PV Interneurons: Critical Regulators of E/I Balance for Prefrontal Cortex-Dependent Behavior and Psychiatric Disorders

Complex housing in adulthood state-dependently affects the excitation-inhibition balance in the infralimbic prefrontal cortex of male C57Bl/6 mice

The prefrontal cortex (PFC) plays an important role in social behavior and is sensitive to stressful circumstances. Challenging life conditions might change PFC function and put individuals at risk for maladaptive social behavior. The excitation-inhibition (EI) balance of prefrontal neurons appears to play a crucial role in this process. Here, we examined how a challenging life condition in C57BL/6JolaHsd mice, i.e. group-housing 6 mice in a complex environment for 10 days in adulthood, changes the EI-balance of infralimbic prefrontal neurons in layer 2/3, compared to standard pair-housing. Slices were prepared from "undisturbed" mice, i.e. the first mouse taken from the cage, or mice taken ∼15 min later, who were mildly aroused after removal of the first mouse. We observed a housing-condition by arousal-state interaction, with in the complex housing group an elevated EI-balance in undisturbed and reduced EI-balance in mildly aroused animals, while no differences were observed in standard housed animals. The change was explained by a shift in mIPSC and mEPSC frequency, while amplitudes remained unaffected. Female mice showed no housing-by-state interaction, but a main effect of housing was found for mIPSCs, with a higher frequency in complex- versus standard-housed females. No effects were observed in males who were complex-housed from a young age onwards. Explorative investigations support a potential mediating role of corticosterone in housing effects on the EI-balance of males. We argue that taking the arousal state of individuals into account is necessary to better understand the consequences of exposure to challenging life conditions for prefrontal function.

Aberrant glutamatergic systems underlying impulsive behaviors: Insights from clinical and preclinical research

Impulsivity is a broad construct that often refers to one of several distinct behaviors and can be measured with self-report questionnaires and behavioral paradigms. Several psychiatric conditions are characterized by one or more forms of impulsive behavior, most notably the impulsive/hyperactive subtype of attention-deficit/hyperactivity disorder (ADHD), mood disorders, and substance use disorders. Monoaminergic neurotransmitters are known to mediate impulsive behaviors and are implicated in various psychiatric conditions. However, growing evidence suggests that glutamate, the major excitatory neurotransmitter of the mammalian brain, regulates important functions that become dysregulated in conditions like ADHD. The purpose of the current review is to discuss clinical and preclinical evidence linking glutamate to separate aspects of impulsivity, specifically motor impulsivity, impulsive choice, and affective impulsivity. Hyperactive glutamatergic activity in the corticostriatal and the cerebro-cerebellar pathways are major determinants of motor impulsivity. Conversely, hypoactive glutamatergic activity in frontal cortical areas and hippocampus and hyperactive glutamatergic activity in anterior cingulate cortex and nucleus accumbens mediate impulsive choice. Affective impulsivity is controlled by similar glutamatergic dysfunction observed for motor impulsivity, except a hyperactive limbic system is also involved. Loss of glutamate homeostasis in prefrontal and nucleus accumbens may contribute to motor impulsivity/affective impulsivity and impulsive choice, respectively. These results are important as they can lead to novel treatments for those with a condition characterized by increased impulsivity that are resistant to conventional treatments.

Inhibition of prefrontal cortex parvalbumin interneurons mitigates behavioral and physiological sequelae of chronic stress in male mice

Chronic stress leads to hypofunction of the medial prefrontal cortex (mPFC), mechanisms of which remain to be determined. Enhanced activation of GABAergic of parvalbumin (PV) expressing interneurons (INs) is thought to play a role in stress-induced prefrontal inhibition. In this study, we tested whether chemogenetic inhibition of mPFC PV INs after chronic stress can rescue chronic stress-related behavioral and physiological phenotypes. Mice underwent 2 weeks of chronic variable stress (CVS) followed by a battery of behavioral tests known to be affected by chronic stress exposure, e.g. an open field (OF), novel object recognition (NOR), tail suspension test (TST), sucrose preference test (SPT), and light dark (LD) box. Inhibitory DREADDs were actuated by 3 mg/kg CNO administered 30 min prior to each behavioral test. CVS caused hyperactivity in the OF, reduced sucrose preference in the SPT (indicative of enhanced anhedonia), and increased anxiety-like behavior in the LD box. Inhibition of PV IN after stress mitigated these effects. In addition, CVS also resulted in reduced thymus weight and body weight loss, which were also mitigated by PV IN inhibition. Our results indicate that chronic stress leads to plastic changes in PV INs that may be mitigated by chemogenetic inhibition. Our findings implicate cortical GABAergic INs as a therapeutic target in stress-related diseases.

Parvalbumin interneuron mGlu5 receptors govern sex differences in prefrontal cortex physiology and binge drinking

Despite established sex differences in the prevalence and presentation of psychiatric disorders, little is known about the cellular and synaptic mechanisms that guide these differences under basal conditions. The proper function of the prefrontal cortex (PFC) is essential for the top-down regulation of motivated behaviors. The activity of the PFC is tightly controlled by parvalbumin-expressing interneurons (PV-INs), a key subpopulation of fast-spiking GABAergic cells that regulate cortical excitability through direct innervations onto the perisomatic regions of nearby pyramidal cells. Recent rodent studies have identified notable sex differences in PV-IN activity and adaptations to experiences such as binge drinking. Here, we investigated the cellular and molecular mechanisms that underlie sex-specific regulation of PFC PV-IN function. Using whole-cell patch-clamp electrophysiology and selective pharmacology, we report that PV-INs from female mice are more excitable than those from males. Moreover, we find that mGlu1 and mGlu5 metabotropic glutamate receptors regulate cell excitability, excitatory drive, and endocannabinoid signaling at PFC PV-INs in a sex-dependent manner. Genetic deletion of mGlu5 receptors from PV-expressing cells abrogates all sex differences observed in PV-IN membrane and synaptic physiology. Lastly, we report that female, but not male, PV-mGlu5-/- mice exhibit decreased voluntary drinking on an intermittent access schedule, which could be related to changes in ethanol's stimulant properties. Importantly, these studies identify mGlu1 and mGlu5 receptors as candidate signaling molecules involved in sex differences in PV-IN activity and behaviors relevant to alcohol use.

Mu and Delta Opioid Receptors Modulate Inhibition within the Prefrontal Cortex Through Dissociable Cellular and Molecular Mechanisms

Aberrant signaling within cortical inhibitory microcircuits has been identified as a common signature of neuropsychiatric disorders. Interneuron (IN) activity is precisely regulated by neuromodulatory systems that evoke widespread changes in synaptic transmission and principal cell output. Cortical interneurons express high levels of Mu and Delta opioid receptors (MOR and DOR), positioning opioid signaling as a critical regulator of inhibitory transmission. However, we lack a complete understanding of how MOR and DOR regulate prefrontal cortex (PFC) microcircuitry. Here, we combine whole-cell patch-clamp electrophysiology, optogenetics, and viral tools to provide an extensive characterization MOR and DOR regulation of inhibitory transmission. We show that DOR activation is more effective at suppressing spontaneous inhibitory transmission in the prelimbic PFC, while MOR causes a greater acute suppression of electrically-evoked GABA release. Cell type-specific optogenetics revealed that MOR and DOR differentially regulate inhibitory transmission from parvalbumin, somatostatin, cholecystokinin, and vasoactive intestinal peptide-expressing INs. Finally, we demonstrate that DOR regulates inhibitory transmission through pre- and postsynaptic modifications to IN physiology, whereas MOR function is predominantly observed in somato-dendritic or presynaptic compartments depending on cell type.

Significance Statement

The endogenous opioid system regulates behaviors that rely on prefrontal cortex (PFC) function. Previous studies have described Mu and Delta opioid receptor expression within cortical GABAergic interneurons, but a detailed understanding of how opioids regulate different interneuron subtypes and cortical microcircuits has not been reported. We use whole-cell patch-clamp electrophysiology, genetically engineered mice, and optogenetics to assess MOR and DOR regulation of PFC inhibitory transmission, demonstrating that MOR and DOR inhibition of interneurons display qualitative and quantitative variation across GABAergic circuits within mouse prelimbic PFC.

Low-frequency repetitive transcranial magnetic stimulation for the treatment of post-traumatic stress disorder and its comparison with high-frequency stimulation: a systematic review and meta-analysis

Background

Repetitive transcranial magnetic stimulation (rTMS) showed potentially beneficial effects for the treatment of post-traumatic stress disorder (PTSD). Low-frequency (LF) rTMS decreases neuronal excitability and may have better safety compared to high-frequency (HF) rTMS. However, there lacks meta-analysis specifically focusing on LF rTMS.

Objectives

To specifically explore the efficacy and safety of LF rTMS for treating PTSD.

Methods

Databases including PubMed, EMBASE, MEDLINE, and Web of Science were systematically searched from inception to October 17, 2023. Both randomized controlled trials (RCTs) and open trials of LF rTMS on PTSD were included, and we additionally included RCTs comparing HF rTMS and sham treatment on PTSD. First, we qualitatively summarized parameters of LF rTMS treatment; then, we extracted data from the LF rTMS treatment subgroups of these studies to examine its effect size and potential influencing factors; third, we compared the effect sizes among LF rTMS, HF rTMS and sham treatment through network meta-analysis of RCTs.

Results

In all, 15 studies with a sample size of 542 participants were included. The overall effect size for LF rTMS as a treatment for PTSD was found as Hedges' g = 1.02 (95% CI (0.56, 1.47)). Meta-regression analysis did not reveal any influencing factors. Network meta-analysis showed that compared to sham treatment, only HF rTMS on the right dorsolateral prefrontal cortex (DLPFC) demonstrated a significant advantage in ameliorating PTSD symptoms, while LF rTMS on the right DLPFC showed a trend toward advantage, but the difference was not significant.

Conclusion

The current literature shows LF rTMS has effect in treating PTSD caused by various traumatic events. However, present limited number of RCT studies only showed LF rTMS to have a trend of advantage compared to sham treatment in treating PTSD caused by external traumatic events. In the future, more RCTs are needed to be made to confirm the efficacy of LF rTMS. Additionally, studies are required to elucidate the underlying mechanism in order to further improve its efficacy in different traumatic populations.

PROSPERO registration number

CRD42023470169.

Human α-synuclein aggregation activates ferroptosis leading to parvalbumin interneuron degeneration and motor learning impairment

The accumulation of α-synuclein induces neuronal loss in midbrain nuclei and leads to the disruption of motor circuits, while the pathology of α-synuclein in cortical regions remains elusive. To better characterize cortical synucleinopathy, here we generate a mouse model with the overexpression of human α-synuclein in the primary motor cortex (M1) of mice. A combination of molecular, in vivo recording, and behavioral approaches reveal that cortical expression of human α-synuclein results in the overexcitation of cortical pyramidal neurons (PNs), which are regulated by the decreased inhibitory inputs from parvalbumin-interneurons (PV-INs) to impair complex motor skill learning. Further mechanistic dissections reveal that human α-synuclein aggregation activates ferroptosis, contributing to PV-IN degeneration and motor circuit dysfunction. Taken together, the current study adds more knowledge to the emerging role and pathogenic mechanism of ferroptosis in neurodegenerative diseases.

The excitatory-inhibitory balance as a target for the development of novel drugs to treat schizophrenia

The intricate balance between excitation and inhibition (E/I) in the brain plays a crucial role in normative information processing. Dysfunctions in the E/I balance have been implicated in various psychiatric disorders, including schizophrenia (SCZ). In particular, abnormalities in GABAergic signaling, specifically in parvalbumin (PV)-containing interneurons, have been consistently observed in SCZ pathophysiology. PV interneuron function is vital for maintaining an ideal E/I balance, and alterations in PV interneuron-mediated inhibition contribute to circuit deficits observed in SCZ, including hippocampus hyperactivity and midbrain dopamine system overdrive. While current antipsychotic medications primarily target D2 dopamine receptors and are effective primarily in treating positive symptoms, novel therapeutic strategies aiming to restore the E/I balance could potentially mitigate not only positive symptoms but also negative symptoms and cognitive deficits. This could involve, for instance, increasing the inhibitory drive onto excitatory neurons or decreasing the putative enhanced pyramidal neuron activity due to functional loss of PV interneurons. Compounds targeting the glycine site at glutamate NMDA receptors and muscarinic acetylcholine receptors on PV interneurons that can increase PV interneuron drive, as well as drugs that increase the postsynaptic action of GABA, such as positive allosteric modulators of α5-GABA-A receptors, and decrease glutamatergic output, such as mGluR2/3 agonists, represent promising approaches. Preventive strategies aiming at E/I balance also represent a path to reduce the risk of transitioning to SCZ in high-risk individuals. Therefore, compounds with novel mechanisms targeting E/I balance provide optimism for more effective and tailored interventions in the management of SCZ.

Altered prefrontal and cerebellar parvalbumin neuron counts are associated with cognitive changes in male rats

Exposure to valproic acid (VPA), a common anti-seizure medication, in utero is a risk factor for autism spectrum disorder (ASD). People with ASD often display changes in the cerebellum, including volume changes, altered circuitry, and changes in Purkinje cell populations. ASD is also characterized by changes in the medial prefrontal cortex (mPFC), where excitatory/inhibitory balance is often altered. This study exposed rats to a high dose of VPA during gestation and assessed cognition and anxiety-like behaviors during young adulthood using a set-shifting task and the elevated plus maze. Inhibitory parvalbumin-expressing (PV +) neuron counts were assessed in the mPFC and cerebellar lobules VI and VII (Purkinje cell layers), which are known to modulate cognition. VPA males had increased PV + counts in crus I and II of lobule VII. VPA males also had decreased parvalbumin-expressing neuron counts in the mPFC. It was also found that VPA-exposed rats, regardless of sex, had increased parvalbumin-expressing Purkinje cell counts in lobule VI. In males, this was associated with impaired intra-dimensional shifting on a set-shifting task. Purkinje cell over proliferation may be contributing to the previously observed increase in volume of Lobule VI. These findings suggest that altered inhibitory signaling in cerebellar-frontal circuits may contribute to the cognitive deficits that occur within ASD.

Inhibitory mechanisms in the prefrontal-cortex differentially mediate Putamen activity during valence-based learning

Learning from appetitive and aversive stimuli involves interactions between the prefrontal cortex and subcortical structures. Preclinical and theoretical studies indicate that inhibition is essential in regulating the relevant neural circuitry. Here, we demonstrate that GABA, the main inhibitory neurotransmitter in the central nervous system, differentially affects how the dACC interacts with subcortical structures during appetitive and aversive learning in humans. Participants engaged in tasks involving appetitive and aversive learning, while using functional magnetic resonance spectroscopy (MRS) at 7T to track GABA concentrations in the dACC, alongside whole-brain fMRI scans to assess BOLD activation. During appetitive learning, dACC GABA concentrations were negatively correlated with learning performance and BOLD activity measured from the dACC and the Putamen. These correlations were absent during aversive learning, where dACC GABA concentrations negatively correlated with the connectivity between the dACC and the Putamen. Our results show that inhibition in the dACC mediates appetitive and aversive learning in humans through distinct mechanisms.

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.

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 pathway dysregulation in PV cells drives disease pathogenesis, we have developed a transgenic line that permits cell-type specific overexpression of the schizophrenia-associated C4 gene. We found that overexpression of mouse C4 (mC4) in PV cells causes sex-specific alterations in anxiety-like behavior and deficits in synaptic connectivity and excitability of PFC PV cells. Using a computational model, 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 perturbations of this neuroimmune gene in fast-spiking neurons are especially detrimental to circuits associated with anxiety-like behavior. Together, these results provide a causative link between C4 and the vulnerability of PV cells in brain disease.

miRNA-mediated control of gephyrin synthesis drives sustained inhibitory synaptic plasticity

Activity-dependent protein synthesis is crucial for long-lasting forms of synaptic plasticity. However, our understanding of translational mechanisms controlling GABAergic synapses is limited. One distinct form of inhibitory long-term potentiation (iLTP) enhances postsynaptic clusters of GABAARs and the primary inhibitory scaffold, gephyrin, to promote sustained synaptic strengthening. While we previously found that persistent iLTP requires mRNA translation, the mechanisms controlling plasticity-induced gephyrin translation remain unknown. We identify miR153 as a novel regulator of Gphn mRNA translation which controls gephyrin protein levels and synaptic clustering, ultimately impacting inhibitory synaptic structure and function. iLTP induction downregulates miR153, reversing its translational suppression of Gphn mRNA and promoting de novo gephyrin protein synthesis and synaptic clustering during iLTP. Finally, we find that reduced miR153 expression during iLTP is driven by an excitation-transcription coupling pathway involving calcineurin, NFAT and HDACs, which also controls the miRNA-dependent upregulation of GABAARs. Together, we delineate a miRNA-dependent post-transcriptional mechanism that controls the expression of the key synaptic scaffold, gephyrin, and may converge with parallel miRNA pathways to coordinate gene upregulation to maintain inhibitory synaptic plasticity.

Unique Transcriptomic Cell Types of the Granular Retrosplenial Cortex are Preserved Across Mice and Rats Despite Dramatic Changes in Key Marker Genes

The granular retrosplenial cortex (RSG) supports key functions ranging from memory consolidation to spatial navigation. The mouse RSG contains several cell types that are remarkably distinct from those found in other cortical regions. This includes the physiologically and transcriptomically unique low rheobase neuron that is the dominant cell-type in RSG layers 2/3 (L2/3 LR), as well as the similarly exclusive pyramidal cells that comprise much of RSG layer 5a (L5a RSG). While the functions of the RSG are extensively studied in both mice and rats, it remains unknown if the transcriptomically unique cell types of the mouse RSG are evolutionarily conserved in rats. Here, we show that mouse and rat RSG not only contain the same cell types, but key subtypes including the L2/3 LR and L5a RSG neurons are amplified in their representations in rats compared to mice. This preservation of cell types in male and female rats happens despite dramatic changes in key cell-type-specific marker genes, with the Scnn1a expression that selectively tags mouse L5a RSG neurons completely absent in rats. Important for Cre-driver line development, we identify alternative, cross-species genes that can be used to selectively target the cell types of the RSG in both mice and rats. Our results show that the unique cell types of the RSG are evolutionarily conserved across millions of years of evolution between mice and rats, but also emphasize stark species-specific differences in marker genes that need to be considered when making cell-type-specific transgenic lines of mice versus rats.

Monoaminergic Modulation of Learning and Cognitive Function in the Prefrontal Cortex

Extensive research has shed light on the cellular and functional underpinnings of higher cognition as influenced by the prefrontal cortex. Neurotransmitters act as key regulatory molecules within the PFC to assist with synchronizing cognitive state and arousal levels. The monoamine family of neurotransmitters, including dopamine, serotonin, and norepinephrine, play multifaceted roles in the cognitive processes behind learning and memory. The present review explores the organization and signaling patterns of monoamines within the PFC, as well as elucidates the numerous roles played by monoamines in learning and higher cognitive function.

Multi-level therapeutic actions of cannabidiol in ketamine-induced schizophrenia psychopathology in male rats

Repeated administration of ketamine (KET) has been used to model schizophrenia-like symptomatology in rodents, but the psychotomimetic neurobiological and neuroanatomical underpinnings remain elusive. In parallel, the unmet need for a better treatment of schizophrenia requires the development of novel therapeutic strategies. Cannabidiol (CBD), a major non-addictive phytocannabinoid has been linked to antipsychotic effects with unclear mechanistic basis. Therefore, this study aims to clarify the neurobiological substrate of repeated KET administration model and to evaluate CBD's antipsychotic potential and neurobiological basis. CBD-treated male rats with and without prior repeated KET administration underwent behavioral analyses, followed by multilevel analysis of different brain areas including dopaminergic and glutamatergic activity, synaptic signaling, as well as electrophysiological recordings for the assessment of corticohippocampal and corticostriatal network activity. Repeated KET model is characterized by schizophrenia-like symptomatology and alterations in glutamatergic and dopaminergic activity mainly in the PFC and the dorsomedial striatum (DMS), through a bi-directional pattern. These observations are accompanied by glutamatergic/GABAergic deviations paralleled to impaired function of parvalbumin- and cholecystokinin-positive interneurons, indicative of excitation/inhibition (E/I) imbalance. Moreover, CBD counteracted the schizophrenia-like behavioral phenotype as well as reverted prefrontal abnormalities and ventral hippocampal E/I deficits, while partially modulated dorsostriatal dysregulations. This study adds novel insights to our understanding of the KET-induced schizophrenia-related brain pathology, as well as the CBD antipsychotic action through a region-specific set of modulations in the corticohippocampal and costicostrtiatal circuitry of KET-induced profile contributing to the development of novel therapeutic strategies focused on the ECS and E/I imbalance restoration.

GABAergic and inflammatory changes in the frontal cortex following neonatal PCP plus isolation rearing, as a dual-hit neurodevelopmental model for schizophrenia

The pathogenesis of schizophrenia begins in early neurodevelopment and leads to excitatory-inhibitory imbalance. It is therefore essential that preclinical models used to understand disease, select drug targets and evaluate novel therapeutics encompass similar neurochemical deficits. One approach to improved preclinical modelling incorporates dual-hit neurodevelopmental insults, like neonatal administration of phencyclidine (PCP, to disrupt development of glutamatergic circuitry) then post-weaning isolation (Iso, to mimic adolescent social stress). We recently showed that male Lister-hooded rats exposed to PCP-Iso exhibit reduced hippocampal expression of the GABA interneuron marker calbindin. The current study expanded on this by investigating changes to additional populations of GABAergic interneurons in frontal cortical and hippocampal tissue from the same animals (by immunohistochemistry) as well as levels of GABA itself (via ELISA). Because inflammatory changes are also implicated in schizophrenia, we performed additional immunohistochemical evaluations of Iba-1 positive microglia as well as ELISA analysis of IL-6 in the same brain regions. Single-hit isolation-reared and dual-hit PCP-Iso rats both showed reduced parvalbumin immunoreactivity in the prelimbic/infralimbic region of the frontal cortex. However, this was more widespread in PCP-Iso, extending to the medial/ventral and lateral/dorsolateral orbitofrontal cortices. Loss of GABAergic markers was accompanied by increased microglial activation in the medial/ventral orbitofrontal cortices of PCP-Iso, together with frontal cortical IL-6 elevations not seen following single-hit isolation rearing. These findings enhance the face validity of PCP-Iso, and we advocate the use of this preclinical model for future evaluation of novel therapeutics-especially those designed to normalise excitatory-inhibitory imbalance or reduce neuroinflammation.

Perineuronal net density in schizophrenia: A systematic review of postmortem brain studies

BACKGROUND

The onset of schizophrenia is concurrent with multiple key processes of brain development, such as the maturation of inhibitory networks. Some of these processes are proposed to depend on the development of perineuronal nets (PNNs), a specialized extracellular matrix structure that surrounds preferentially parvalbumin-containing GABAergic interneurons (PVIs). PNNs are fundamental to the postnatal experience-dependent maturation of inhibitory brain circuits. PNN abnormalities have been proposed as a core pathophysiological finding in SCZ, being linked to widespread consequences on circuit disruptions underlying SCZ symptoms.

OBJECTIVE

Here, we systematically evaluate PNN density in postmortem brain studies of subjects with SCZ.

METHODS

A systematic search in 3 online databases (PubMed, Embase, and Scopus) and qualitative review analysis of case-control studies reporting on PNN density in the postmortem brain of subjects with SCZ were performed.

RESULTS

Results consisted of 7 studies that were included in the final analysis. The specific brain regions investigated in the studies varied, with most attention given to the dorsolateral prefrontal cortex (DLPFC; 3 studies) and amygdala (2 studies). Findings were mostly positive for reduced PNN density in SCZ, with 6 of the 7 studies reporting significant reductions and one reporting a tendency towards reduced PNN density. Overall, tissue processing methodologies were heterogeneous.

CONCLUSIONS

Despite few studies, PNN density was consistently reduced in SCZ across different brain regions. These findings support evidence that implicates deficits in PNN density in the pathophysiology of SCZ. However, more studies, preferably using similar methodological approaches as well as replication of findings, are needed.

Elevations in the Mitochondrial Matrix Protein Cyclophilin D Correlate With Reduced Parvalbumin Expression in the Prefrontal Cortex of Patients With Schizophrenia

BACKGROUND AND HYPOTHESIS

Cognitive deficits in schizophrenia are linked to dysfunctions of the dorsolateral prefrontal cortex (DLPFC), including alterations in parvalbumin (PV)-expressing interneurons (PVIs). Redox dysregulation and oxidative stress may represent convergence points in the pathology of schizophrenia, causing dysfunction of GABAergic interneurons and loss of PV. Here, we show that the mitochondrial matrix protein cyclophilin D (CypD), a critical initiator of the mitochondrial permeability transition pore (mPTP) and modulator of the intracellular redox state, is altered in PVIs in schizophrenia.

STUDY DESIGN

Western blotting was used to measure CypD protein levels in postmortem DLPFC specimens of schizophrenic patients (n = 27) and matched comparison subjects with no known history of psychiatric or neurological disorders (n = 26). In a subset of this cohort, multilabel immunofluorescent confocal microscopy with unbiased stereological sampling methods were used to quantify (1) numbers of PVI across the cortical mantle (20 unaffected comparison, 14 schizophrenia) and (2) PV and CypD protein levels from PVIs in the cortical layers 2-4 (23 unaffected comparison, 18 schizophrenia).

STUDY RESULTS

In schizophrenic patients, the overall number of PVIs in the DLPFC was not significantly altered, but in individual PVIs of layers 2-4 PV protein levels decreased along a superficial-to-deep gradient when compared to unaffected comparison subjects. These laminar-specific PVI alterations were reciprocally linked to significant CypD elevations both in PVIs and total DLPFC gray matter.

CONCLUSIONS

Our findings support previously reported PVI anomalies in schizophrenia and suggest that CypD-mediated mPTP formation could be a potential contributor to PVI dysfunction in schizophrenia.

Prefrontal Excitation/ Inhibition Balance Supports Adolescent Enhancements in Circuit Signal to Noise Ratio

The development and refinement of neuronal circuitry allow for stabilized and efficient neural recruitment, supporting adult-like behavioral performance. During adolescence, the maturation of PFC is proposed to be a critical period (CP) for executive function, driven by a break in balance between glutamatergic excitation and GABAergic inhibition (E/I) neurotransmission. During CPs, cortical circuitry fine-tunes to improve information processing and reliable responses to stimuli, shifting from spontaneous to evoked activity, enhancing the SNR, and promoting neural synchronization. Harnessing 7T MR spectroscopy and EEG in a longitudinal cohort (N = 164, ages 10-32 years, 283 neuroimaging sessions), we outline associations between age-related changes in glutamate and GABA neurotransmitters and EEG measures of cortical SNR. We find developmental decreases in spontaneous activity and increases in cortical SNR during our auditory steady state task using 40 Hz stimuli. Decreases in spontaneous activity were associated with glutamate levels in DLPFC, while increases in cortical SNR were associated with more balanced Glu and GABA levels. These changes were associated with improvements in working memory performance. This study provides evidence of CP plasticity in the human PFC during adolescence, leading to stabilized circuitry that allows for the optimal recruitment and integration of multisensory input, resulting in improved executive function.

Imaging high-frequency voltage dynamics in multiple neuron classes of behaving mammals

Fluorescent genetically encoded voltage indicators report transmembrane potentials of targeted cell-types. However, voltage-imaging instrumentation has lacked the sensitivity to track spontaneous or evoked high-frequency voltage oscillations in neural populations. Here we describe two complementary TEMPO voltage-sensing technologies that capture neural oscillations up to ~100 Hz. Fiber-optic TEMPO achieves ~10-fold greater sensitivity than prior photometry systems, allows hour-long recordings, and monitors two neuron-classes per fiber-optic probe in freely moving mice. With it, we uncovered cross-frequency-coupled theta- and gamma-range oscillations and characterized excitatory-inhibitory neural dynamics during hippocampal ripples and visual cortical processing. The TEMPO mesoscope images voltage activity in two cell-classes across a ~8-mm-wide field-of-view in head-fixed animals. In awake mice, it revealed sensory-evoked excitatory-inhibitory neural interactions and traveling gamma and 3-7 Hz waves in the visual cortex, and previously unreported propagation directions for hippocampal theta and beta waves. These technologies have widespread applications probing diverse oscillations and neuron-type interactions in healthy and diseased brains.

Glyphosate-based herbicide exposure affects cognitive flexibility and social cognition in adult mice

Glyphosate (Gly) is the active ingredient of several widely used herbicide formulations. Studies on Gly and glyphosate-based herbicide (GBH) exposure in different experimental models have suggested that the nervous system represented a key target for its toxicity, especially the prefrontal cortex (PFC). However, it is still unknown whether exposure to GBH affects higher brain functions dependent on PFC circuitry. The present work aimed to examine the effects of subtoxic doses of GBH on social cognition and cognitive flexibility as two functions belonging to higher brain function in mice. To do so, adult male mice were exposed daily to GBH by gavage at doses of 250 or 500 mg/kg for a sub-chronic period lasting 6 weeks. Then, mice were subjected to behavioral testing using the three-chamber and the Barnes maze paradigms. Our results indicate that GBH did not affect sociability. However, we found that GBH affects social cognition expressed by a lower discrimination index in the three-chamber test. Moreover, spatial memories evaluated during the probe trial, and cognitive flexibility evaluated during the reversal probe, were affected in mice exposed to GBH. Based on these results, exposure to subtoxic doses of GBH led to neurobehavioral alterations affecting the integrity of social cognition and cognitive flexibility functions. Finally, these data urge a thorough investigation of the cellular and molecular mechanisms underlying these alterations.

Molecular and cellular rhythms in excitatory and inhibitory neurons in the mouse prefrontal cortex

Previous studies have shown that there are rhythms in gene expression in the mouse prefrontal cortex (PFC); however, the contribution of different cell types and potential variation by sex has not yet been determined. Of particular interest are excitatory pyramidal cells and inhibitory parvalbumin (PV) interneurons, as interactions between these cell types are essential for regulating the excitation/inhibition balance and controlling many of the cognitive functions regulated by the PFC. In this study, we identify cell-type specific rhythms in the translatome of PV and pyramidal cells in the mouse PFC and assess diurnal rhythms in PV cell electrophysiological properties. We find that while core molecular clock genes are conserved and synchronized between cell types, pyramidal cells have nearly twice as many rhythmic transcripts as PV cells (35% vs. 18%). Rhythmic transcripts in pyramidal cells also show a high degree of overlap between sexes, both in terms of which transcripts are rhythmic and in the biological processes associated with them. Conversely, in PV cells, rhythmic transcripts from males and females are largely distinct. Moreover, we find sex-specific effects of phase on action potential properties in PV cells that are eliminated by environmental circadian disruption. Together, this study demonstrates that rhythms in gene expression and electrophysiological properties in the mouse PFC vary by both cell type and sex. Moreover, the biological processes associated with these rhythmic transcripts may provide insight into the unique functions of rhythms in these cells, as well as their selective vulnerabilities to circadian disruption.

Reduced excitatory activity in the developing mPFC mediates a PVH-to-PVL transition and impaired social cognition in autism spectrum disorders

Understanding the neuropathogenesis of impaired social cognition in autism spectrum disorders (ASD) is challenging. Altered cortical parvalbumin-positive (PV+) interneurons have been consistently observed in ASD, but their roles and the underlying mechanisms remain poorly understood. In our study, we observed a downward-shifted spectrum of PV expression in the developing medial prefrontal cortex (mPFC) of ASD mouse models due to decreased activity of PV+ neurons. Surprisingly, chemogenetically suppressing PV+ neuron activity during postnatal development failed to induce ASD-like behaviors. In contrast, lowering excitatory activity in the developing mPFC not only dampened the activity state and PV expression of individual PV+ neurons, but also replicated ASD-like social deficits. Furthermore, enhancing excitation, but not PV+ interneuron-mediated inhibition, rescued social deficits in ASD mouse models. Collectively, our findings propose that reduced excitatory activity in the developing mPFC may serve as a shared local circuitry mechanism triggering alterations in PV+ interneurons and mediating impaired social functions in ASD.

Sub-concussive head impacts from heading footballs do not acutely alter brain excitability as compared to a control group

BACKGROUND

Repeated sub-concussive head impacts are a growing brain health concern, but their possible biomarkers remain elusive. One impediment is the lack of a randomised controlled human experimental model to study their effects on the human brain.

OBJECTIVES

This work had two objectives. The first one was to provide a randomised controlled human experimental model to study the acute effects of head impacts on brain functions. To achieve this, this work's second objective was to investigate if head impacts from heading footballs acutely alter brain excitability by increasing corticospinal inhibition as compared to a control group.

METHODS

In practised and unpractised young healthy adults, transcranial magnetic stimulation was used to assess corticospinal silent period (CSP) duration and corticospinal excitability (CSE) before and immediately after performing headings by returning 20 hand-thrown balls directed to the head (Headings; n = 30) or the dominant foot (Control; n = 30). Moreover, the Rivermead Post-Concussion Questionnaire (RPQ) was used to assess the symptoms of head impacts. Head acceleration was also assessed in subgroups of participants.

RESULTS

The intervention lengthened CSP duration in both the Headings (6.4 ± 7.5%) and Control groups (4.6 ± 2.6%), with no difference in lengthening between the two groups. Moreover, CSE was not altered by the intervention and did not differ between groups. However, performing headings increased headaches and dizziness symptoms and resulted in greater head acceleration upon each football throw (12.5 ± 1.9g) as compared to the control intervention (5.5 ± 1.3g).

CONCLUSIONS

The results suggest that head impacts from football headings do not acutely alter brain excitability as compared to a control intervention. However, the results also suggest that the present protocol can be used as an experimental model to investigate the acute effects of head impacts on the human brain.

GABA system in the prefrontal cortex involved in psychostimulant addiction

Drug addiction is a chronic and relapse brain disorder. Psychostimulants such as cocaine and amphetamine are highly addictive drugs. Abuse drugs target various brain areas in the nervous system. Recent studies have shown that the prefrontal cortex (PFC) plays a key role in regulating addictive behaviors. The PFC is made up of excitatory glutamatergic cells and gamma-aminobutyric acid (GABAergic) interneurons. Recently, studies showed that GABA level was related with psychostimulant addiction. In this review, we will introduce the role and mechanism of GABA and γ-aminobutyric acid receptors (GABARs) of the PFC in regulating drug addiction, especially in psychostimulant addiction.

The Neuroprotective Effect of Neural Cell Adhesion Molecule L1 in the Hippocampus of Aged Alzheimer's Disease Model Mice

Alzheimer's disease (AD) is a severe neurodegenerative disorder and the most common form of dementia, causing the loss of cognitive function. Our previous study has shown, using a doubly mutated mouse model of AD (APP/PS1), that the neural adhesion molecule L1 directly binds amyloid peptides and decreases plaque load and gliosis when injected as an adeno-associated virus construct (AAV-L1) into APP/PS1 mice. In this study, we microinjected AAV-L1, using a Hamilton syringe, directly into the 3-month-old APP/PS1 mouse hippocampus and waited for a year until significant neurodegeneration developed. We stereologically counted the principal neurons and parvalbumin-positive interneurons in the hippocampus, estimated the density of inhibitory synapses around principal cells, and compared the AAV-L1 injection models with control injections of green fluorescent protein (AAV-GFP) and the wild-type hippocampus. Our results show that there is a significant loss of granule cells in the dentate gyrus of the APP/PS1 mice, which was improved by AAV-L1 injection, compared with the AAV-GFP controls (p < 0.05). There is also a generalized loss of parvalbumin-positive interneurons in the hippocampus of APP/PS1 mice, which is ameliorated by AAV-L1 injection, compared with the AAV-GFP controls (p < 0.05). Additionally, AAV-L1 injection promotes the survival of inhibitory synapses around the principal cells compared with AAV-GFP controls in all three hippocampal subfields (p < 0.01). Our results indicate that L1 promotes neuronal survival and protects the synapses in an AD mouse model, which could have therapeutic implications.

Chronic Stress Alters Synaptic Inhibition/Excitation Balance of Pyramidal Neurons But Not PV Interneurons in the Infralimbic and Prelimbic Cortices of C57BL/6J Mice

The medial prefrontal cortex (mPFC) plays a pivotal role in regulating working memory, executive function, and self-regulatory behaviors. Dysfunction in the mPFC circuits is a characteristic feature of several neuropsychiatric disorders including schizophrenia, depression, and post-traumatic stress disorder. Chronic stress (CS) is widely recognized as a major triggering factor for the onset of these disorders. Although evidence suggests synaptic dysfunction in mPFC circuits following CS exposure, it remains unclear how different neuronal populations in the infralimbic (IL) and prelimbic (PL) cortices are affected in terms of synaptic inhibition/excitation balance (I/E ratio). Here, using neuroproteomic analysis and whole-cell patch-clamp recordings in pyramidal neurons (PNs) and parvalbumin (PV) interneurons within the PL and IL cortices, we examined the synaptic changes after 21 d of chronic unpredictable stress, in male mice. Our results reveal distinct impacts of CS on PL and IL PNs, resulting in an increased I/E ratio in both subregions but through different mechanisms: CS increases inhibitory synaptic drive in the PL while decreasing excitatory synaptic drive in the IL. Notably, the I/E ratio and excitatory and inhibitory synaptic drive of PV interneurons remained unaffected in both PL and IL circuits following CS exposure. These findings offer novel mechanistic insights into the influence of CS on mPFC circuits and support the hypothesis of stress-induced mPFC hypofunction.

Effects of adolescent intermittent ethanol exposure on cortical perineuronal net and parvalbumin expression in adulthood mediate behavioral inflexibility

BACKGROUND

Alcohol is commonly consumed by adolescents in a binge-like pattern, which can lead to long-lasting cognitive deficits, including reduced behavioral flexibility. We and others have determined that adolescent intermittent ethanol (AIE) exposure leads to increased number of perineuronal net (PNN) numbers in brain regions that are important for behavioral flexibility. However, whether altered neurochemistry stemming from AIE exposure plays a significant role in reduced behavioral flexibility is unknown.

METHODS

We measured the number and size of parvalbumin expressing (PV+) interneurons and associated PNNs within the orbitofrontal cortex (OFC), prelimbic cortex (PrL), infralimbic cortex (IL), and anterior insular cortex (AIC) of female and male rats following AIE or control exposure and subsequent training on an attentional set-shift task (ASST). We then ran analyses to determine whether AIE-induced changes in PV and PNN measures statistically mediated the AIE-induced behavioral deficit in reversal learning.

RESULTS

We demonstrate that AIE exposure impaired behavioral flexibility on reversal two of the ASST (i.e., recalling the initial learned associations), and led to smaller PV+ cells and increased PNN numbers in the AIC. Interestingly, PNN size and number were not altered in the PrL or IL following AIE exposure, in contrast to prior reports. Mediation analyses suggest that AIE alters behavioral flexibility, at least in part through changes in PV and PNN fluorescent measures in the AIC.

CONCLUSIONS

This study reveals a significant link between AIE exposure, neural alterations, and diminished behavioral flexibility in rats, and highlights a potential novel mechanism comprising changes in PV and PNN measures within the AIC. Future studies should explore the impact of PNN degradation within the AIC on behavioral flexibility.

Gephyrin phosphorylation facilitates sexually dimorphic development and function of parvalbumin interneurons in the mouse hippocampus

The precise function of specialized GABAergic interneuron subtypes is required to provide appropriate synaptic inhibition for regulating principal neuron excitability and synchronization within brain circuits. Of these, parvalbumin-type (PV neuron) dysfunction is a feature of several sex-biased psychiatric and brain disorders, although, the underlying developmental mechanisms are unclear. While the transcriptional action of sex hormones generates sexual dimorphism during brain development, whether kinase signaling contributes to sex differences in PV neuron function remains unexplored. In the hippocampus, we report that gephyrin, the main inhibitory post-synaptic scaffolding protein, is phosphorylated at serine S268 and S270 in a developmentally-dependent manner in both males and females. When examining GphnS268A/S270A mice in which site-specific phosphorylation is constitutively blocked, we found that sex differences in PV neuron density in the hippocampal CA1 present in WT mice were abolished, coincident with a female-specific increase in PV neuron-derived terminals and increased inhibitory input onto principal cells. Electrophysiological analysis of CA1 PV neurons indicated that gephyrin phosphorylation is required for sexually dimorphic function. Moreover, while male and female WT mice showed no difference in hippocampus-dependent memory tasks, GphnS268A/S270A mice exhibited sex- and task-specific deficits, indicating that gephyrin phosphorylation is differentially required by males and females for convergent cognitive function. In fate mapping experiments, we uncovered that gephyrin phosphorylation at S268 and S270 establishes sex differences in putative PV neuron density during early postnatal development. Furthermore, patch-sequencing of putative PV neurons at postnatal day 4 revealed that gephyrin phosphorylation contributes to sex differences in the transcriptomic profile of developing interneurons. Therefore, these early shifts in male-female interneuron development may drive adult sex differences in PV neuron function and connectivity. Our results identify gephyrin phosphorylation as a new substrate organizing PV neuron development at the anatomical, functional, and transcriptional levels in a sex-dependent manner, thus implicating kinase signaling disruption as a new mechanism contributing to the sex-dependent etiology of brain disorders.

Genetic approaches to elucidating cortical and hippocampal GABAergic interneuron diversity

GABAergic interneurons (INs) in the mammalian forebrain represent a diverse population of cells that provide specialized forms of local inhibition to regulate neural circuit activity. Over the last few decades, the development of a palette of genetic tools along with the generation of single-cell transcriptomic data has begun to reveal the molecular basis of IN diversity, thereby providing deep insights into how different IN subtypes function in the forebrain. In this review, we outline the emerging picture of cortical and hippocampal IN speciation as defined by transcriptomics and developmental origin and summarize the genetic strategies that have been utilized to target specific IN subtypes, along with the technical considerations inherent to each approach. Collectively, these methods have greatly facilitated our understanding of how IN subtypes regulate forebrain circuitry via cell type and compartment-specific inhibition and thus have illuminated a path toward potential therapeutic interventions for a variety of neurocognitive disorders.

Prefrontal Regulation of Social Behavior and Related Deficits: Insights From Rodent Studies

The prefrontal cortex (PFC) is well known as the executive center of the brain, combining internal states and goals to execute purposeful behavior, including social actions. With the advancement of tools for monitoring and manipulating neural activity in rodents, substantial progress has been made in understanding the specific cell types and neural circuits within the PFC that are essential for processing social cues and influencing social behaviors. Furthermore, combining these tools with translationally relevant behavioral paradigms has also provided novel insights into the PFC neural mechanisms that may contribute to social deficits in various psychiatric disorders. This review highlights findings from the past decade that have shed light on the PFC cell types and neural circuits that support social information processing and distinct aspects of social behavior, including social interactions, social memory, and social dominance. We also explore how the PFC contributes to social deficits in rodents induced by social isolation, social fear conditioning, and social status loss. These studies provide evidence that the PFC uses both overlapping and unique neural mechanisms to support distinct components of social cognition. Furthermore, specific PFC neural mechanisms drive social deficits induced by different contexts.

The impact of the mesoprefrontal dopaminergic system on the maturation of interneurons in the murine prefrontal cortex

The prefrontal cortex (PFC) undergoes a protracted maturation process. This is true both for local interneurons and for innervation from midbrain dopaminergic (mDA) neurons. In the striatum, dopaminergic (DA) neurotransmission is required for the maturation of medium spiny neurons during a critical developmental period. To investigate whether DA innervation influences the maturation of interneurons in the PFC, we used a conditional knockout (cKO) mouse model in which innervation from mDA neurons to the mPFC (mesoprefrontal innnervation) is not established during development. In this mouse model, the maturation of parvalbumin (PV) and calbindin (CB) interneuron populations in the PFC is dysregulated during a critical period in adolescence with changes persisting into adulthood. PV interneurons are particularly vulnerable to lack of mesoprefrontal input, showing an inability to maintain adequate PV expression with a concomitant decrease in Gad1 expression levels. Interestingly, lack of mesoprefrontal innervation does not appear to induce compensatory changes such as upregulation of DA receptor expression in PFC neurons or increased innervation density of other neuromodulatory (serotonergic and noradrenergic) innervation. In conclusion, our study shows that adolescence is a sensitive period during which mesoprefrontal input plays a critical role in promoting the maturation of specific interneuron subgroups. The results of this study will help to understand how a dysregulated mesoprefrontal DA system contributes to the pathophysiology of neurodevelopmental disorders.

Parvalbumin gates chronic pain through the modulation of firing patterns in inhibitory neurons

Spinal cord dorsal horn inhibition is critical to the processing of sensory inputs, and its impairment leads to mechanical allodynia. How this decreased inhibition occurs and whether its restoration alleviates allodynic pain are poorly understood. Here, we show that a critical step in the loss of inhibitory tone is the change in the firing pattern of inhibitory parvalbumin (PV)-expressing neurons (PVNs). Our results show that PV, a calcium-binding protein, controls the firing activity of PVNs by enabling them to sustain high-frequency tonic firing patterns. Upon nerve injury, PVNs transition to adaptive firing and decrease their PV expression. Interestingly, decreased PV is necessary and sufficient for the development of mechanical allodynia and the transition of PVNs to adaptive firing. This transition of the firing pattern is due to the recruitment of calcium-activated potassium (SK) channels, and blocking them during chronic pain restores normal tonic firing and alleviates chronic pain. Our findings indicate that PV is essential for controlling the firing pattern of PVNs and for preventing allodynia. Developing approaches to manipulate these mechanisms may lead to different strategies for chronic pain relief.

Sex-specific biphasic alpha-synuclein response and alterations of interneurons in a COVID-19 hamster model

BACKGROUND

Coronavirus disease 2019 (COVID-19) frequently leads to neurological complications after recovery from acute infection, with higher prevalence in women. However, mechanisms by which SARS-CoV-2 disrupts brain function remain unclear and treatment strategies are lacking. We previously demonstrated neuroinflammation in the olfactory bulb of intranasally infected hamsters, followed by alpha-synuclein and tau accumulation in cortex, thus mirroring pathogenesis of neurodegenerative diseases such as Parkinson's or Alzheimer's disease.

METHODS

To uncover the sex-specific spatiotemporal profiles of neuroinflammation and neuronal dysfunction following intranasal SARS-CoV-2 infection, we quantified microglia cell density, alpha-synuclein immunoreactivity and inhibitory interneurons in cortical regions, limbic system and basal ganglia at acute and late post-recovery time points.

FINDINGS

Unexpectedly, microglia cell density and alpha-synuclein immunoreactivity decreased at 6 days post-infection, then rebounded to overt accumulation at 21 days post-infection. This biphasic response was most pronounced in amygdala and striatum, regions affected early in Parkinson's disease. Several brain regions showed altered densities of parvalbumin and calretinin interneurons which are involved in cognition and motor control. Of note, females appeared more affected.

INTERPRETATION

Our results demonstrate that SARS-CoV-2 profoundly disrupts brain homeostasis without neuroinvasion, via neuroinflammatory and protein regulation mechanisms that persist beyond viral clearance. The regional patterns and sex differences are in line with neurological deficits observed after SARS-CoV-2 infection.

FUNDING

Federal Ministry of Health, Germany (BMG; ZMV I 1-2520COR501 to G.G.), Federal Ministry of Education and Research, Germany (BMBF; 03COV06B to G.G.), Ministry of Science and Culture of Lower Saxony in Germany (14-76403-184, to G.G. and F.R.).

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.

Inter and intralaminar excitation of parvalbumin interneurons in mouse barrel cortex

Parvalbumin (PV) interneurons are inhibitory fast-spiking cells with essential roles in directing the flow of information through cortical circuits. These neurons set the balance between excitation and inhibition and control rhythmic activity. PV interneurons differ between cortical layers in their morphology, circuitry, and function, but how their electrophysiological properties vary has received little attention. Here we investigate responses of PV interneurons in different layers of primary somatosensory barrel cortex (BC) to different excitatory inputs. With the genetically-encoded hybrid voltage sensor, hVOS, we recorded voltage changes in many L2/3 and L4 PV interneurons simultaneously, with stimulation applied to either L2/3 or L4. A semi-automated procedure was developed to identify small regions of interest corresponding to single responsive PV interneurons. Amplitude, half-width, and rise-time were greater for PV interneurons residing in L2/3 compared to L4. Stimulation in L2/3 elicited responses in both L2/3 and L4 with longer latency compared to stimulation in L4. These differences in latency between layers could influence their windows for temporal integration. Thus, PV interneurons in different cortical layers of BC respond in a layer specific and input specific manner, and these differences have potential roles in cortical computations.

Vibration-reduced anxiety-like behavior relies on ameliorating abnormalities of the somatosensory cortex and medial prefrontal cortex

Tibetan singing bowls emit low-frequency sounds and produce perceptible harmonic tones and vibrations through manual tapping. The sounds the singing bowls produce have been shown to enhance relaxation and reduce anxiety. However, the underlying mechanism remains unclear. In this study, we used chronic restraint stress or sleep deprivation to establish mouse models of anxiety that exhibit anxiety-like behaviors. We then supplied treatment with singing bowls in a bottomless cage placed on the top of a cushion. We found that unlike in humans, the combination of harmonic tones and vibrations did not improve anxiety-like behaviors in mice, while individual vibration components did. Additionally, the vibration of singing bowls increased the level of N-methyl-D-aspartate receptor 1 in the somatosensory cortex and prefrontal cortex of the mice, decreased the level of γ-aminobutyric acid A (GABA) receptor α 1 subtype, reduced the level of CaMKII in the prefrontal cortex, and increased the number of GABAergic interneurons. At the same time, electrophysiological tests showed that the vibration of singing bowls significantly reduced the abnormal low-frequency gamma oscillation peak frequency in the medial prefrontal cortex caused by stress restraint pressure and sleep deprivation. Results from this study indicate that the vibration of singing bowls can alleviate anxiety-like behaviors by reducing abnormal molecular and electrophysiological events in somatosensory and medial prefrontal cortex.

The relationship between gamma-band neural oscillations and language skills in youth with Autism Spectrum Disorder and their first-degree relatives

BACKGROUND

Most children with Autism Spectrum Disorder (ASD) have co-occurring language impairments and some of these autism-specific language difficulties are also present in their non-autistic first-degree relatives. One of the possible neural mechanisms associated with variability in language functioning is alterations in cortical gamma-band oscillations, hypothesized to be related to neural excitation and inhibition balance.

METHODS

We used a high-density 128-channel electroencephalography (EEG) to register brain response to speech stimuli in a large sex-balanced sample of participants: 125 youth with ASD, 121 typically developing (TD) youth, and 40 unaffected siblings (US) of youth with ASD. Language skills were assessed with Clinical Evaluation of Language Fundamentals.

RESULTS

First, during speech processing, we identified significantly elevated gamma power in ASD participants compared to TD controls. Second, across all youth, higher gamma power was associated with lower language skills. Finally, the US group demonstrated an intermediate profile in both language and gamma power, with nonverbal IQ mediating the relationship between gamma power and language skills.

LIMITATIONS

We only focused on one of the possible neural contributors to variability in language functioning. Also, the US group consisted of a smaller number of participants in comparison to the ASD or TD groups. Finally, due to the timing issue in EEG system we have provided only non-phase-locked analysis.

CONCLUSIONS

Autistic youth showed elevated gamma power, suggesting higher excitation in the brain in response to speech stimuli and elevated gamma power was related to lower language skills. The US group showed an intermediate pattern of gamma activity, suggesting that the broader autism phenotype extends to neural profiles.

Parvalbumin interneurons in human ventromedial prefrontal cortex: a comprehensive post-mortem study of myelination and perineuronal nets in neurotypical individuals and depressed suicides with and without a history of child abuse

Cortical parvalbumin interneurons (PV+) are major regulators of excitatory/inhibitory information processing, and their maturation is associated with the opening of developmental critical periods (CP). Recent studies reveal that cortical PV+ axons are myelinated, and that myelination along with perineuronal net (PNN) maturation around PV+ cells is associated with the closures of CP. Although PV+ interneurons are susceptible to early-life stress, their relationship between their myelination and PNN coverage remains unexplored. This study compared the fine features of PV+ interneurons in well-characterized human post-mortem ventromedial prefrontal cortex samples (n = 31) from depressed suicides with or without a history of child abuse (CA) and matched controls. In healthy controls, 81% of all sampled PV+ interneurons displayed a myelinated axon, while a subset (66%) of these cells also displayed a PNN, proposing a relationship between both attributes. Intriguingly, a 3-fold increase in the proportion of unmyelinated PV+ interneurons with a PNN was observed in CA victims, along with greater PV-immunofluorescence intensity in myelinated PV+ cells with a PNN. This study, which is the first to provide normative data on myelination and PNNs around PV+ interneurons in human neocortex, sheds further light on the cellular and molecular consequences of early-life adversity on cortical PV+ interneurons.

The relationship between the gut microbiota and oxidative stress in the cognitive function of schizophrenia: A pilot study in China

Cognitive impairment is a core symptom of schizophrenia. The gut microbiota (GM) and oxidative stress may play important roles in the pathophysiological mechanisms of cognitive impairment. This study aimed to explore the relationship between GM and oxidative stress in the cognitive function of schizophrenia. GM obtained by 16S RNA sequencing and serum superoxide dismutase (SOD) levels from schizophrenia patients (N = 68) and healthy controls (HCs, N = 72) were analyzed. All psychiatric symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). Cognitive function was assessed using the MATRICS Consensus Cognitive Battery (MCCB). Correlation analysis was used to explore the relationship between GM, SOD, and cognitive function. Machine learning models were used to identify potential biomarkers. Compared to HCs, the relative abundances of Collinsella, undefined Ruminococcus, Lactobacillus, Eubacterium, Mogibacterium, Desulfovibrio, Bulleidia, Succinivibrio, Corynebacterium, and Atopobium were higher in patients with schizophrenia, but Faecalibacterium, Anaerostipes, Turicibacter, and Ruminococcus were lower. In patients with schizophrenia, the positive factor, general factor, and total score of MCCB positively correlated with Lactobacillus, Collinsella, and Lactobacillus, respectively; SOD negatively correlated with Eubacterium, Collinsella, Lactobacillus, Corynebacterium, Bulleidia, Mogibacterium, and Succinivibrio, but positively correlated with Faecalibacterium, Ruminococcus, and MCCB verbal learning index scores; Faecalibacterium and Turicibacter were positively correlated with MCCB visual learning index scores and speed of processing index scores, respectively. Our findings revealed a correlation between SOD and GM and confirmed that cognitive dysfunction in patients with schizophrenia involves abnormal SOD levels and GM changes.

Epidermal Growth Factor Suppresses the Development of GABAergic Neurons Via the Modulation of Perineuronal Net Formation in the Neocortex of Developing Rodent Brains

Previously, we reported that epidermal growth factor (EGF) suppresses GABAergic neuronal development in the rodent cortex. Parvalbumin-positive GABAergic neurons (PV neurons) have a unique extracellular structure, perineuronal nets (PNNs). PNNs are formed during the development of PV neurons and are mainly formed from chondroitin sulfate (CS) proteoglycans (CSPGs). We examined the effect of EGF on CSPG production and PNN formation as a potential molecular mechanism for the inhibition of inhibiting GABAergic neuronal development by EGF. In EGF-overexpressing transgenic (EGF-Tg) mice, the number of PNN-positive PV neurons was decreased in the cortex compared with that in wild-type mice, as in our previous report. The amount of CS and neurocan was also lower in the cortex of EGF-Tg mice, with a similar decrease observed in EGF-treated cultured cortical neurons. PD153035, an EGF receptor (ErbB1) kinase inhibitor, prevented those mentioned above excess EGF-induced reduction in PNN. We explored the molecular mechanism underlying the effect of EGF on PNNs using fluorescent substrates for matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinases (ADAMs). EGF increased the enzyme activity of MMPs and ADAMs in cultured neurons. These enzyme activities were also increased in the EGF-Tg mice cortex. GM6001, a broad inhibitor of MMPs and ADAMs, also blocked EGF-induced PNN reductions. Therefore, EGF/EGF receptor signals may regulate PNN formation in the developing cortex.

Spike-induced cytoarchitectonic changes in epileptic human cortex are reduced via MAP2K inhibition

Interictal spikes are electroencephalographic discharges that occur at or near brain regions that produce epileptic seizures. While their role in generating seizures is not well understood, spikes have profound effects on cognition and behaviour, depending on where and when they occur. We previously demonstrated that spiking areas of human neocortex show sustained MAPK activation in superficial cortical Layers I-III and are associated with microlesions in deeper cortical areas characterized by reduced neuronal nuclear protein staining and increased microglial infiltration. Based on these findings, we chose to investigate additional neuronal populations within microlesions, specifically inhibitory interneurons. Additionally, we hypothesized that spiking would be sufficient to induce similar cytoarchitectonic changes within the rat cortex and that inhibition of MAPK signalling, using a MAP2K inhibitor, would not only inhibit spike formation but also reduce these cytoarchitectonic changes and improve behavioural outcomes. To test these hypotheses, we analysed tissue samples from 16 patients with intractable epilepsy who required cortical resections. We also utilized a tetanus toxin-induced animal model of interictal spiking, designed to produce spikes without seizures in male Sprague-Dawley rats. Rats were fitted with epidural electrodes, to permit EEG recording for the duration of the study, and automated algorithms were implemented to quantify spikes. After 6 months, animals were sacrificed to assess the effects of chronic spiking on cortical cytoarchitecture. Here, we show that microlesions may promote excitability due to a significant reduction of inhibitory neurons that could be responsible for promoting interictal spikes in superficial layers. Similarly, we found that the induction of epileptic spikes in the rat model produced analogous changes, including reduced neuronal nuclear protein, calbindin and parvalbumin-positive neurons and increased microglia, suggesting that spikes are sufficient for inducing these cytoarchitectonic changes in humans. Finally, we implicated MAPK signalling as a driving force producing these pathological changes. Using CI-1040 to inhibit MAP2K, both acutely and after spikes developed, resulting in fewer interictal spikes, reduced microglial activation and less inhibitory neuron loss. Treated animals had significantly fewer high-amplitude, short-duration spikes, which correlated with improved spatial memory performance on the Barnes maze. Together, our results provide evidence for a cytoarchitectonic pathogenesis underlying epileptic cortex, which can be ameliorated through both early and delayed MAP2K inhibition. These findings highlight the potential role for CI-1040 as a pharmacological treatment that could prevent the development of epileptic activity and reduce cognitive impairment in both patients with epilepsy and those with non-epileptic spike-associated neurobehavioural disorders.

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.

GABAergic interneuron diversity and organization are crucial for the generation of human-specific functional neural networks in cerebral organoids

This mini review investigates the importance of GABAergic interneurons for the network function of human-induced pluripotent stem cells (hiPSC)-derived brain organoids. The presented evidence suggests that the abundance, diversity and three-dimensional cortical organization of GABAergic interneurons are the primary elements responsible for the creation of synchronous neuronal firing patterns. Without intricate inhibition, coupled oscillatory patterns cannot reach a sufficient complexity to transfer spatiotemporal information constituting physiological network function. Furthermore, human-specific brain network function seems to be mediated by a more complex and interconnected inhibitory structure that remains developmentally flexible for a longer period when compared to rodents. This suggests that several characteristics of human brain networks cannot be captured by rodent models, emphasizing the need for model systems like organoids that adequately mimic physiological human brain function in vitro.

Sexual differences in neuronal and synaptic properties across subregions of the mouse insular cortex

BACKGROUND

The insular cortex (IC) plays a pivotal role in processing interoceptive and emotional information, offering insights into sex differences in behavior and cognition. The IC comprises two distinct subregions: the anterior insular cortex (aIC), that processes emotional and social signals, and the posterior insular cortex (pIC), specialized in interoception and perception of pain. Pyramidal projection neurons within the IC integrate multimodal sensory inputs, influencing behavior and cognition. Despite previous research focusing on neuronal connectivity and transcriptomics, there has been a gap in understanding pyramidal neurons characteristics across subregions and between sexes.

METHODS

Adult male and female C57Bl/6J mice were sacrificed and tissue containing the IC was collected for ex vivo slice electrophysiology recordings that examined baseline sex differences in synaptic plasticity and transmission within aIC and pIC subregions.

RESULTS

Clear differences emerged between aIC and pIC neurons in both males and females: aIC neurons exhibited distinctive features such as larger size, increased hyperpolarization, and a higher rheobase compared to their pIC counterparts. Furthermore, we observed variations in neuronal excitability linked to sex, with male pIC neurons displaying a greater level of excitability than their female counterparts. We also identified region-specific differences in excitatory and inhibitory synaptic activity and the balance between excitation and inhibition in both male and female mice. Adult females demonstrated greater synaptic strength and maximum response in the aIC compared to the pIC. Lastly, synaptic long-term potentiation occurred in both subregions in males but was specific to the aIC in females.

CONCLUSIONS

We conclude that there are sex differences in synaptic plasticity and excitatory transmission in IC subregions, and that distinct properties of IC pyramidal neurons between sexes could contribute to differences in behavior and cognition between males and females.

Parvalbumin interneuron deficiency in the prefrontal and motor cortices of spontaneously hypertensive rats: an attention-deficit hyperactivity disorder animal model insight

Background

Attention deficit hyperactivity disorder (ADHD) is characterized by impairments in developmental-behavioral inhibition, resulting in impulsivity and hyperactivity. Recent research has underscored cortical inhibition deficiencies in ADHD via the gamma-aminobutyric acid (GABA)ergic system, which is crucial for maintaining excitatory-inhibitory balance in the brain. This study explored postnatal changes in parvalbumin (PV) immunoreactivity, indicating GABAergic interneuron types, in the prefrontal (PFC) and motor (MC) cortices of spontaneously hypertensive rats (SHRs), an ADHD animal model.

Methods

Examining PV- positive (PV+) cells associated with dopamine D2 receptors (D2) and the impact of dopamine on GABA synthesis, we also investigated changes in the immunoreactivity of D2 and tyrosine hydroxylase (TH). Brain sections from 4- to 10-week-old SHRs and Wistar Kyoto rats (WKYs) were immunohistochemically analyzed, comparing PV+, D2+ cells, and TH+ fiber densities across age-matched SHRs and WKYs in specific PFC/MC regions.

Results

The results revealed significantly reduced PV+ cell density in SHRs: prelimbic (~20% less), anterior cingulate (~15% less), primary (~15% less), and secondary motor (~17% less) cortices. PV+ deficits coincided with the upregulation of D2 in prepubertal SHRs and the downregulation of TH predominantly in pubertal/postpubertal SHRs.

Conclusion

Reduced PV+ cells in various PFC regions could contribute to inattention/behavioral alterations in ADHD, while MC deficits could manifest as motor hyperactivity. D2 upregulation and TH deficits may impact GABA synthesis, exacerbating behavioral deficits in ADHD. These findings not only shed new light on ADHD pathophysiology but also pave the way for future research endeavors.

Choice impulsivity after repeated social stress is associated with increased perineuronal nets in the medial prefrontal cortex

Repeated stress can predispose to substance abuse. However, behavioral and neurobiological adaptations that link stress to substance abuse remain unclear. This study investigates whether intermittent social defeat (ISD), a stress protocol that promotes drug-seeking behavior, alters intertemporal decision-making and cortical inhibitory function in the medial prefrontal cortex (mPFC). Male long evans rats were trained in a delay discounting task (DDT) where rats make a choice between a fast (1 s) small reward (1 sugar pellet) and a large reward (3 sugar pellets) that comes with a time delay (10 s or 20 s). A decreased preference for delayed rewards was used as an index of choice impulsivity. Rats were exposed to ISD and tested in the DDT 24 h after each stress episode, and one- and two-weeks after the last stress episode. Immunohistochemistry was performed in rat's brains to evaluate perineuronal nets (PNNs) and parvalbumin GABA interneurons (PV) labeling as markers of inhibitory function in mPFC. ISD significantly decreased the preference for delayed large rewards in low impulsive, but not high impulsive, animals. ISD also increased the density of PNNs in the mPFC. These results suggest that increased choice impulsivity and cortical inhibition predispose animals to seek out rewards after stress.

Disease-causing Slack potassium channel mutations produce opposite effects on excitability of excitatory and inhibitory neurons

The KCNT1 gene encodes the sodium-activated potassium channel Slack (KCNT1, KNa1.1), a regulator of neuronal excitability. Gain-of-function mutations in humans cause cortical network hyperexcitability, seizures, and severe intellectual disability. Using a mouse model expressing the Slack-R455H mutation, we find that Na+-dependent K+ (KNa) and voltage-dependent sodium (NaV) currents are increased in both excitatory and inhibitory cortical neurons. These increased currents, however, enhance the firing of excitability neurons but suppress that of inhibitory neurons. We further show that the expression of NaV channel subunits, particularly that of NaV1.6, is upregulated and that the length of the axon initial segment and of axonal NaV immunostaining is increased in both neuron types. Our study on the coordinate regulation of KNa currents and the expression of NaV channels may provide an avenue for understanding and treating epilepsies and other neurological disorders.