investigated whether retinoic acid has neuroprotective effects by controlling intracellular calcium concentration and parvalbumin expression in ischemic brain damage. Middle cerebral artery occlusion (MCAO) was performed to induce cerebral ischemia. Retinoic acid (5 mg/kg) or vehicle was injected into the abdominal cavity for four days before surgery and cerebral cortices were collected 24 h after MCAO for further studies. MCAO damage induced neurological deficits and histopathological changes and decreased parvalbumin expression. However, retinoic acid treatment alleviated these changes. In cultured neurons, glutamate (5 mM) exposure induced neuronal cell death, increased intracellular calcium concentration, and decreased parvalbumin expression. Retinoic acid treatment attenuated these changes against glutamate toxicity in a dose-dependent manner. It also regulates glutamate induced change in bcl-2 and bax expression. The mitigation effects of retinoic acid were greater under non-transfection conditions than under parvalbumin siRNA transfection conditions. Our findings showed that retinoic acid modulates intracellular calcium concentration and parvalbumin expression and prevents apoptosis in ischemic brain injury. In conclusion, retinoic acid contributes to the preservation of neurons from ischemic stroke by controlling parvalbumin expression and apoptosis-related proteins.

Linking Social Cognition, Parvalbumin Interneurons, and Oxytocin in Alzheimer's Disease: An Update

Finding a cure for Alzheimer's disease (AD) has been notoriously challenging for many decades. Therefore, the current focus is mainly on prevention, timely intervention, and slowing the progression in the earliest stages. A better understanding of underlying mechanisms at the beginning of the disease could aid in early diagnosis and intervention, including alleviating symptoms or slowing down the disease progression. Changes in social cognition and progressive parvalbumin (PV) interneuron dysfunction are among the earliest observable effects of AD. Various AD rodent models mimic these early alterations, but only a narrow field of study has considered their mutual relationship. In this review, we discuss current knowledge about PV interneuron dysfunction in AD and emphasize their importance in social cognition and memory. Next, we propose oxytocin (OT) as a potent modulator of PV interneurons and as a promising treatment for managing some of the early symptoms. We further discuss the supporting evidence on its beneficial effects on AD-related pathology. Clinical trials have employed the use of OT in various neuropsychiatric diseases with promising results, but little is known about its prospective impacts on AD. On the other hand, the modulatory effects of OT in specific structures and local circuits need to be clarified in future studies. This review highlights the connection between PV interneurons and social cognition impairment in the early stages of AD and considers OT as a promising therapeutic agent for addressing these early deficits.

Maternal separation in mice leads to anxiety-like/aggressive behavior and increases immunoreactivity for glutamic acid decarboxylase and parvalbumin in the adolescence ventral hippocampus

It has been reported that stressful events in early life influence behavior in adulthood and are associated with different psychiatric disorders, such as major depression, post-traumatic stress disorder, bipolar disorder, and anxiety disorder. Maternal separation (MS) is a representative animal model for reproducing childhood stress. It is used as an animal model for depression, and has well-known effects, such as increasing anxiety behavior and causing abnormalities in the hypothalamic-pituitary-adrenal (HPA) axis. This study investigated the effect of MS on anxiety or aggression-like behavior and the number of GABAergic neurons in the hippocampus. Mice were separated from their dams for four hours per day for 19 d from postnatal day two. Elevated plus maze (EPM) test, resident-intruder (RI) test, and counted glutamic acid decarboxylase 67 (GAD67) or parvalbumin (PV) positive cells in the hippocampus were executed using immunohistochemistry. The maternal segregation group exhibited increased anxiety and aggression in the EPM test and the RI test. GAD67-positive neurons were increased in the hippocampal regions we observed: dentate gyrus (DG), CA3, CA1, subiculum, presubiculum, and parasubiculum. PV-positive neurons were increased in the DG, CA3, presubiculum, and parasubiculum. Consistent with behavioral changes, corticosterone was increased in the MS group, suggesting that the behavioral changes induced by MS were expressed through the effect on the HPA axis. Altogether, MS alters anxiety and aggression levels, possibly through alteration of cytoarchitecture and output of the ventral hippocampus that induces the dysfunction of the HPA axis.

Insights into the role of intracellular calcium signaling in the neurobiology of neurodevelopmental disorders

Calcium (Ca²⁺) comprises a critical ionic second messenger in the central nervous system that is under the control of a wide array of regulatory mechanisms, including organellar Ca²⁺ stores, membrane channels and pumps, and intracellular Ca²⁺-binding proteins. Not surprisingly, disturbances in Ca²⁺ homeostasis have been linked to neurodegenerative disorders, such as Alzheimer's and Parkinson's diseases. However, aberrations in Ca²⁺ homeostasis have also been implicated in neuropsychiatric disorders with a strong neurodevelopmental component including autism spectrum disorder (ASD) attention-deficit hyperactivity disorder (ADHD) and schizophrenia (SCZ). While plasma membrane Ca²⁺ channels and synaptic Ca²⁺-binding proteins have been extensively studied, increasing evidence suggests a prominent role for intracellular Ca²⁺ stores, such as the endoplasmic reticulum (ER), in aberrant neurodevelopment. In the context of the current mini-review, we discuss recent findings implicating critical intracellular Ca²⁺-handling regulators such as the sarco-ER Ca²⁺ ATPase 2 (SERCA2), ryanodine receptors (RyRs), inositol triphosphate receptors (IP₃Rs), and parvalbumin (PVALB), in the emergence of ASD, SCZ, and ADHD.

Mature parvalbumin interneuron function in prefrontal cortex requires activity during a postnatal sensitive period

In their seminal findings, Hubel and Wiesel identified sensitive periods in which experience can exert lasting effects on adult visual cortical functioning and behavior via transient changes in neuronal activity during development. Whether comparable sensitive periods exist for non-sensory cortices, such as the prefrontal cortex, in which alterations in activity determine adult circuit function and behavior is still an active area of research. Here, using mice we demonstrate that inhibition of prefrontal parvalbumin (PV)-expressing interneurons during the juvenile and adolescent period, results in persistent impairments in adult prefrontal circuit connectivity, in vivo network function, and behavioral flexibility that can be reversed by targeted activation of PV interneurons in adulthood. In contrast, reversible suppression of PV interneuron activity in adulthood produces no lasting effects. These findings identify an activity-dependent sensitive period for prefrontal circuit maturation and highlight how abnormal PV interneuron activity during development alters adult prefrontal circuit function and cognitive behavior.

Cognitively impaired aged Octodon degus recapitulate major neuropathological features of sporadic Alzheimer's disease

The long-lived Chilean rodent (Octodon degus) has been reported to show spontaneous age-dependent neuropathology and cognitive impairments similar to those observed in human AD. However, the handful of published papers on degus of differing genetic backgrounds yield inconsistent findings about sporadic AD-like pathological features, with notably differing results between lab in-bred degus versus outbred degus. This motivates more extensive characterization of spontaneously occurring AD-like pathology and behavior in degus. In the present study, we show AD-like neuropathological markers in the form of amyloid deposits and tau abnormalities in a cognitively impaired subset of aged outbred degus. Compared to the aged degus that show normal burrowing behavior, the age-matched degus with burrowing behavior deficits correlatively exhibit detectable human AD-like Aβ deposits and tau neuropathology, along with neuroinflammatory markers that include enhanced microglial activation and higher numbers of reactive astrocytes in the brain. This subset of cognitively impaired aged degus also exhibits cerebral amyloid angiopathy and tauopathy. We find robust neurodegenerative features in behaviorally deficient aged degus, including hippocampal neuronal loss, altered parvalbumin and perineuronal net staining in the cortex, and increased c-Fos neuronal activation in the cortex that is consistent with the neural circuit hyperactivity reported in human AD patients. By focusing on the subset of aged degus that show AD-like behavioral deficits and correlative neuropathology, our findings establish outbred degus as a natural model of sporadic AD and demonstrate the potential importance of wild-type outbred genetic backgrounds for AD pathogenesis.

The fate of interneurons, GABAA receptor sub-types and perineuronal nets in Alzheimer's disease

Alzheimer's disease (AD) is the most common neurological disease, which is associated with gradual memory loss and correlated with synaptic hyperactivity and abnormal oscillatory rhythmic brain activity that precedes phenotypic alterations and is partly responsible for the spread of the disease pathology. Synaptic hyperactivity is thought to be because of alteration in the homeostasis of phasic and tonic synaptic inhibition, which is orchestrated by the GABA_A inhibitory system, encompassing subclasses of interneurons and GABA_A receptors, which play a vital role in cognitive functions, including learning and memory. Furthermore, the extracellular matrix, the perineuronal nets (PNNs) which often go unnoticed in considerations of AD pathology, encapsulate the inhibitory cells and neurites in critical brain regions and have recently come under the light for their crucial role in synaptic stabilisation and excitatory-inhibitory balance and when disrupted, serve as a potential trigger for AD-associated synaptic imbalance. Therefore, in this review, we summarise the current understanding of the selective vulnerability of distinct interneuron subtypes, their synaptic and extrasynaptic GABA_A R subtypes as well as the changes in PNNs in AD, detailing their contribution to the mechanisms of disease development. We aim to highlight how seemingly unique malfunction in each component of the interneuronal GABA inhibitory system can be tied together to result in critical circuit dysfunction, leading to the irreversible symptomatic damage observed in AD.

Isoflurane Rescue Schizophrenia-Related Deficits through Parvalbumin-Positive Neurons in the Dentate Gyrus

The therapeutic effects of volatile anesthetics on mental diseases, particularly schizophrenia, have gained considerable interest. Although isoflurane is a commonly used volatile anesthetic, there’s no more evidence that it could work on treating schizophrenia. Here, we discovered that inhaling isoflurane at low concentrations might reverse the behavioral phenotypes of schizophrenia caused by MK801, such as hyperlocomotion, pre-pulse inhibition impairment, and working memory loss. Isoflurane also helped recovering adult neurogenesis and synaptic plasticity impairments in the dentate gyrus (DG) induced by MK801. To better understand the mechanism, we discovered that isoflurane could reverse the reduction of parvalbumin (PV)-positive GABAergic interneuron (PVI) number and the aberration of NRG1-ErbB4 signaling in the DG; however, isoflurane could not reverse the schizophrenia-related phenotypes caused by PVI ablation, indicating that PVI are necessary for the therapeutic effect of isoflurane. Interestingly, isoflurane could reverse phenotypes caused by blocking PVIs GABA release in the DG, indicating the therapeutic impact is independent of PVI GABA release. Our research revealed that isoflurane might be used to treat schizophrenia, possibly through PVI in the DG.

Parvalbumin interneuron-derived tissue-type plasminogen activator shapes perineuronal net structure

Background

Perineuronal nets (PNNs) are specialized extracellular matrix structures mainly found around fast-spiking parvalbumin (FS-PV) interneurons. In the adult, their degradation alters FS-PV-driven functions, such as brain plasticity and memory, and altered PNN structures have been found in neurodevelopmental and central nervous system disorders such as Alzheimer’s disease, leading to interest in identifying targets able to modify or participate in PNN metabolism. The serine protease tissue-type plasminogen activator (tPA) plays multifaceted roles in brain pathophysiology. However, its cellular expression profile in the brain remains unclear and a possible role in matrix plasticity through PNN remodeling has never been investigated.

Result

By combining a GFP reporter approach, immunohistology, electrophysiology, and single-cell RT-PCR, we discovered that cortical FS-PV interneurons are a source of tPA in vivo. We found that mice specifically lacking tPA in FS-PV interneurons display denser PNNs in the somatosensory cortex, suggesting a role for tPA from FS-PV interneurons in PNN remodeling. In vitro analyses in primary cultures of mouse interneurons also showed that tPA converts plasminogen into active plasmin, which in turn, directly degrades aggrecan, a major structural chondroitin sulfate proteoglycan (CSPG) in PNNs.

Conclusions

We demonstrate that tPA released from FS-PV interneurons in the central nervous system reduces PNN density through CSPG degradation. The discovery of this tPA-dependent PNN remodeling opens interesting insights into the control of brain plasticity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01419-8.

Dysregulation of prefrontal parvalbumin interneurons leads to adult aggression induced by social isolation stress during adolescence

Social isolation during the juvenile stage results in structural and functional impairment of the brain and deviant adult aggression. However, the specific subregions and cell types that underpin this deviant behavior are still largely unknown. Here, we found that adolescent social isolation led to a shortened latency to attack onset and extended the average attack time, accompanied by anxiety-like behavior and deficits in social preference in adult mice. However, when exposed to social isolation during adulthood, the mice did not show these phenotypes. We also found that the structural plasticity of prefrontal pyramidal neurons, including the dendritic complexity and spine ratio, was impaired in mice exposed to adolescent social isolation. The parvalbumin (PV) interneurons in the prefrontal infralimbic cortex (IL) are highly vulnerable to juvenile social isolation and exhibit decreased cell numbers and reduced activation in adulthood. Moreover, chemogenetic inactivation of IL-PV interneurons can mimic juvenile social isolation-induced deviant aggression and social preference. Conversely, artificial activation of IL-PV interneurons significantly attenuated deviant aggression and rescued social preference during adulthood in mice exposed to adolescent social isolation. These findings implicate juvenile social isolation-induced damage to IL-PV interneurons in long-term aggressive behavior in adulthood.

Learning from inhibition: Functional roles of hippocampal CA1 inhibition in spatial learning and memory

Hippocampal inhibitory interneurons exert a powerful influence on learning and memory. Inhibitory interneurons are known to play a major role in many diseases that affect memory, and to strongly influence brain functions required for memory-related tasks. While previous studies involving genetic, optogenetic, and pharmacological manipulations have shown that hippocampal interneurons play essential roles in spatial and episodic learning and memory, exactly how interneurons affect local circuit computations during spatial navigation is not well understood. Given the significant anatomical, morphological, and functional heterogeneity in hippocampal interneurons, one may suspect cell-type specific roles in circuit computations. Here, we review emerging evidence of CA1 hippocampal interneurons' role in local circuit computations that support spatial learning and memory and discuss open questions about CA1 interneurons in spatial learning.

Repeated methamphetamine administration produces cognitive deficits through augmentation of GABAergic synaptic transmission in the prefrontal cortex

Methamphetamine (METH) abuse is associated with the emergence of cognitive deficits and hypofrontality, a pathophysiological marker of many neuropsychiatric disorders that is produced by altered balance of local excitatory and inhibitory synaptic transmission. However, there is a dearth of information regarding the cellular and synaptic mechanisms underlying METH-induced cognitive deficits and associated hypofrontal states. Using PV-Cre transgenic rats that went through a METH sensitization regime or saline (SAL) followed by 7-10 days of home cage abstinence combined with cognitive tests, chemogenetic experiments, and whole-cell patch recordings on the prelimbic prefrontal cortex (PFC), we investigated the cellular and synaptic mechanisms underlying METH-induce hypofrontality. We report here that repeated METH administration in rats produces deficits in working memory and increases in inhibitory synaptic transmission onto pyramidal neurons in the PFC. The increased PFC inhibition is detected by an increase in spontaneous and evoked inhibitory postsynaptic synaptic currents (IPSCs), an increase in GABAergic presynaptic function, and a shift in the excitatory-inhibitory balance onto PFC deep-layer pyramidal neurons. We find that pharmacological blockade of D1 dopamine receptor function reduces the METH-induced augmentation of IPSCs, suggesting a critical role for D1 dopamine signaling in METH-induced hypofrontality. In addition, repeated METH administration increases the intrinsic excitability of parvalbumin-positive fast spiking interneurons (PV + FSIs), a key local interneuron population in PFC that contributes to the control of inhibitory tone. Using a cell type-specific chemogenetic approach, we show that increasing PV + FSIs activity in the PFC is necessary and sufficient to cause deficits in temporal order memory similar to those induced by METH. Conversely, reducing PV + FSIs activity in the PFC of METH-exposed rats rescues METH-induced temporal order memory deficits. Together, our findings reveal that repeated METH exposure increases PFC inhibitory tone through a D1 dopamine signaling-dependent potentiation of inhibitory synaptic transmission, and that reduction of PV + FSIs activity can rescue METH-induced cognitive deficits, suggesting a potential therapeutic approach to treating cognitive symptoms in patients suffering from METH use disorder.

Proteome-Wide Analysis of the Hippocampus in Adult Mice with Learning and Memory Impairment Caused by Chronic Ethanol Exposure

Alcohol consumption may cause various impairments in the brain. The hippocampus is particularly vulnerable to alcohol exposure, which may cause learning and memory deficits. Recently, proteomics analysis has become a popular approach to explore the pathogenesis of various diseases. The present study was conducted to investigate protein expression alteration in the hippocampus and to identify the molecular mechanisms underlying ethanol-induced learning and memory impairments. Mouse models of chronic ethanol intoxication were established by intragastrical administration for 28 consecutive days, and hippocampal neuronal damage was assessed by Nissl staining. Recognition memory was evaluated by Novel object recognition and Morris water maze tests, and hippocampus tissues were collected for label-free quantitative proteomics and analyzed using bioinformatics methods. Our study showed that chronic ethanol exposure prompted marked changes in protein expression in the hippocampus. We identified 32 differentially expressed proteins, of which 21 were upregulated and 11 downregulated. Gene Ontology analysis suggested that the identified differentially proteins were mainly involved in cytoskeleton and signal transduction mechanisms. Further verification using Western blotting and real-time quantitative PCR revealed that the hippocampal CTSL (cathepsin L), and PVALB (Parvalbumin) showed strongest expression changes, the latter being specifically expressed in GABAergic interneurons. These two proteins might serve as candidate protein biomarkers, providing new prospects for the diagnosis and treatment of ethanol-induced learning and memory disorders.