Parvalbumin neurons in inferior colliculus mediate maladaptive inhibitory compensation in age-related hearing loss.

Tumor necrosis factor-alpha (TNF-α), a pleiotropic cytokine, modulates neuronal functions under both physiological and pathological conditions. In the auditory system, it is required for refinement of the cortical frequency map during early development. In adulthood, TNF-α upregulation following noise trauma contributes to synaptic imbalance and central auditory processing deficits. The effects of TNF-α deficiency on adult auditory cortical circuits and function have not been examined. Here, we report that compared to wild-type (WT) control mice (an equal number of males and females per group), adult TNF-α knockout (KO) mice had reduced PV neuron density and PV expression levels. Pyramidal neurons in the auditory cortex of TNF-α KO mice had larger miniature excitatory postsynaptic current (mEPSC) amplitude and lower miniature inhibitory postsynaptic current (mIPSC) frequency, suggesting a shift in synaptic E/I balance. Cortical multiunit had increased spontaneous and evoked activity and broadened tuning bandwidth consistent with the increased synaptic E/I ratio. Importantly, unlike WT mice, TNF-α KO mice exhibited persistent critical period-like plasticity into adulthood. Following exposure to a single-frequency tone, the representation of the tone was enlarged in adult TNF-α KO mice, but not in WT mice. Together with existing literature, our results suggest that TNF-α has a bell-shaped influence on adult auditory cortical circuits, with both elevated and deficient TNF-α expression leading to PV neuron dysfunction, increased synaptic E/I ratio, and enhanced cortical frequency map plasticity.Significance Statement Tumor necrosis factor-α (TNF-α) is a pleiotropic cytokine that contributes to the regulation of synaptic excitation-inhibition (E/I) balance. Sensory restriction is associated with increased TNF-α expression and an elevated synaptic E/I ratio. Here, we show that TNF-α-deficient mice have reduced parvalbumin-positive (PV) inhibitory interneuron density, an increased E/I ratio, impaired sensory restriction-induced homeostatic plasticity, and persistent critical period-like plasticity in adulthood. Together, these findings suggest a nonlinear, bell-shaped relationship between TNF-α signaling and cortical circuit function, in which both excessive and deficient TNF-α levels are associated with impaired PV interneuron function and increased E/I ratio.

Aversive 22-kHz ultrasonic vocalization playback reveals differences in affective (dys)function following early life adversity in male and female juvenile rats.

Baicalein alleviates anxiety symptom in Parkinson's disease by targeting Sema3A-mediated parvalbumin interneuron dysfunction.

Detecting statistical regularities in sound and responding to violations of these patterns, termed deviance detection, is a core function of the auditory system. In the human brain, studies have shown that deviance responses are enhanced in regular compared with random auditory contexts, but the underlying neuronal circuit mechanisms remain unclear. Here, we examined how inhibitory neurons contribute to context-dependent deviance responses in the mouse auditory cortex (AC). Using two-photon calcium imaging in AC of awake head-fixed male and female mice, we recorded neuronal activity during presentation of spectrotemporally rich moving ripple sounds, with deviant ripples embedded in either regular or random ripple sequences. AC neurons exhibited stronger responses to deviant sounds in regular contexts compared with random ones. To identify circuit mechanisms, we selectively inactivated parvalbumin (PV), somatostatin (SST), or vasoactive intestinal polypeptide (VIP) inhibitory neurons during the deviant stimulus presentation. Inactivation of PV and SST neurons broadly increased deviance responses in both contexts. In contrast, VIP inactivation selectively reduced responses to deviant stimuli in the regular, but not random, context, decreasing the context-dependent deviance signal enhancement. At the population level, inactivating all three neuronal subtypes increased detectability of the deviant stimulus, but the effects were context-dependent only for VIP inactivation. These findings reveal the distinct role of VIP neurons in modulating deviance signals based on context regularity, identifying a specific inhibitory neuron type that is critical for context-sensitive auditory processing and predictive coding.

Single-cell proteomics has advanced rapidly, but direct proteome measurements from identified neurons in intact brain tissue remain difficult because most workflows require cell isolation and recent patch-based studies have emphasized whole-soma retrieval. Here we show that aspiration-based patch proteomics enables deep proteome profiling of identified single neurons directly in acute mouse brain slices. We combined fluorescence-guided patch-clamp microsampling, minimal-loss bottom-up proteomics, and high-sensitivity capillary electrophoresis-timsTOF mass spectrometry to analyze partial somal aspirates from dopaminergic, parvalbumin, and serotonergic neurons in situ . The workflow identified more than 1,000 proteins from single-neuron samples under optimized conditions while consuming only about 0.25% of the processed digest per analysis. These proteomes were sufficient to separate biological replicates by neuronal phenotype, distinguish neuronal subtypes on the basis of protein expression alone, and define a conserved somal proteome shared across neuronal classes. Our results establish that controlled aspiration of partial somal material can support proteome-driven phenotyping without whole-soma retrieval, cell dissociation, or loss of native tissue context. Aspiration patch proteomics therefore provides an accessible route for subtype-level proteome phenotyping in intact brain tissue.

Amygdala stress-responsive ensembles mediate distinct susceptibility to negative stress-induced remote depression in adolescent and adult mice.

Human cortical interneurons differ from their rodent counterparts in intrinsic membrane properties, yet the mechanisms regulating excitability across physiologically relevant membrane potentials remain poorly defined. Here, we investigated inwardly rectifying potassium (Kir) channel control of subthreshold excitability in parvalbumin-expressing (Pvalb) interneurons from human and mouse neocortex. Using whole-cell recordings, dynamic clamp, patch sequencing, immunofluorescence, and computational modeling, we show that membrane hyperpolarization induces a proportional decrease in input resistance mediated by Kir channels in both species, despite higher baseline input resistance in human neurons. Transcriptomic and anatomical analyses revealed somatic membrane expression of four major Kir channel subtypes with moderate interspecies differences. Kir activation suppresses intrinsic excitability through combined voltage-dependent and shunting inhibition, an effect occurring during inhibitory postsynaptic potentials evoked by neurogliaform cells. Together, these findings show that homologous Pvalb neurons in humans have evolved toward a conserved, archetypal excitability phenotype, despite substantial differences in baseline excitability between species.

Neuronal Growth Regulator 1 (NEGR1) is a cell adhesion molecule involved in hippocampal circuit development and function. Human genetic studies have identified NEGR1 variants as risk factors for a broad spectrum of neuropsychiatric disorders. These disorders often display sex-specific differences in prevalence, progression, and behavioral impairment, reflecting underlying maladaptive changes in neural circuitry. Findings from preclinical studies using Negr1−/− mice show several hippocampal-based behavioral and anatomical endophenotypes relevant to neuropsychiatric disorders. The hippocampus, a key region implicated in these disorders, exhibits sex-dependent anatomical features that may shape the functional impact of Negr1. However, the mechanisms driving these sex-specific characteristics have not yet been elucidated. Here, we uncover sex-specific molecular signatures and pathways associated with Negr1, using Negr1−/− mice, a genetically relevant animal model for neuropsychiatric risk. We performed label-free quantitative proteomic analysis using eight replicates of hippocampi dissected from male and female wild-type, and Negr1−/− mice. Differentially abundant proteins were subjected to functional annotation for Gene Ontology and Protein-Protein interaction using STRING analysis. NEGR1 cellular localization was examined by immunofluorescent in rat brain and human hippocampal sections. Differential expression analysis identified 232 proteins in males and 172 in females. STRING analysis revealed sex-specific regulation of proteins. In males, proteins linked to neurofilament organization, myelin integrity, and postsynaptic structure were downregulated, with parvalbumin (Pvalb, PV) around the central node. In contrast, proteins related to mitochondrial and stress-response pathways were upregulated. Female Negr1−/− hippocampus showed downregulation of proteins involved in translation and amide biosynthetic processes. Colocalization of NEGR1 with PV interneurons in the rat brain and the human hippocampus was observed. We demonstrate, for the first time, distinct sex differences in the hippocampal proteome and identify molecular networks in Negr1−/− mice. Co-localization of NEGR1 and PV in human brain tissue provides anatomical and translational validation of a proteomic target. These findings provide new insight, offering a valuable resource for understanding NEGR1-related sex-specific mechanisms in neuropsychiatric disorders. The hippocampus is a key brain structure for learning, memory, and emotional regulation, and its dysfunction is central to several neuropsychiatric disorders, including major depression, schizophrenia, autism spectrum disorders, anxiety, and cognitive decline that are associated with Negr1 gene variants. The prevalence, expression, and course of neuropsychiatric disorders vary substantially between males and females. Neuronal Growth Regulator 1 (Negr1) is a member of the IgLON family of cell adhesion molecules. Negr1 is involved in the formation of neuronal circuits during prenatal and postnatal development. Negr1 deletion (Negr1−/−) in mice causes several abnormalities in the hippocampus, which underlie behavioral changes like those observed in a neuropsychiatric disorder. To understand the protein expression profile, protein-interaction network, and signaling pathways underlying Negr1-associated neurobehavioral pathology, we performed unbiased proteome analysis of the hippocampus from male and female Negr1−/− mice, which has not been done previously. We identified distinct sex-specific, differentially abundant proteins and biological pathways that differ between male and female tissues. We found that NEGR1 is located together with a special type of calming brain cell, known as parvalbumin neurons in rat and human brain, suggesting that they may work closely together in the brain. These would provide important data to further investigate the underlying sex-specific neurobiology of behavioral impairments related to Negr1 pathology.

BACKGROUND: This study investigates audiogenic seizures in Fmr1 knockout (KO) mice compared with wild-type (WT) mice across different ages. The aim was to assess auditory thresholds and examine glutamic acid decarboxylase (GAD) expression in auditory pathways to clarify the mechanisms underlying seizure susceptibility in fragile X syndrome (FXS). METHODS: Fmr1 knockout (KO) and wild-type (WT) FVB mice of different ages were used. Audiogenic seizure susceptibility was evaluated using sound stimulation. Auditory brainstem response (ABR) testing was performed to assess auditory thresholds, and glutamic acid decarboxylase (GAD) expression in auditory-related brain regions was examined by immunohistochemistry. Statistical analyses were conducted to compare KO and WT groups. RESULTS: Genetic identification confirmed Fmr1 gene knockout in all KO mice, which exhibited significantly lower seizure thresholds than WT mice (P < .05). Upon sound stimulation, KO mice displayed fear, running, and seizures with opisthotonus. Auditory brainstem response thresholds were significantly higher in KO mice at 3-4 weeks of age (P < .01), with no significant differences observed at 6-10 weeks (P > .05). Immunohistochemical analysis revealed significantly higher GAD expression in the auditory cortex, cochlear nucleus, and superior olivary complex of KO mice across all age groups (P < .01). CONCLUSION: Fmr1 KO mice exhibit age-dependent audiogenic seizures associated with transiently elevated auditory thresholds and increased GAD expression. These alterations suggest an imbalance of excitatory–inhibitory signaling within auditory circuits. Importantly, the findings also support the view that seizures in FXS are not solely the result of auditory system pathology, but rather reflect broader cortical abnormalities, including impaired inhibitory interneuron function and cortical network hyperexcitability. Emphasizing cortical contributions provides a more comprehensive explanation for seizure pathogenesis in FXS and aligns with recent evidence of cortical parvalbumin neuron degeneration in Fmr1-deficient models.

A developmental switch in corticoclaustral signaling.

Synapses are the fundamental units of neural computation, yet quantifying their organization across circuit-level scales remains a critical bottleneck in neuroscience. While advances in fluorescent labeling and imaging can generate vast datasets, analysis is often the limiting factor. Several deep learning-based tools have been proposed to ameliorate these issues. However, existing applications primarily focus on dendritic spines and lack robust solutions for segmenting synaptic puncta in dense tissue preparations. To address this, we introduce SynAPSeg, which encompasses an open-source framework for deep learning-based analysis and, to the best of our knowledge, the first large-scale, publicly available instance segmentation dataset specifically curated for synaptic puncta. We use this dataset to train deep learning models that reach the performance of human experts across a unique benchmark dataset. SynAPSeg integrates these models into an interactive interface, with support for multi-dimensional data, enabling fully automated segmentation and quantification pipelines alongside an annotation module for refinement and validation. We demonstrate the framework’s scalability by performing the first comprehensive mapping of nearly 4 million excitatory postsynaptic PSD95 puncta within inhibitory interneurons across the dorsal hippocampus, revealing regional differences in synapse properties. Finally, we show SynAPSeg’s utility for 3D quantification by applying these models to study aging-associated synaptic changes in CA1 parvalbumin (PV)-positive inhibitory neurons. Through this approach, we uncover a reduction in PSD95 density along PV dendrites in the aged CA1, indicating reduced glutamatergic recruitment of PV neurons which could contribute to age-related cognitive decline. Collectively, these results demonstrate that SynAPSeg provides a scalable solution for comprehensively studying synaptic architecture in health and disease.

Fast-spiking, nonadaptive inhibitory neurons in the thalamic reticular nucleus (TRN) critically gate the reciprocal communication between the thalamus and the cortex. Parvalbumin (PV) neurons express high levels of PV, the sole role of which appears to be calcium buffering. The significance of the PV protein-and its related high calcium-buffering capacity-under pathological conditions, especially in various neuropsychiatric disorders, is underappreciated. Deficiency of SHANK3, an important neuronal protein containing ankyrin, SH3, and PDZ, three canonical domains for protein recognition, causes behavioral changes relevant to autism spectrum disorders (ASDs). Here we report TRN PV neurons of Shank3-/- (exon 4-22 deletion) mice of either sex exhibit pronounced increases in burst firing occurrence, decreased tonic firing frequency, and faster dendritic calcium transient decay. We pinpointed reduced PV expression as the culprit and used the added buffer approach to confirm the decrease in calcium-buffering capacity in mutant neurons. Conversely, supplementing Shank3-/- PV neurons with extra EGTA reverses the abnormal action potential (AP) firing. In addition, the PV neurons from HCN2-/- mice exhibit consistent changes in neuronal excitability, PV expression, and calcium signaling. Together with the study of dopaminergic (DA) neurons in the ventral tegmental area (VTA), these results uncover reduced PV expression, calcium-buffering capacity, and altered neuronal excitability in Shank3-/- and HCN2-/- mice. This pathway, downstream of Shank3 deficiency and HCN channelopathy, may form an important pathological basis not only for ASD but also other neuropsychiatric disorders.

Morphometric dissimilarity in association cortices linked to autism subtype with more severe symptoms.

ABSTRACTBackgroundAlcohol use disorder (AUD) is a chronically relapsing condition marked by a pathological shift in behaviour, where excessive motivational drive predominates over cognitive control. Brodmann area 6 (BA6) is a key cortical region that integrates cognitive control with motor output and striatal circuits. Cellular alterations in the BA6 can shift from flexible, goal‐directed planning to habitual, compulsive behaviours.MethodHere, we examined cellular changes in the human post‐mortem cortex from AUD cases (n = 9) and age‐matched controls (n = 10). The density of parvalbumin (PV) neurons and perineuronal nets (PNN) was analysed from immunofluorescent‐stained sections. The number of PV neurons, PNN‐positive cells, and PV neurons colocalised with PNN across cortical layers II–VI in BA6 regions was quantified.ResultsAcross layers II/VI, the density of PV neurons and PNN was similar in the control and AUD groups, indicative of no cellular loss in the BA6. Analysis of the colocalisation of PV neurons with PNN revealed no effect in layers II/III (p = 0.720). However, there was a significant increase in colocalisation of PV neurons with PNN in layers IV (p = 0.043) and V/VI (p = 0.025) in the AUD compared to the control group.ConclusionThis study reveals layer‐specific remodelling of PNN and PV networks in the human cortex in AUD cases, suggesting shifts in AUD behaviours are potentially attributed to PV neuronal activity regulated by PNN in specific cortical layers. Together, this study identifies AUD‐related neuropathology and provides insight into the mechanisms underlying persistent alcohol‐seeking behaviour.

Opioid use disorder remains a major health challenge worldwide. Neuronal activity in the ventral pallidum (VP) regulates opioid reward and relapse to opioid seeking but the underlying cellular mechanisms remain largely unknown. A sizable population of VP neurons previously linked to drug relapse expresses the calcium binding protein parvalbumin (VPPV). Across the brain parvalbumin neurons are often ensheathed by perineuronal nets (PNNs), specialized extracellular structures that regulate intrinsic activity and constrain synaptic plasticity onto these neurons. The VP contains high levels of PNNs but the role of these structures in the neurophysiology of VPPV neurons and in relapse to opioid seeking has not been studied. To investigate whether VP PNNs are altered by opioid exposure, male and female mice were trained to self-administer intravenous heroin. We found that heroin increased the density of PNNs in the VP, and that an intracranial microinfusion of the PNN-degrading enzyme, chondroitinase ABC, prevented cue-induced reinstatement of heroin seeking. VP PNN depletion also reduced the intrinsic excitability of VPPV neurons, potentiated inhibitory synaptic inputs onto these cells, and diminished Fos expression in VPPV neurons following reinstatement. The suppressive effect of VP PNN depletion on heroin seeking was rescued by chemogenetic activation of VPPV neurons and mimicked by chemogenetic VPPV neuron inhibition. Taken together, our results identify VPPV neurons and their associated PNNs as critical drivers of opioid seeking. Given the key role of PNNs in regulating neural plasticity and memory processes, targeting PNNs in the VP could provide a useful novel therapeutic avenue for treating persistent craving and relapse in opioid use disorder.

Perinatal exposure to the organophosphorus insecticide chlorpyrifos (CPF) is associated with an increased incidence of neurodevelopmental disorders, such as autism spectrum disorder. While these behavioral detriments have been modeled in rodents, the underlying functional alterations in the developing brain are largely unknown. Previous reports using a rat model have identified alterations to both inhibitory synaptic transmission and serotonergic (5-HT) receptor binding in the cortex following developmental CPF exposure. Here, we use a rat model of gestational CPF exposure to investigate whether this altered inhibitory activity is driven by increased spontaneous firing of inhibitory interneurons and altered 5-HT receptor expression. Using cell-attached ex vivo electrophysiology in young rats of both sexes, we identified a significant increase in the number of spontaneously firing neurons in the somatosensory cortex of CPF-exposed offspring. Analysis of action potential metrics identified a subset of these neurons as fast-spiking parvalbumin (PV) interneurons. Immunohistochemical labeling of c-Fos, a marker of neuronal activity, further revealed a pronounced increase in activity of neurons of the somatosensory cortex in both juvenile and adult rats that had been gestationally exposed to CPF. Finally, RNAscope in situ hybridization showed an increase in the expression of the inhibitory receptor 5-HT1B in PV neurons of male offspring. The preliminary data reported here suggest that gestational exposure to CPF may result in persistent hyperexcitation of the somatosensory cortex. These neurophysiological effects may contribute to the established behavioral outcomes resulting from gestational exposure to CPF and offer guidance for novel preventative interventions.

Sensory cortices are not silent in the absence of sensory inputs but generate spontaneous activity intrinsic to the cortical circuit referred to as default-mode activity. Here, we report that spontaneous activity of excitatory and inhibitory neuronal types in layer 2/3 of the adult primary visual cortex (V1) exhibits quite stable default-mode local network architectures, which undergo rapid and selective restructuring following bilateral enucleation (EN), a model of adult-onset blindness. Spontaneous activity of both pyramidal (Pyr) and parvalbumin (PV) neurons rapidly and persistently increased following EN, but the default-mode network architecture of only Pyr rapidly rearranged and stabilized. Vasoactive intestinal peptide (VIP) neuronal network also restructured rapidly after EN, but their spontaneous activity increase was delayed. Somatostatin (SOM) neuronal network was quite stable. Our results indicate that adult-onset blindness rapidly and selectively modifies the stable default-mode local network architectures of V1, independent of increases in spontaneous activity, reflecting rapid adaptation to vision loss.

Sex-specific aggressive and emotional behavior in myostatin-deficient mice: Ratio of acylated versus unacylated ghrelin is reduced, but not correlated with butyrylcholinesterase activity level, however parvalbumin expression is lost in the habenular complex.

APOE4 is a risk factor for several disease states associated with cognitive impairment, including Alzheimer's disease and cancer-chemotherapy induced cognitive impairment. Using mouse knock-in models of human APOE alleles, we examined the effects of APOE genotype and chemotherapy on the ex vivo electrophysiological characteristics of excitatory and inhibitory neurons in the entorhinal cortex (EC). We found that APOE4 is associated with a significantly higher excitatory/inhibitory ratio (0.33 ± 0.04) in the layer 2/3 pyramidal cells of the entorhinal cortex compared to APOE3 (0.19 ± 0.04). We crossed APOE mice to mice with parvalbumin (PV) interneurons tagged with tdTomato, allowing us to measure effects specifically on this inhibitory cell type. For EC pyramidal neurons, the chemotherapeutic agent doxorubicin caused increases in the amplitudes of both spontaneous excitatory and inhibitory post-synaptic currents, with significant responses (***p < 0.001; **p < 0.01 respectively) in APOE3 brains. For EC PV neurons, APOE4 genotype was associated with significantly lower firing rates at injections of high currents (**p < 0.01), but rates were unaffected by doxorubicin. Doxorubicin doubled the percentage of PV cells that showed inactivation block in APOE3 brains (25% to 52%) but had no effect on APOE4 brains (50% to 54%). This ex vivo study suggests that APOE4 impairs homeostatic synaptic transmission in pyramidal cells under control conditions and causes a lack of responsiveness to a stressor (doxorubicin treatment) in PV cells.