Inhibition of parvalbumin-expressing interneurons results in complex behavioral changes

Thienopyrimidinone Derivatives as a GluN2B/C/D Biased, Positive Allosteric Modulator of the N-Methyl-d-Aspartate Receptor

Positive allosteric modulators (PAMs) of the N-methyl-d-aspartate receptor (NMDAR) have been proposed as therapeutics in several neuropsychiatric indications, including schizophrenia, depression, cognitive dysfunction, and anxiety. In particular, GluN2D-containing NMDARs are highly expressed in inhibitory interneurons and are a target of interest for drug development. Toward that end, we describe our investigation into the GluN2-selective EU 1622 series of PAMs that enhance receptor efficacy, increase agonist potency, prolong deactivation time course, reduce single channel conductance, and limit calcium influx. Through SAR studies of the amide, aryl, and thiophene side chains, we identified analogues with submicromolar potency that preferentially potentiate GluN2B-, GluN2C-, and GluN2D-containing NMDARs. Elaboration of the thiophene side chain to block metabolism resulted in the discovery of EU 1622-240 (25b) with improved metabolic stability, oral bioavailability, and CNS penetration in rodents. Consequently, we present data with EU 1622-240 showing the promising properties of this series as a biased GluN2 potentiator.

Quantifying multilabeled brain cells in the whole prefrontal cortex reveals reduced inhibitory and a subtype of excitatory neuronal marker expression in serotonin transporter knockout rats

The prefrontal cortex regulates emotions and is influenced by serotonin. Rodents lacking the serotonin transporter (5-HTT) show increased anxiety and changes in excitatory and inhibitory cell markers in the prefrontal cortex. However, these observations are constrained by limitations in brain representation and cell segmentation, as standard immunohistochemistry is inadequate to consider volume variations in regions of interest. We utilized the deep learning network of the StarDist method in combination with novel open-source methods for automated cell counts in a wide range of prefrontal cortex subregions. We found that 5-HTT knockout rats displayed increased anxiety and diminished relative numbers of subclass excitatory VGluT2+ and activated ΔFosB+ cells in the infralimbic and prelimbic cortices and of inhibitory GAD67+ cells in the prelimbic cortex. Anxiety levels and ΔFosB cell counts were positively correlated in wild-type, but not in knockout, rats. In conclusion, we present a novel method to quantify whole brain subregions of multilabeled cells in animal models and demonstrate reduced excitatory and inhibitory neuronal marker expression in prefrontal cortex subregions of 5-HTT knockout rats.

Computational Synaptic Modeling of Pitch and Duration Mismatch Negativity in First-Episode Psychosis Reveals Selective Dysfunction of the N-Methyl-D-Aspartate Receptor

Mismatch negativity (MMN) to pitch (pMMN) and to duration (dMMN) deviant stimuli is significantly more attenuated in long-term psychotic illness compared to first-episode psychosis (FEP). It was recently shown that source-modeling of magnetically recorded MMN increases the detection of left auditory cortex MMN deficits in FEP, and that computational circuit modeling of electrically recorded MMN also reveals left-hemisphere auditory cortex abnormalities. Computational modeling using dynamic causal modeling (DCM) can also be used to infer synaptic activity from EEG-based scalp recordings. We measured pMMN and dMMN with EEG from 26 FEP and 26 matched healthy controls (HCs) and used a DCM conductance-based neural mass model including α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid, N-methyl-D-Aspartate (NMDA), and Gamma-aminobutyric acid receptors to identify any changes in effective connectivity and receptor rate constants in FEP. We modeled MMN sources in bilateral A1, superior temporal gyrus, and inferior frontal gyrus (IFG). No model parameters distinguished groups for pMMN. For dMMN, reduced NMDA receptor activity in right IFG in FEP was detected. This finding is in line with literature of prefrontal NMDA receptor hypofunction in chronic schizophrenia and suggests impaired NMDA-induced synaptic plasticity may be present at psychosis onset where scalp dMMN is only moderately reduced. To the best of our knowledge, this is the first report of impaired NMDA receptor activity in FEP found through computational modeling of dMMN and shows the potential of DCM to non-invasively reveal synaptic-level abnormalities that underly subtle functional auditory processing deficits in early psychosis.

Alcohol Withdrawal Alters the Inhibitory Landscape of the Prelimbic Cortex in an Interneuron- and Sex-specific Manner

Alcohol use disorder (AUD) is highly prevalent and associated with substantial morbidity and high mortality among substance use disorders. While there are currently three FDA-approved medications for treating AUDs, none specifically target the withdrawal/negative affect stage of AUD, underscoring the need to understand the underlying neurobiology during this critical stage of the addiction cycle. One key region involved in alcohol withdrawal and negative affect is the prelimbic cortex, a subregion of the medial prefrontal cortex. While previous studies have examined alcohol-related adaptations in prefrontal cortical principal glutamatergic neurons, here we used male and female PV:Ai14, SOM:Ai14 and VIP:Ai14 mice to examine synaptic adaptations in all three major classes of prelimbic cortex interneurons following 72 hour withdrawal from a continuous access to two bottle choice model of EtOH drinking in male and female mice. We found that alcohol withdrawal increased excitability of prelimbic PV interneurons in males, but decreased excitability in prelimbic VIP interneurons in females. Additionally, alcohol withdrawal reduced GABA release onto PV interneurons in males while increasing glutamate release onto VIP interneurons in females. In SOM interneurons, alcohol withdrawal had no effect on excitability, but decreased glutamate release onto SOM interneurons in males. Together, our studies identified sex-specific alcohol withdrawal-induced synaptic plasticity in three different types of interneurons and could provide insight into the cellular substrates of negative affective states associated with alcohol withdrawal.

Schizophrenia-Like Deficits and Impaired Glutamate/Gamma-aminobutyric acid Homeostasis in Zfp804a Conditional Knockout Mice

BACKGROUND AND HYPOTHESIS

Zinc finger protein 804A (ZNF804A) was the first genome-wide associated susceptibility gene for schizophrenia (SCZ) and played an essential role in the pathophysiology of SCZ by influencing neurodevelopment regulation, neurite outgrowth, synaptic plasticity, and RNA translational control; however, the exact molecular mechanism remains unclear.

STUDY DESIGN

A nervous-system-specific Zfp804a (ZNF804A murine gene) conditional knockout (cKO) mouse model was generated using clustered regularly interspaced short palindromic repeat/Cas9 technology and the Cre/loxP method.

RESULTS

Multiple and complex SCZ-like behaviors, such as anxiety, depression, and impaired cognition, were observed in Zfp804a cKO mice. Molecular biological methods and targeted metabolomics assay validated that Zfp804a cKO mice displayed altered SATB2 (a cortical superficial neuron marker) expression in the cortex; aberrant NeuN, cleaved caspase 3, and DLG4 (markers of mature neurons, apoptosis, and postsynapse, respectively) expressions in the hippocampus and a loss of glutamate (Glu)/γ-aminobutyric acid (GABA) homeostasis with abnormal GAD67 (Gad1) expression in the hippocampus. Clozapine partly ameliorated some SCZ-like behaviors, reversed the disequilibrium of the Glu/GABA ratio, and recovered the expression of GAD67 in cKO mice.

CONCLUSIONS

Zfp804a cKO mice reproducing SCZ-like pathological and behavioral phenotypes were successfully developed. A novel mechanism was determined in which Zfp804a caused Glu/GABA imbalance and reduced GAD67 expression, which was partly recovered by clozapine treatment. These findings underscore the role of altered gene expression in understanding the pathogenesis of SCZ and provide a reliable SCZ model for future therapeutic interventions and biomarker discovery.

Sex-Specific Impacts of Early Life Sleep Disruption: Ethanol Seeking, Social Interaction, and Anxiety Are Differentially Altered in Adolescent Prairie Voles

Early life sleep is important for neuronal development. Using the highly social prairie vole rodent model, we have previously reported that early life sleep disruption (ELSD) during the preweaning period results in interference with social bonding and increases ethanol consumption following a stressor in adulthood. Furthermore, ELSD increases parvalbumin expression and reduces glutamatergic neurotransmission in cortical regions in adult prairie voles. To understand the impact of ELSD on the lifespan, an examination of an earlier time in life is necessary. The aim of the present study was to examine behavioral outcomes of ELSD on adolescent prairie voles. Given the known effects of ELSD on development of neuronal systems involved in mood and social motivation, we hypothesized that anxiety, risk, and reward-related behaviors would be impacted by ELSD in adolescent prairie voles. We report that both male and female adolescent prairie voles that experienced ELSD showed heightened anxiety-like behavior compared to age-matched controls (CONs) as measured by a light-dark box. Additionally, both male and female ELSD voles showed reductions in both ethanol preference and consumption, and affiliative behavior compared to CONs. These results suggest that adolescent prairie voles of both sexes experience heightened anxiety-like behavior and reduced reward-seeking behaviors after ELSD. These results further suggest that early life sleep is critically important for neurotypical behaviors in adolescence.

Timed fetal inflammation and postnatal hypoxia cause cortical white matter injury, interneuron imbalances, and behavioral deficits in a double-hit rat model of encephalopathy of prematurity

Extreme preterm birth-associated adversities are a major risk factor for aberrant brain development, known as encephalopathy of prematurity (EoP), which can lead to long-term neurodevelopmental impairments. Although progress in clinical care for preterm infants has markedly improved perinatal outcomes, there are currently no curative treatment options available to combat EoP. EoP has a multifactorial etiology, including but not limited to pre- or postnatal immune activation and oxygen fluctuations. Elucidating the underlying mechanisms of EoP and determining the efficacy of potential therapies relies on valid, clinically translatable experimental models that reflect the neurodevelopmental and pathophysiological hallmarks of EoP. Here, we expand on our double-hit rat model that can be used to study EoP disease mechanisms and therapeutic options in a preclinical setting. Pregnant Wistar dams were intraperitoneally injected with 10 μg/kg LPS on embryonic day (E)20 and offspring was subjected to hypoxia (140 min, 8% O2) at postnatal day 4. Rats exposed to fetal inflammation and postnatal hypoxia (FIPH) showed neurodevelopmental impairments, such as reduced nest-seeking ability, ultrasonic vocalizations, social engagement, and working memory, and increased anxiety and sensitivity. Impairments in myelination, oligodendrocyte maturation and interneuron development were examined as hallmarks for EoP, in different layers and coordinates of the cortex using histological and molecular techniques. Myelin density and complexity was decreased in the cortex, which partially coincided with a decrease in mature oligodendrocytes. Furthermore, interneuron populations (GAD67+ and PVALB+) were affected. To determine if the timing of inducing fetal inflammation affected the severity of EoP hallmarks in the cortex, multiple timepoints of fetal inflammation were compared. Inflammation at E20 combined with postnatal hypoxia gave the most severe EoP phenotype in the cortex. In conclusion, we present a double-hit rat model which displays various behavioral, anatomical and molecular hallmarks of EoP, including diffuse white matter injury. This double-hit model can be used to investigate pathophysiological mechanisms and potential therapies for EoP.

GABAergic dysfunction in postmortem dorsolateral prefrontal cortex: implications for cognitive deficits in schizophrenia and affective disorders

The microcircuitry within superficial layers of the dorsolateral prefrontal cortex (DLPFC), composed of excitatory pyramidal neurons and inhibitory GABAergic interneurons, has been suggested as the neural substrate of working memory performance. In schizophrenia, working memory impairments are thought to result from alterations of microcircuitry within the DLPFC. GABAergic interneurons, in particular, are crucially involved in synchronizing neural activity at gamma frequency, the power of which increases with working memory load. Alterations of GABAergic interneurons, particularly parvalbumin (PV) and somatostatin (SST) subtypes, are frequently observed in schizophrenia. Abnormalities of GABAergic neurotransmission, such as deficiencies in the 67 kDA isoform of GABA synthesis enzyme (GAD67), vesicular GABA transporter (vGAT), and GABA reuptake transporter 1 (GAT1) in presynaptic boutons, as well as postsynaptic alterations in GABA A receptor subunits further contribute to impaired inhibition. This review explores GABAergic abnormalities of the postmortem DLPFC in schizophrenia, with a focus on the roles of interneuron subtypes involved in cognition, and GABAergic neurotransmission within presynaptic boutons and postsynaptic alterations. Where available, comparisons between schizophrenia and affective disorders that share cognitive pathology such as bipolar disorder and major depressive disorder will be made. Challenges in directly measuring GABA levels are addressed, emphasizing the need for innovative techniques. Understanding GABAergic abnormalities and their implications for neural circuit dysfunction in schizophrenia is crucial for developing targeted therapies.

Intracellular spatial transcriptomic analysis toolkit (InSTAnT)

Imaging-based spatial transcriptomics technologies such as Multiplexed error-robust fluorescence in situ hybridization (MERFISH) can capture cellular processes in unparalleled detail. However, rigorous and robust analytical tools are needed to unlock their full potential for discovering subcellular biological patterns. We present Intracellular Spatial Transcriptomic Analysis Toolkit (InSTAnT), a computational toolkit for extracting molecular relationships from spatial transcriptomics data at single molecule resolution. InSTAnT employs specialized statistical tests and algorithms to detect gene pairs and modules exhibiting intriguing patterns of co-localization, both within individual cells and across the cellular landscape. We showcase the toolkit on five different datasets representing two different cell lines, two brain structures, two species, and three different technologies. We perform rigorous statistical assessment of discovered co-localization patterns, find supporting evidence from databases and RNA interactions, and identify associated subcellular domains. We uncover several cell type and region-specific gene co-localizations within the brain. Intra-cellular spatial patterns discovered by InSTAnT mirror diverse molecular relationships, including RNA interactions and shared sub-cellular localization or function, providing a rich compendium of testable hypotheses regarding molecular functions.

Serine racemase deletion alters adolescent social behavior and whole-brain cFos activation

Background

Neurodevelopmental disorders (NDDs) can cause debilitating impairments in social cognition and aberrant functional connectivity in large-scale brain networks, leading to social isolation and diminished everyday functioning. To facilitate the treatment of social impairments, animal models of NDDs that link N- methyl-D-aspartate receptor (NMDAR) hypofunction to social deficits in adulthood have been used. However, understanding the etiology of social impairments in NDDs requires investigating social changes during sensitive windows during development.

Methods

We examine social behavior during adolescence using a translational mouse model of NMDAR hypofunction (SR-/-) caused by knocking out serine racemase (SR), the enzyme needed to make D-serine, a key NMDAR coagonist. Species-typical social interactions are maintained through brain-wide neural activation patterns; therefore, we employed whole-brain cFos activity mapping to examine network-level connectivity changes caused by SR deletion.

Results

In adolescent SR-/- mice, we observed disinhibited social behavior toward a novel conspecific and rapid social habituation toward familiar social partners. SR-/- mice also spent more time in the open arm of the elevated plus maze which classically points to an anxiolytic behavioral phenotype. These behavioral findings point to a generalized reduction in anxiety-like behavior in both social and non-social contexts in SR-/- mice; importantly, these findings were not associated with diminished working memory. Inter-regional patterns of cFos activation revealed greater connectivity and network density in SR-/- mice compared to controls.

Discussion

These results suggest that NMDAR hypofunction - a potential biomarker for NDDs - can lead to generalized behavioral disinhibition in adolescence, potentially arising from disrupted communication between and within salience and default mode networks.

Pyramidal and parvalbumin neurons modulate the process of electroacupuncture stimulation for stroke rehabilitation

Electroacupuncture (EA) stimulation has been shown to be beneficial in stroke rehabilitation; however, little is known about the neurological mechanism by which this peripheral stimulation approach treats for stroke. This study showed that both pyramidal and parvalbumin (PV) neuronal activity increased in the contralesional primary motor cortex forelimb motor area (M1FL) after ischemic stroke induced by focal unilateral occlusion in the M1FL. EA stimulation reduced pyramidal neuronal activity and increased PV neuronal activity. These results were obtained by a combination of fiber photometry recordings, in vivo and in vitro electrophysiological recordings, and immunofluorescence. Moreover, EA was found to regulate the expression/function of N-methyl-D-aspartate receptors (NMDARs) altered by stroke pathology. In summary, our findings suggest that EA could restore disturbed neuronal activity through the regulation of the activity of pyramidal and PV neurons. Furthermore, NMDARs we shown to play an important role in EA-mediated improvements in sensorimotor ability during stroke rehabilitation.

Gamma Oscillations and Potassium Channel Modulation in Schizophrenia: Targeting GABAergic Dysfunction

Impairments in gamma-aminobutyric acid (GABAergic) interneuron function lead to gamma power abnormalities and are thought to underlie symptoms in people with schizophrenia. Voltage-gated potassium 3.1 (Kv3.1) and 3.2 (Kv3.2) channels on GABAergic interneurons are critical to the generation of gamma oscillations suggesting that targeting Kv3.1/3.2 could augment GABAergic function and modulate gamma oscillation generation. Here, we studied the effect of a novel potassium Kv3.1/3.2 channel modulator, AUT00206, on resting state frontal gamma power in people with schizophrenia. We found a significant positive correlation between frontal resting gamma (35-45 Hz) power (n = 22, r = 0.613, P < .002) and positive and negative syndrome scale (PANSS) positive symptom severity. We also found a significant reduction in frontal gamma power (t13 = 3.635, P = .003) from baseline in patients who received AUT00206. This provides initial evidence that the Kv3.1/3.2 potassium channel modulator, AUT00206, may address gamma oscillation abnormalities in schizophrenia.

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.

Temperament Traits in Pediatric Obsessive-Compulsive Disorder in Relation to Tourette Syndrome and Attention-Deficit Hyperactivity Disorder

INTRODUCTION

Pediatric obsessive-compulsive disorder (OCD), attention-deficit hyperactivity disorder (ADHD), and Tourette syndrome (TS) are often concurrent. This study explores the temperament profile of complex OCD phenotypes.

METHODS

A clinical registry recorded demographic data, psychiatric diagnoses, and temperament traits, including novelty seeking (exploratory behaviors), harm avoidance (fear of uncertainty), reward dependence (sentimentality), and persistence (perseverance). Temperament data were accrued from the Junior Temperament and Character Inventory (JTCI). Participants were divided into (1) OCD only; (2) OCD+ADHD or TS; and (3) OCD+ADHD+TS to compare temperament.

RESULTS

Participants include 126 youths with OCD (61.9% male, 88.9% white) between the ages 6 and 18 years (12.7 ± 3.1). Among the three groups, the complex neurodevelopmental disorder group OCD+ADHD+TS expresses the highest novelty seeking and lowest persistence. Harm avoidance is increased in all groups compared to reference controls, irrespective of concurrent ADHD or TS. For the OCD+ADHD+TS group, contamination and washing symptoms have higher novelty seeking (p < 0.01), while counting and ordering have lower novelty seeking (p < 0.05). Harm avoidance is increased with aggressive, somatic, and checking symptoms in OCD only (p < 0.01), while persistence is increased with repeating and counting symptoms in the comorbid groups (OCD+ADHD or TS, OCD+ADHD+TS).

DISCUSSION/CONCLUSION

The complex subtype, OCD+ADHD+TS, is associated with high novelty seeking and low persistence, while high harm avoidance is linked to pediatric OCD irrespective of ADHD or TS co-occurrence. In sum, pediatric OCD with ADHD and TS confers a unique temperament profile, further refining complex phenotypes of pediatric OCD for future research.

16p11.2 deletion mice exhibit compromised fronto-temporal connectivity, GABAergic dysfunction, and enhanced attentional ability

Autism spectrum disorders are more common in males, and have a substantial genetic component. Chromosomal 16p11.2 deletions in particular carry strong genetic risk for autism, yet their neurobiological impact is poorly characterised, particularly at the integrated systems level. Here we show that mice reproducing this deletion (16p11.2 DEL mice) have reduced GABAergic interneuron gene expression (decreased parvalbumin mRNA in orbitofrontal cortex, and male-specific decreases in Gad67 mRNA in parietal and insular cortex and medial septum). Metabolic activity was increased in medial septum, and in its efferent targets: mammillary body and (males only) subiculum. Functional connectivity was altered between orbitofrontal, insular and auditory cortex, and between septum and hippocampus/subiculum. Consistent with this circuit dysfunction, 16p11.2 DEL mice showed reduced prepulse inhibition, but enhanced performance in the continuous performance test of attentional ability. Level 1 autistic individuals show similarly heightened performance in the equivalent human test, also associated with parietal, insular-orbitofrontal and septo-subicular dysfunction. The data implicate cortical and septal GABAergic dysfunction, and resulting connectivity changes, as the cause of pre-attentional and attentional changes in autism.

microRNA-dependent regulation of gene expression in GABAergic interneurons

Information processing within neuronal circuits relies on their proper development and a balanced interplay between principal and local inhibitory interneurons within those circuits. Gamma-aminobutyric acid (GABA)ergic inhibitory interneurons are a remarkably heterogeneous population, comprising subclasses based on their morphological, electrophysiological, and molecular features, with differential connectivity and activity patterns. microRNA (miRNA)-dependent post-transcriptional control of gene expression represents an important regulatory mechanism for neuronal development and plasticity. miRNAs are a large group of small non-coding RNAs (21-24 nucleotides) acting as negative regulators of mRNA translation and stability. However, while miRNA-dependent gene regulation in principal neurons has been described heretofore in several studies, an understanding of the role of miRNAs in inhibitory interneurons is only beginning to emerge. Recent research demonstrated that miRNAs are differentially expressed in interneuron subclasses, are vitally important for migration, maturation, and survival of interneurons during embryonic development and are crucial for cognitive function and memory formation. In this review, we discuss recent progress in understanding miRNA-dependent regulation of gene expression in interneuron development and function. We aim to shed light onto mechanisms by which miRNAs in GABAergic interneurons contribute to sculpting neuronal circuits, and how their dysregulation may underlie the emergence of numerous neurodevelopmental and neuropsychiatric disorders.

Beyond the γ-aminobutyric acid hypothesis of schizophrenia

Abnormalities in the γ-aminobutyric acid (GABA) system have been reported in the postmortem brains of individuals with schizophrenia. In particular, the reduction of one of the GABA-synthesizing enzymes, the 67-kDa isoform of glutamate decarboxylase (GAD67), has garnered interest among researchers because of its role in the formation of γ-oscillations and its potential involvement in the cognitive dysfunction observed in schizophrenia. Although several animal models have been generated to simulate the alterations observed in postmortem brain studies, they exhibit inconsistent behavioral phenotypes, leading to conflicting views regarding their contributions to the pathogenesis and manifestation of schizophrenia symptoms. For instance, GAD67 knockout rats (also known as Gad1 knockout rats) exhibit marked impairments in spatial working memory, but other model animals do not. In this review, we summarize the phenotypic attributes of these animal models and contemplate the potential for secondary modifications that may arise from the disruption of the GABAergic nervous system.

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.

Targeting parvalbumin promotes M2 macrophage polarization and energy expenditure in mice

Exercise benefits M2 macrophage polarization, energy homeostasis and protects against obesity partially through exercise-induced circulating factors. Here, by unbiased quantitative proteomics on serum samples from sedentary and exercised mice, we identify parvalbumin as a circulating factor suppressed by exercise. Parvalbumin functions as a non-competitive CSF1R antagonist to inhibit M2 macrophage activation and energy expenditure in adipose tissue. More importantly, serum concentrations of parvalbumin positively correlate with obesity in mouse and human, while treating mice with a recombinant parvalbumin blocker prevents its interaction with CSF1R and promotes M2 macrophage polarization and ameliorates diet-induced obesity. Thus, although further studies are required to assess the significance of parvalbumin in mediating the effects of exercise, our results implicate parvalbumin as a potential therapeutic strategy against obesity in mice.

Age- and sex-specific effects of stress on parvalbumin interneurons in preclinical models: Relevance to sex differences in clinical neuropsychiatric and neurodevelopmental disorders

Stress is a major risk factor for neurodevelopmental and neuropsychiatric disorders, with the capacity to impact susceptibility to disease as well as long-term neurobiological and behavioral outcomes. Parvalbumin (PV) interneurons, the most prominent subtype of GABAergic interneurons in the cortex, are uniquely responsive to stress due to their protracted development throughout the highly plastic neonatal period and into puberty and adolescence. Additionally, PV + interneurons appear to respond to stress in a sex-specific manner. This review aims to discuss existing preclinical studies that support our overall hypothesis that the sex-and age-specific impacts of stress on PV + interneurons contribute to differences in individual vulnerability to stress across the lifespan, particularly in regard to sex differences in the diagnostic rate of neurodevelopmental and neuropsychiatric diseases in clinical populations. We also emphasize the importance of studying sex as a biological variable to fully understand the mechanistic and behavioral differences between males and females in models of neuropsychiatric disease.

Sex Differences in Affective Dysfunction and Alterations in Parvalbumin in Rodent Models of Early Life Adversity

The early life environment markedly influences brain and behavioral development, with adverse experiences associated with increased risk of anxiety and depressive phenotypes, particularly in females. Indeed, early life adversity (ELA) in humans (i.e., caregiver deprivation, maltreatment) and rodents (i.e., maternal separation, resource scarcity) is associated with sex-specific emergence of anxious and depressive behaviors. Although these disorders show clear sex differences in humans, little attention has been paid toward evaluating sex as a biological variable in models of affective dysfunction; however, recent rodent work suggests sex-specific effects. Two widely used rodent models of ELA approximate caregiver deprivation (i.e., maternal separation) and resource scarcity (i.e., limited bedding). While these approaches model aspects of ELA experienced in humans, they span different portions of the pre-weaning developmental period and may therefore differentially contribute to underlying mechanistic risk. This is borne out in the literature, where evidence suggests differences in trajectories of behavior depending on the type of ELA and/or sex; however, the neural underpinning of these differences is not well understood. Because anxiety and depression are thought to involve dysregulation in the balance of excitatory and inhibitory signaling in ELA-vulnerable brain regions (e.g., prefrontal cortex, amygdala, hippocampus), outcomes are likely driven by alterations in local and/or circuit-specific inhibitory activity. The most abundant GABAergic subtypes in the brain, accounting for approximately 40% of inhibitory neurons, contain the calcium-binding protein Parvalbumin (PV). As PV-expressing neurons have perisomatic and proximal dendritic targets on pyramidal neurons, they are well-positioned to regulate excitatory/inhibitory balance. Recent evidence suggests that PV outcomes following ELA are sex, age, and region-specific and may be influenced by the type and timing of ELA. Here, we suggest the possibility of a combined role of PV and sex hormones driving differences in behavioral outcomes associated with affective dysfunction following ELA. This review evaluates the literature across models of ELA to characterize neural (PV) and behavioral (anxiety- and depressive-like) outcomes as a function of sex and age. Additionally, we detail a putative mechanistic role of PV on ELA-related outcomes and discuss evidence suggesting hormone influences on PV expression/function which may help to explain sex differences in ELA outcomes.

A Selective Review of the Excitatory-Inhibitory Imbalance in Schizophrenia: Underlying Biology, Genetics, Microcircuits, and Symptoms

Schizophrenia is a chronic disorder characterized by specific positive and negative primary symptoms, social behavior disturbances and cognitive deficits (e.g., impairment in working memory and cognitive flexibility). Mounting evidence suggests that altered excitability and inhibition at the molecular, cellular, circuit and network level might be the basis for the pathophysiology of neurodevelopmental and neuropsychiatric disorders such as schizophrenia. In the past decades, human and animal studies have identified that glutamate and gamma-aminobutyric acid (GABA) neurotransmissions are critically involved in several cognitive progresses, including learning and memory. The purpose of this review is, by analyzing emerging findings relating to the balance of excitatory and inhibitory, ranging from animal models of schizophrenia to clinical studies in patients with early onset, first-episode or chronic schizophrenia, to discuss how the excitatory-inhibitory imbalance may relate to the pathophysiology of disease phenotypes such as cognitive deficits and negative symptoms, and highlight directions for appropriate therapeutic strategies.

Non-cell-autonomous OTX2 transcription factor regulates anxiety-related behavior in the mouse

The OTX2 homeoprotein transcription factor is expressed in the dopaminergic neurons of the ventral tegmental area, which projects to limbic structures controlling complex behaviors. OTX2 is also produced in choroid plexus epithelium, from which it is secreted into cerebrospinal fluid and transferred to limbic structure parvalbumin interneurons. Previously, adult male mice subjected to early-life stress were found susceptible to anxiety-like behaviors, with accompanying OTX2 expression changes in ventral tegmental area or choroid plexus. Here, we investigated the consequences of reduced OTX2 levels in Otx2 heterozygote mice, as well as in Otx2+/AA and scFvOtx2tg/0 mouse models for decreasing OTX2 transfer from choroid plexus to parvalbumin interneurons. Both male and female adult mice show anxiolysis-like phenotypes in all three models. In Otx2 heterozygote mice, we observed no changes in dopaminergic neuron numbers and morphology in ventral tegmental area, nor in their metabolic output and projections to target structures. However, we found reduced expression of parvalbumin in medial prefrontal cortex, which could be rescued in part by adult overexpression of Otx2 specifically in choroid plexus, resulting in increased anxiety-like behavior. Taken together, OTX2 synthesis by the choroid plexus followed by its secretion into the cerebrospinal fluid is an important regulator of anxiety-related phenotypes in the mouse.

Chemogenetic Activation of Cortical Parvalbumin-Positive Interneurons Reverses Noise-Induced Impairments in Gap Detection

Exposure to loud noises not only leads to trauma and loss of output from the ear but also alters downstream central auditory circuits. A perceptual consequence of noise-induced central auditory disruption is impairment in gap-induced prepulse inhibition, also known as gap detection. Recent studies have implicated cortical parvalbumin (PV)-positive inhibitory interneurons in gap detection and prepulse inhibition. Here, we show that exposure to loud noises specifically reduces the density of cortical PV but not somatostatin (SOM)-positive interneurons in the primary auditory cortex in mice (C57BL/6) of both sexes. Optogenetic activation of PV neurons produced less cortical inhibition in noise-exposed than sham-exposed animals, indicative of reduced PV neuron function. Activation of SOM neurons resulted in similar levels of cortical inhibition in noise- and sham-exposed groups. Furthermore, chemogenetic activation of PV neurons with the hM3-based designer receptor exclusively activated by designer drugs completely reversed the impairments in gap detection for noise-exposed animals. These results support the notions that cortical PV neurons encode gap in sound and that PV neuron dysfunction contributes to noise-induced impairment in gap detection.SIGNIFICANCE STATEMENT Noise-induced hearing loss contributes to a range of central auditory processing deficits (CAPDs). The mechanisms underlying noise-induced CAPDs are still poorly understood. Here we show that exposure to loud noises results in dysfunction of PV-positive but not somatostatin-positive inhibitory interneurons in the primary auditory cortex. In addition, cortical PV inhibitory neurons in noise-exposed animals had reduced expression of glutamic acid decarboxylases and weakened inhibition on cortical activity. Noise exposure resulted in impaired gap detection, indicative of disrupted temporal sound processing and possibly tinnitus. We found that chemogenetic activation of cortical PV inhibitory interneurons alleviated the deficits in gap detection. These results implicate PV neuron dysfunction as a mechanism for noise-induced CAPDs.

Elevated expression of complement C4 in the mouse prefrontal cortex causes schizophrenia-associated phenotypes

Accumulating evidence supports immune involvement in the pathogenesis of schizophrenia, a severe psychiatric disorder. In particular, high expression variants of C4, a gene of the innate immune complement system, were shown to confer susceptibility to schizophrenia. However, how elevated C4 expression may impact brain circuits remains largely unknown. We used in utero electroporation to overexpress C4 in the mouse prefrontal cortex. We found reduced glutamatergic input to pyramidal cells of juvenile and adult, but not of newborn C4-overexpressing (C4-OE) mice, together with decreased spine density, which mirrors spine loss observed in the schizophrenic cortex. Using time-lapse two-photon imaging in vivo, we observed that these deficits were associated with decreased dendritic spine gain and elimination in juvenile C4-OE mice, which may reflect poor formation and/or stabilization of immature spines. In juvenile and adult C4-OE mice, we found evidence for NMDA receptor hypofunction, another schizophrenia-associated phenotype, and synaptic accumulation of calcium-permeable AMPA receptors. Alterations in cortical GABAergic networks have been repeatedly associated with schizophrenia. We found that functional GABAergic transmission was reduced in C4-OE mice, in line with diminished GABA release probability from parvalbumin interneurons, lower GAD67 expression, and decreased intrinsic excitability in parvalbumin interneurons. These cellular abnormalities were associated with working memory impairment. Our results substantiate the causal relationship between an immunogenetic risk factor and several distinct cortical endophenotypes of schizophrenia and shed light on the underlying cellular mechanisms.

Weak Association Between the Glutamate Decarboxylase 1 Gene (GAD1) and Schizophrenia in Han Chinese Population

Objectives

Schizophrenia (SZ) is a complex psychiatric disorder with high heritability, and genetic components are thought to be pivotal risk factors for this illness. The glutamate decarboxylase 1 gene (GAD1) was hypothesized to be a candidate risk locus for SZ given its crucial role in the GABAergic neurotransmission system, and previous studies have examined the associations of single nucleotide polymorphisms (SNPs) spanning the GAD1 gene with SZ. However, inconsistent results were obtained. We hence examined the associations between GAD1 SNPs and SZ in two independent case-control samples of Han Chinese ancestry.

Materials and Methods

Two Han Chinese SZ case-control samples, referred as the discovery sample and the replication sample, respectively, were recruited for the current study. The discovery sample comprised of 528 paranoid SZ cases (with age of first onset ≥ 18) and 528 healthy controls; the independent replication sample contained 1,256 early onset SZ cases (with age of first onset < 18) and 2,661 healthy controls. Logistic regression analysis was performed to examine the associations between GAD1 SNPs and SZ.

Results

Ten SNPs covering GAD1 gene were analyzed in the discovery sample, and two SNPs showed nominal associations with SZ (rs2241165, P = 0.0181, OR = 1.261; rs2241164, P = 0.0225, OR = 1.219). SNP rs2241164 was also nominally significant in the independent replication sample (P = 0.0462, OR = 1.110), and the significance became stronger in a subsequent meta-analysis combining both discovery and replication samples (P = 0.00398, OR = 1.138). Nevertheless, such association could not survive multiple corrections, although the effect size of rs2241164 was comparable with other SZ risk loci identified in genome-wide association studies (GWAS) in Han Chinese population. We also examined the associations between GAD1 SNPs and SZ in published datasets of SZ GWAS in East Asians and Europeans, and no significant associations were observed.

Conclusion

We observed weak associations between GAD1 SNPs and risk of SZ in Han Chinese populations. Further analyses in larger Han Chinese samples with more detailed phenotyping are necessary to elucidate the genetic correlation between GAD1 SNPs and SZ.

GABAergic System Dysfunction and Challenges in Schizophrenia Research

Despite strenuous studies since the last century, the precise cause and pathology of schizophrenia are still largely unclear and arguably controversial. Although many hypotheses have been proposed to explain the etiology of schizophrenia, the definitive genes or core pathological mechanism remains absent. Among these hypotheses, however, GABAergic dysfunction stands out as a common feature consistently reported in schizophrenia, albeit a satisfactory mechanism that could be exploited for therapeutic purpose has not been developed yet. This review is focusing on the progress made to date in the field in terms of understanding the mechanisms involving dysfunctional GABAergic system and loops identified in schizophrenia research.

Loss of Calretinin in L5a impairs the formation of the barrel cortex leading to abnormal whisker-mediated behaviors

The rodent whisker-barrel cortex system has been established as an ideal model for studying sensory information integration. The barrel cortex consists of barrel and septa columns that receive information input from the lemniscal and paralemniscal pathways, respectively. Layer 5a is involved in both barrel and septa circuits and play a key role in information integration. However, the role of layer 5a in the development of the barrel cortex remains unclear. Previously, we found that calretinin is dynamically expressed in layer 5a. In this study, we analyzed calretinin KO mice and found that the dendritic complexity and length of layer 5a pyramidal neurons were significantly decreased after calretinin ablation. The membrane excitability and excitatory synaptic transmission of layer 5a neurons were increased. Consequently, the organization of the barrels was impaired. Moreover, layer 4 spiny stellate cells were not able to properly gather, leading to abnormal formation of barrel walls as the ratio of barrel/septum size obviously decreased. Calretinin KO mice exhibited deficits in exploratory and whisker-associated tactile behaviors as well as social novelty preference. Our study expands our knowledge of layer 5a pyramidal neurons in the formation of barrel walls and deepens the understanding of the development of the whisker-barrel cortex system.

Behavioral Consequences of a Combination of Gad1 Haplodeficiency and Adolescent Exposure to an NMDA Receptor Antagonist in Long-Evans Rats

Glutamate decarboxylase 67-kDa isoform (GAD67), which is encoded by the GAD1 gene, is one of the key enzymes that produce GABA. The reduced expression of GAD67 has been linked to the pathophysiology of schizophrenia. Additionally, the excitatory glutamatergic system plays an important role in the development of this disorder. Animal model studies have revealed that chronic blockade of NMDA-type glutamate receptors can cause GABAergic dysfunction and long-lasting behavioral abnormalities. Based on these findings, we speculated that Gad1 haplodeficiency combined with chronic NMDA receptor blockade would lead to larger behavioral consequences relevant to schizophrenia in a rat model. In this study, we administered an NMDAR antagonist, MK-801 (0.2 mg/kg), to CRISPR/Cas9-generated Gad1^+/− rats during adolescence to test this hypothesis. The MK-801 treated Gad1^+/− rats showed a shorter duration in each rearing episode in the open field test than the saline-treated Gad1^+/+ rats. In contrast, immobility in the forced swim test was increased and fear extinction was impaired in Gad1^+/− rats irrespective of MK-801 treatment. Interestingly, the time spent in the center region of the elevated plus-maze was significantly affected only in the saline-treated Gad1^+/− rats. Additionally, the MK-801-induced impairment of the social novelty preference was not observed in Gad1^+/− rats. These results suggest that the synergistic and additive effects of Gad1 haplodeficiency and NMDA receptor blockade during adolescence on the pathogenesis of schizophrenia may be more limited than expected. Findings from this study also imply that these two factors mainly affect negative or affective symptoms, rather than positive symptoms.

Interaction of maternal immune activation and genetic interneuronal inhibition

Genes and environment interact during intrauterine life, and potentially alter the developmental trajectory of the brain. This can result in life-long consequences on brain function. We have previously developed two transgenic mouse lines that suppress Gad1 expression in parvalbumin (PVALB) and neuropeptide Y (NPY) expressing interneuron populations using a bacterial artificial chromosome (BAC)-driven miRNA-based silencing technology. We were interested to assess if maternal immune activation (MIA), genetic interneuronal inhibition, and the combination of these two factors disrupt and result in long-term changes in neuroinflammatory gene expression, sterol biosynthesis, and acylcarnitine levels in the brain of maternally exposed offspring. Pregnant female WT mice were given a single intraperitoneal injection of saline or polyinosinic-polycytidilic acid [poly(I:C)] at E12.5. Brains of offspring were analyzed at postnatal day 90. We identified complex and persistent neuroinflammatory gene expression changes in the hippocampi of MIA-exposed offspring, as well in the hippocampi of Npy/Gad1 and Pvalb/Gad1 mice. In addition, both MIA and genetic inhibition altered the post-lanosterol sterol biosynthesis in the neocortex and disrupted the typical acylcarnitine profile. In conclusion, our findings suggest that both MIA and inhibition of interneuronal function have long-term consequences on critical homeostatic mechanisms of the brain, including immune function, sterol levels, and energy metabolism.

Global knockdown of glutamate decarboxylase 67 elicits emotional abnormality in mice

Reduced expression of glutamate decarboxylase 67 (GAD67), encoded by the Gad1 gene, is a consistent finding in postmortem brains of patients with several psychiatric disorders, including schizophrenia, bipolar disorder and major depressive disorder. The dysfunction of GAD67 in the brain is implicated in the pathophysiology of these psychiatric disorders; however, the neurobiological consequences of GAD67 dysfunction in mature brains are not fully understood because the homozygous Gad1 knockout is lethal in newborn mice. We hypothesized that the tetracycline-controlled gene expression/suppression system could be applied to develop global GAD67 knockdown mice that would survive into adulthood. In addition, GAD67 knockdown mice would provide new insights into the neurobiological impact of GAD67 dysfunction. Here, we developed Gad1^{tTA/STOP−tetO} biallelic knock-in mice using Gad1^STOP−tetO and Gad1^tTA knock-in mice, and compared them with Gad1^+/+ mice. The expression level of GAD67 protein in brains of Gad1^{tTA/STOP−tetO} mice treated with doxycycline (Dox) was decreased by approximately 90%. The GABA content was also decreased in the brains of Dox-treated Gad1^{tTA/STOP−tetO} mice. In the open-field test, Dox-treated Gad1^{tTA/STOP−tetO} mice exhibited hyper-locomotor activity and decreased duration spent in the center region. In addition, acoustic startle responses were impaired in Dox-treated Gad1^{tTA/STOP−tetO} mice. These results suggest that global reduction in GAD67 elicits emotional abnormalities in mice. These GAD67 knockdown mice will be useful for elucidating the neurobiological mechanisms of emotional abnormalities, such as anxiety symptoms associated with psychiatric disorders.

The Role of Parvalbumin Interneurons in Neurotransmitter Balance and Neurological Disease

While great progress has been made in the understanding of neurological illnesses, the pathologies, and etiologies that give rise to these diseases still remain an enigma, thus, also making treatments for them more challenging. For effective and individualized treatment, it is beneficial to identify the underlying mechanisms that govern the associated cognitive and behavioral processes that go awry in neurological disorders. Parvalbumin fast-spiking interneurons (Pv-FSI) are GABAergic cells that are only a small fraction of the brain's neuronal network, but manifest unique cellular and molecular properties that drastically influence the downstream effects on signaling and ultimately change cognitive behaviors. Proper brain functioning relies heavily on neuronal communication which Pv-FSI regulates, excitatory-inhibitory balances and GABAergic disinhibition between circuitries. This review highlights the depth of Pv-FSI involvement in the cortex, hippocampus, and striatum, as it pertains to expression, neurotransmission, role in neurological disorders, and dysfunction, as well as cognitive behavior and reward-seeking. Recent research has indicated that Pv-FSI play pivotal roles in the molecular pathophysiology and cognitive-behavioral deficits that are core features of many psychiatric disorders, such as schizophrenia, autism spectrum disorders, Alzheimer's disease, and drug addiction. This suggests that Pv-FSI could be viable targets for treatment of these disorders and thus calls for further examination of the undeniable impact Pv-FSI have on the brain and cognitive behavior.

Genetic deletion of the 67-kDa isoform of glutamate decarboxylase alters conditioned fear behavior in rats

The GABAergic system is thought to play an important role in the control of cognition and emotion, such as fear, and is related to the pathophysiology of psychiatric disorders. For example, the expression of the 67‐kDa isoform of glutamate decarboxylase (GAD67), a GABA‐producing enzyme, is downregulated in the postmortem brains of patients with major depressive disorder and schizophrenia. However, knocking out the Gad1 gene, which encodes GAD67, is lethal in mice, and thus, the association between Gad1 and cognitive/emotional functions is unclear. We recently developed Gad1 knockout rats and found that some of them can grow into adulthood. Here, we performed fear‐conditioning tests in adult Gad1 knockout rats to assess the impact of the loss of Gad1 on fear‐related behaviors and the formation of fear memory. In a protocol assessing both cued and contextual memory, Gad1 knockout rats showed a partial antiphase pattern of freezing during training and significantly excessive freezing during the contextual test compared with wild‐type rats. However, Gad1 knockout rats did not show any synchronous increase in freezing with auditory tones in the cued test. On the other hand, in a contextual memory specialized protocol, Gad1 knockout rats exhibited comparable freezing behavior to wild‐type rats, while their fear extinction was markedly impaired. These results suggest that GABA synthesis by GAD67 has differential roles in cued and contextual fear memory.

A Dendrite-Focused Framework for Understanding the Actions of Ketamine and Psychedelics

Pilot studies have hinted that serotonergic psychedelics such as psilocybin may relieve depression, and could possibly do so by promoting neural plasticity. Intriguingly, another psychotomimetic compound, ketamine, is a fast-acting antidepressant and induces synapse formation. The similarities in behavioral and neural effects have been puzzling because the compounds target distinct molecular receptors in the brain. In this opinion article, we develop a conceptual framework that suggests the actions of ketamine and serotonergic psychedelics may converge at the dendrites, to both enhance and suppress membrane excitability. We speculate that mismatches in the opposing actions on dendritic excitability may relate to these compounds' cell-type and region selectivity, their moderate range of effects and toxicity, and their plasticity-promoting capacities.

CRISPR/Cas9-engineered Gad1 elimination in rats leads to complex behavioral changes: implications for schizophrenia

GABAergic dysfunctions have been implicated in the pathogenesis of schizophrenia, especially the associated cognitive impairments. The GABA synthetic enzyme glutamate decarboxylase 67-kDa isoform (GAD67) encoded by the GAD1 gene is downregulated in the brains of patients with schizophrenia. Furthermore, a patient with schizophrenia harboring a homozygous mutation of GAD1 has recently been discovered. However, it remains unclear whether loss of function of GAD1 leads to the symptoms observed in schizophrenia, including cognitive impairment. One of the obstacles faced in experimental studies to address this issue is the perinatal lethality of Gad1 knockout (KO) mice, which precluded characterization at the adult stage. In the present study, we successfully generated Gad1 KO rats using CRISPR/Cas9 genome editing technology. Surprisingly, 33% of Gad1 KO rats survived to adulthood and could be subjected to further characterization. The GABA concentration in the Gad1 KO cerebrum was reduced to ~52% of the level in wild-type rats. Gad1 KO rats exhibited impairments in both spatial reference and working memory without affecting adult neurogenesis in the hippocampus. In addition, Gad1 KO rats showed a wide range of behavioral alterations, such as enhanced sensitivity to an NMDA receptor antagonist, hypoactivity in a novel environment, and decreased preference for social novelty. Taken together, the results suggest that Gad1 KO rats could provide a novel model covering not only cognitive deficits but also other aspects of the disorder. Furthermore, the present study teaches an important lesson: differences between species should be considered when developing animal models of human diseases.

Diffusible Tumor Necrosis Factor-Alpha (TNF-α) Promotes Noise-Induced Parvalbumin-Positive (PV+) Neuron Loss and Auditory Processing Impairments

Neuroinflammation has been implicated in noise-induced auditory processing disorder and tinnitus. Certain non-auditory neurological disorders can also increase the levels of proinflammatory cytokines in the brain. To investigate the impact of increased brain proinflammatory cytokine levels on the central auditory pathway, we infused recombinant TNF-α into the right lateral cerebral ventricle, and examined auditory processing and cytoarchitecture of the auditory cortex. Microglial deramification was observed in the auditory cortex of mice that had received both TNF-α infusion and exposure to an 86-dB noise, but not in mice that had received either TNF-α infusion or noise exposure alone. In addition, we observed reduced cortical PV+ neuron density and impaired performances in gap detection and prepulse inhibition (PPI) only in mice that received both TNF-α infusion and the noise exposure. These results suggest that disease-related increase in brain proinflammatory cytokine release could be a risk factor for noise-induced auditory processing disorder and tinnitus.

Modulating microglia activation prevents maternal immune activation induced schizophrenia-relevant behavior phenotypes via arginase 1 in the dentate gyrus

Prenatal infection during pregnancy increases the risk for developing neuropsychiatric disorders such as schizophrenia. This is linked to an inflammatory microglial phenotype in the offspring induced by maternal immune activation (MIA). Microglia are crucial for brain development and maintenance of neuronal niches, however, whether and how their activation is involved in the regulation of neurodevelopment remains unclear. Here, we used a MIA rodent model in which polyinosinic: polycytidylic acid (poly (I:C)) was injected into pregnant mice. We found fewer parvalbumin positive (PV+) cells and impaired GABAergic transmission in the dentate gyrus (DG), accompanied by schizophrenia-like behavior in the adult offspring. Minocycline, a potent inhibitor of microglia activation, successfully prevented the above-mentioned deficits in the offspring. Furthermore, by using microglia-specific arginase 1 (Arg1) ablation as well as overexpression in DG, we identified a critical role of Arg1 in microglia activation to protect against poly (I:C) imparted neuropathology and altered behavior in offspring. Taken together, our results highlight that Arg1-mediated alternative activation of microglia are potential therapeutic targets for psychiatric disorders induced by MIA.

GABAergic System in Stress: Implications of GABAergic Neuron Subpopulations and the Gut-Vagus-Brain Pathway

Stress can cause a variety of central nervous system disorders, which are critically mediated by the γ-aminobutyric acid (GABA) system in various brain structures. GABAergic neurons have different subsets, some of which coexpress certain neuropeptides that can be found in the digestive system. Accumulating evidence demonstrates that the gut-brain axis, which is primarily regulated by the vagus nerve, is involved in stress, suggesting a communication between the "gut-vagus-brain" pathway and the GABAergic neuronal system. Here, we first summarize the evidence that the GABAergic system plays an essential role in stress responses. In addition, we review the effects of stress on different brain regions and GABAergic neuron subpopulations, including somatostatin, parvalbumin, ionotropic serotonin receptor 5-HT3a, cholecystokinin, neuropeptide Y, and vasoactive intestinal peptide, with regard to signaling events, behavioral changes, and pathobiology of neuropsychiatric diseases. Finally, we discuss the gut-brain bidirectional communications and the connection of the GABAergic system and the gut-vagus-brain pathway.

Downregulation of parvalbumin expression in the prefrontal cortex during adolescence causes enduring prefrontal disinhibition in adulthood

The expression of the calcium binding protein parvalbumin (PV) has been observed in several cortical regions during development in a temporal pattern consistent with increased afferent-dependent activity. In the prefrontal cortex (PFC), PV expression appears last and continues to substantially increase throughout adolescence, yet the significance of this increase remains unclear. Because of the expression of PV in fast-spiking GABAergic interneurons, we hypothesized that PV upregulation during adolescence is necessary to sustain the increase in GABAergic activity observed in the PFC during this period. To test this hypothesis, we utilized an RNAi strategy to directly downregulate PV levels in the PFC during adolescence and examined its impact on prefrontal GABAergic function, plasticity, and associated behaviors during adulthood. The data indicate that a mere 25% reduction of adult PV levels in the PFC was sufficient to reduce local GABAergic transmission onto pyramidal neurons, disrupt prefrontal excitatory-inhibitory balance, and alter processing of afferent information from the ventral hippocampus. Accordingly, these animals displayed an impairment in the level of extinction learning of a trace fear conditioning response, a behavioral paradigm that requires intact PFC-ventral hippocampus connectivity. These results indicate the PV upregulation observed in the PFC during adolescence is necessary for refinement of prefrontal GABAergic function, the absence of which results in immature afferent processing and a hypofunctional state. Importantly, these results suggest there is a critical window of plasticity during which PV upregulation supports the acquisition of mature GABAergic phenotype necessary to sustain adult PFC functions.

Calcium-binding proteins are altered in the cerebellum in schizophrenia

Alterations in the cortico-cerebellar-thalamic-cortical circuit might underlie the diversity of symptoms in schizophrenia. However, molecular changes in cerebellar neuronal circuits, part of this network, have not yet been fully determined. Using LC-MS/MS, we screened altered candidates in pooled grey matter of cerebellum from schizophrenia subjects who committed suicide (n = 4) and healthy individuals (n = 4). Further validation by immunoblotting of three selected candidates was performed in two cohorts comprising schizophrenia (n = 20), non-schizophrenia suicide (n = 6) and healthy controls (n = 21). We found 99 significantly altered proteins, 31 of them previously reported in other brain areas by proteomic studies. Transport function was the most enriched category, while cell communication was the most prevalent function. For validation, we selected the vacuolar proton pump subunit 1 (VPP1), from transport, and two EF-hand calcium-binding proteins, calmodulin and parvalbumin, from cell communication. All candidates showed significant changes in schizophrenia (n = 7) compared to controls (n = 7). VPP1 was altered in the non-schizophrenia suicide group and increased levels of parvalbumin were linked to antipsychotics. Further validation in an independent cohort of non-suicidal chronic schizophrenia subjects (n = 13) and non-psychiatric controls (n = 14) showed that parvalbumin was increased, while calmodulin was decreased in schizophrenia. Our findings provide evidence of calcium-binding protein dysregulation in the cerebellum in schizophrenia, suggesting an impact on normal calcium-dependent synaptic functioning of cerebellar circuits. Our study also links VPP1 to suicide behaviours, suggesting a possible impairment in vesicle neurotransmitter refilling and release in these phenotypes.

Polymorphisms in CRYBB2 encoding βB2-crystallin are associated with antisaccade performance and memory function

βB2-crystallin (gene symbol: Crybb2/CRYBB2) was first described as a structural protein of the ocular lens before it was detected in various brain regions of the mouse, including the hippocampus and the cerebral cortex. Mutations in the mouse Crybb2 gene lead to alterations of sensorimotor gating measured as prepulse inhibition (PPI) and reduced hippocampal size, combined with an altered number of parvalbumin-positive GABAergic interneurons. Decreased PPI and alterations of parvalbumin-positive interneurons are also endophenotypes that typically occur in schizophrenia. To verify the results found in mice, we genotyped 27 single nucleotide polymorphisms (SNPs) within the CRYBB2 gene and its flanking regions and investigated different schizophrenia typical endophenotypes in a sample of 510 schizophrenia patients and 1322 healthy controls. In the case-control study, no association with schizophrenia was found. However, 3 of the 4 investigated haplotype blocks indicated a decreased CRYBB2 mRNA expression. Two of these blocks were associated with poorer antisaccade task performance and altered working memory-linked functional magnetic resonance imaging signals. For the two haplotypes associated with antisaccade performance, suggestive evidence was found with visual memory and in addition, haplotype block 4 showed a nominally significant association with reduced sensorimotor gating, measured as P50 ratio. These results were not schizophrenia-specific, but could be detected in a combined sample of patients and healthy controls. This is the first study to demonstrate the importance of βB2-crystallin for antisaccade performance and memory function in humans and therefore provides implications for βB2-crystallin function in the human brain.

Overinhibition mediated by parvalbumin interneurons might contribute to depression-like behavior and working memory impairment induced by lipopolysaccharide challenge

Systemic inflammation induces cognitive impairments via unclear mechanisms. Accumulating evidence has demonstrated that a subset of neurons that express parvalbumin (PV) play a critical role in regulation of cognitive and emotional behavior. Thus, the aim of the present study was to test whether disruption of PV interneuron mediates systemic inflammation-induced depression-like behavior and working memory impairment by lipopolysaccharide (LPS) challenge. Here we showed that LPS induces depression-like behavior and working memory impairment, coinciding with increased PV expression, enhanced GABAergic transmission, and impaired long-term potentiation (LTP) in the hippocampus. Notably, systemic administration of NMDA (N-methyl-D-aspartate) receptor (NMDAR) antagonist ketamine was able to interfere with PV expression and reverse depression-like behavior and working memory impairment, which is probably mediated by reversing impaired LTP. In addition, flumazenil, a competitive antagonist acting at the benzodiazepine binding site of the GABA_A receptor, also ameliorated these abnormal behaviors. Collectively, our study added growing evidence to the limited studies that overinhibition mediated by PV interneurons might play a critical role in LPS-induced depression-like behavior and working memory impairment.

Transcriptome analysis of fibroblasts from schizophrenia patients reveals differential expression of schizophrenia-related genes

Schizophrenia is a complex neurodevelopmental disorder with high rate of morbidity and mortality. While the heritability rate is high, the precise etiology is still unknown. Although schizophrenia is a central nervous system disorder, studies using peripheral tissues have also been established to search for patient specific biomarkers and to increase understanding of schizophrenia etiology. Among all peripheral tissues, fibroblasts stand out as they are easy to obtain and culture. Furthermore, they keep genetic stability for long period and exhibit molecular similarities to cells from nervous system. Using a unique set of fibroblast samples from a genetically isolated population in northern Sweden, we performed whole transcriptome sequencing to compare differentially expressed genes in seven controls and nine patients. We found differential fibroblast expression between cases and controls for 48 genes, including eight genes previously implicated in schizophrenia or schizophrenia related pathways; HGF, PRRT2, EGR1, EGR3, C11orf87, TLR3, PLEKHH2 and PIK3CD. Weighted gene correlation network analysis identified three differentially co-expressed networks of genes significantly-associated with schizophrenia. All three modules were significantly suppressed in patients compared to control, with one module highly enriched in genes involved in synaptic plasticity, behavior and synaptic transmission. In conclusion, our results support the use of fibroblasts for identification of differentially expressed genes in schizophrenia and highlight dysregulation of synaptic networks as an important mechanism in schizophrenia.

Region-specific Effects of Maternal Separation on Perineuronal Net and Parvalbumin-expressing Interneuron Formation in Male and Female Rats

Early life experiences play a vital role in contributing to healthy brain development. Adverse experiences have a lasting impact on the prefrontal cortex (PFC) and basolateral amygdala (BLA), brain regions associated with emotion regulation. Early life adversity via maternal separation (MS) has sex-specific effects on expression of parvalbumin (PV), which is expressed in fast-spiking GABAergic interneurons that are preferentially enwrapped by perineuronal nets (PNNs). Importantly, PNN formation coincides with the closure of developmental critical periods and regulates PV-expressing interneuron activity. Since aberrant PNN organization has been reported following adverse experiences in adolescent and adult rats, we investigated the impact of adversity early in life in the form of MS on the developing brain. Rat pups were separated from their dams for 4 h per day from postnatal day (P) 2-20. Tissue sections from juvenile (P20), adolescent (P40), and early adult (P70) animals containing the PFC and BLA were fluorescently stained to visualize Wisteria floribunda agglutinin+ PNNs and PV-expressing interneurons, and density and intensity was quantified. Our results confirm past reports that PFC PNNs form gradually throughout development; however, PNN density plateaus in adolescence, while intensity continues to increase into adulthood. Importantly, MS delays PNN formation in the prelimbic PFC and results in sex-specific aberrations in PNN structural integrity that do not appear until adulthood. The present findings reveal sex-, age-, and region-specific effects of early life adversity on PNN and PV maturation, implicating neuroplastic alterations following early life adversity that may be associated with sex differences in psychopathology and resilience.

The regulation of glutamic acid decarboxylases in GABA neurotransmission in the brain

Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter that is required for the control of synaptic excitation/inhibition and neural oscillation. GABA is synthesized by glutamic acid decarboxylases (GADs) that are widely distributed and localized to axon terminals of inhibitory neurons as well as to the soma and, to a lesser extent, dendrites. The expression and activity of GADs is highly correlated with GABA levels and subsequent GABAergic neurotransmission at the inhibitory synapse. Dysregulation of GADs has been implicated in various neurological disorders including epilepsy and schizophrenia. Two isoforms of GADs, GAD67 and GAD65, are expressed from separate genes and have different regulatory processes and molecular properties. This review focuses on the recent advances in understanding the structure of GAD, its transcriptional regulation and post-transcriptional modifications in the central nervous system. This may provide insights into the pathological mechanisms underlying neurological diseases that are associated with GAD dysfunction.

Molecular expression profiles of morphologically defined hippocampal neuron types: Empirical evidence and relational inferences

Gene and protein expressions are key determinants of cellular function. Neurons are the building blocks of brain circuits, yet the relationship between their molecular identity and the spatial distribution of their dendritic inputs and axonal outputs remains incompletely understood. The open-source knowledge base Hippocampome.org amasses such transcriptomic data from the scientific literature for morphologically defined neuron types in the rodent hippocampal formation: dentate gyrus, CA3, CA2, CA1, subiculum, and entorhinal cortex. Positive, negative, or mixed expression reports were initially obtained from published articles directly connecting molecular evidence to neurons with known axonal and dendritic patterns across hippocampal layers. Here, we supplement this information by collating, formalizing, and leveraging relational expression inferences that link a gene or protein expression or lack thereof to that of another molecule or to an anatomical location. With these additional interpretations, we freely release online a comprehensive human- and machine-readable molecular profile for more than 100 neuron types in Hippocampome.org. Analysis of these data ascertains the ability to distinguish unequivocally most neuron types in each of the major subdivisions of the hippocampus based on currently known biochemical markers. Moreover, grouping neuron types by expression similarity reveals eight superfamilies characterized by a few defining molecules.

The Fragile Brain: Stress Vulnerability, Negative Affect and GABAergic Neurocircuits in Psychosis

Persons with schizophrenia exhibit sensitivity to stress and negative affect (NA), both strongly correlated with poor functional outcome. This theoretical review suggests that NA reflects a "fragile brain," ie, vulnerable to stress, including events not experienced as stressful by healthy individuals. Based on postmortem evidence of altered gamma-aminobutyric acid (GABA) function in parvalbumin positive interneurons (PVI), animal models of PVI abnormalities and neuroimaging data with GABAergic challenge, it is suggested that GABAergic disruptions weaken cortical regions, which leads to stress vulnerability and excessive NA. Neurocircuits that respond to stressful and salient environmental stimuli, such as the hypothalamic-pituitary-adrenal axis and the amygdala, are highly dysregulated in schizophrenia, exhibiting hypo- and hyper-activity. PVI abnormalities in lateral prefrontal cortex and hippocampus have been hypothesized to affect cognitive function and positive symptoms, respectively; in the medial frontal cortex (dorsal anterior cingulate cortex and dorsal medial prefrontal cortex), these abnormalities may lead to vulnerability to stress, NA and dysregulation of stress responsive systems. Given that postmortem PVI disruptions have been identified in other conditions, such as bipolar disorder and autism, stress vulnerability may reflect a transdiagnostic dimension of psychopathology.

Enriched Environment Reverts Somatostatin Interneuron Loss in MK-801 Model of Schizophrenia

Dysregulation of the inhibitory drive has been proposed to be a central mechanism to explain symptoms and pathophysiological hallmarks in schizophrenia. A number of recent neuroanatomical studies suggest that certain types of inhibitory cells are deficient in schizophrenia, including somatostatin-immunoreactive interneurons (SST+). The present study sought to use stereological methods to investigate whether the number of SST+ interneurons decreased after repeated injections of NMDA receptor antagonist MK-801 (0.5 mg/kg) and to determine the effect of limited exposure to an enriched environment (EE) in adult life on this sub-population of inhibitory cells. Considering that somatostatin expression is highly dependent on neurotrophic support, we explored the changes in the relative expression of proteins related to brain-derived neurotrophic factor-tyrosine kinase B (BDNF-TrkB) signaling between the experimental groups. We observed that early-life MK-801 treatment significantly decreased the number of SST+ interneurons in the medial prefrontal cortex (mPFC) and the hippocampus (HPC) of adult Long Evans rats. Contrarily, short-term exposure to EE increased the number of SST+ interneurons in MK-801-injected animals, except in the CA1 region of the hippocampus, whereas this increase was not observed in vehicle-injected rats. We also found upregulated BDNF-TrkB signaling after EE that triggered an increase in the pERK/ERK ratio in mPFC and HPC, and the pAkt/Akt ratio in HPC. Thus, the present results support the notion that SST+ interneurons are markedly affected after early-life NMDAR blockade and that EE promotes SST+ interneuron expression, which is partly mediated through the BDNF-TrkB signaling pathway. These results may have important implications for schizophrenia, as SST+ interneuron loss is also observed in the MK-801 pre-clinical model, and its expression can be rescued by non-pharmacological approaches.

Crybb2 Mutations Consistently Affect Schizophrenia Endophenotypes in Mice

As part of the βγ-superfamily, βB2-crystallin (CRYBB2) is an ocular structural protein in the lens, and mutation of the corresponding gene can cause cataracts. CRYBB2 also is expressed in non-lens tissue such as the adult mouse brain and is associated with neuropsychiatric disorders such as schizophrenia. Nevertheless, the robustness of this association as well as how CRYBB2 may contribute to disease-relevant phenotypes is unknown. To add further clarity to this issue, we performed a comprehensive analysis of behavioral and neurohistological alterations in mice with an allelic series of mutations in the C-terminal end of the Crybb2 gene. Behavioral phenotyping of these three βB2-mutant lines Crybb2O377, Crybb2Philly, and Crybb2Aey2 included assessment of exploratory activity and anxiety-related behavior in the open field, sensorimotor gating measured by prepulse inhibition (PPI) of the acoustic startle reflex, cognitive performance measured by social discrimination, and spontaneous alternation in the Y-maze. In each mutant line, we also quantified the number of parvalbumin-positive (PV+) GABAergic interneurons in selected brain regions that express CRYBB2. While there were allele-specific differences in individual behaviors and affected brain areas, all three mutant lines exhibited consistent alterations in PPI that paralleled alterations in the PV+ cell number in the thalamic reticular nucleus (TRN). The direction of the PPI change mirrored that of the TRN PV+ cell number thereby suggesting a role for TRN PV+ cell number in modulating PPI. Moreover, as both altered PPI and PV+ cell number are schizophrenia-associated endophenotypes, our result implicates mutated Crybb2 in the development of this neuropsychiatric disorder.