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

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

Conditioning and pseudoconditioning differently change intrinsic excitability of inhibitory interneurons in the neocortex.

Many studies indicate a broad role of various classes of GABAergic interneurons in the processes related to learning. However, little is known about how the learning process affects intrinsic excitability of specific classes of interneurons in the neocortex. To determine this, we employed a simple model of conditional learning in mice where vibrissae stimulation was used as a conditioned stimulus and a tail shock as an unconditioned one. In vitro whole-cell patch-clamp recordings showed an increase in intrinsic excitability of low-threshold spiking somatostatin-expressing interneurons (SST-INs) in layer 4 (L4) of the somatosensory (barrel) cortex after the conditioning paradigm. In contrast, pseudoconditioning reduced intrinsic excitability of SST-LTS, parvalbumin-expressing interneurons (PV-INs), and vasoactive intestinal polypeptide-expressing interneurons (VIP-INs) with accommodating pattern in L4 of the barrel cortex. In general, increased intrinsic excitability was accompanied by narrowing of action potentials (APs), whereas decreased intrinsic excitability coincided with AP broadening. Altogether, these results show that both conditioning and pseudoconditioning lead to plastic changes in intrinsic excitability of GABAergic interneurons in a cell-specific manner. In this way, changes in intrinsic excitability can be perceived as a common mechanism of learning-induced plasticity in the GABAergic system.

Delineating mechanisms underlying parvalbumin neuron impairment in different neurological and neurodegenerative disorders: the emerging role of mitochondrial dysfunction.

Given the current paucity of effective treatments in many neurological disorders, delineating pathophysiological mechanisms among the major psychiatric and neurodegenerative diseases may fuel the development of novel, potent treatments that target shared pathways. Recent evidence suggests that various pathological processes, including bioenergetic failure in mitochondria, can perturb the function of fast-spiking, parvalbumin-positive neurons (PV+). These inhibitory neurons critically influence local circuit regulation, the generation of neuronal network oscillations and complex brain functioning. Here, we survey PV+ cell vulnerability in the major neuropsychiatric, and neurodegenerative diseases and review associated cellular and molecular pathophysiological alterations purported to underlie disease aetiology.

A vagal reflex evoked by airway closure.

Airway integrity must be continuously maintained throughout life. Sensory neurons guard against airway obstruction and, on a moment-by-moment basis, enact vital reflexes to maintain respiratory function1,2. Decreased lung capacity is common and life-threatening across many respiratory diseases, and lung collapse can be acutely evoked by chest wall trauma, pneumothorax or airway compression. Here we characterize a neuronal reflex of the vagus nerve evoked by airway closure that leads to gasping. In vivo vagal ganglion imaging revealed dedicated sensory neurons that detect airway compression but not airway stretch. Vagal neurons expressing PVALB mediate airway closure responses and innervate clusters of lung epithelial cells called neuroepithelial bodies (NEBs). Stimulating NEBs or vagal PVALB neurons evoked gasping in the absence of airway threats, whereas ablating NEBs or vagal PVALB neurons eliminated gasping in response to airway closure. Single-cell RNA sequencing revealed that NEBs uniformly express the mechanoreceptor PIEZO2, and targeted knockout of Piezo2 in NEBs eliminated responses to airway closure. NEBs were dispensable for the Hering-Breuer inspiratory reflex, which indicated that discrete terminal structures detect airway closure and inflation. Similar to the involvement of Merkel cells in touch sensation3,4, NEBs are PIEZO2-expressing epithelial cells and, moreover, are crucial for an aspect of lung mechanosensation. These findings expand our understanding of neuronal diversity in the airways and reveal a dedicated vagal pathway that detects airway closure to help preserve respiratory function.

Parvalbumin neurons in the nucleus accumbens shell modulate seizure in temporal lobe epilepsy.

A growing number of clinical and animal studies suggest that the nucleus accumbens (NAc), especially the shell, is involved in the pathogenesis of temporal lobe epilepsy (TLE). However, the role of parvalbumin (PV) GABAergic neurons in the NAc shell involved in TLE is still unclear. In this study, we induced a spontaneous TLE model by intrahippocampal administration of kainic acid (KA), which generally induce acute seizures in first 2 h (acute phase) and then lead to spontaneous recurrent seizures after two months (chronic phase). We found that chemogenetic activation of NAc shell PV neurons could alleviate TLE seizures by reducing the number and period of focal seizures (FSs) and secondary generalized seizures (sGSs), while selective inhibition of PV exacerbated seizure activity. Ruby-virus mapping results identified that the hippocampus (ventral and dorsal) is one of the projection targets of NAc shell PV neurons. Chemogenetic activation of the NAc-Hip PV projection fibers can mitigate seizures while inhibition has no effect on seizure ictogenesis. In summary, our findings reveal that PV neurons in the NAc shell could modulate the seizures in TLE via a long-range NAc-Hip circuit. All of these results enriched the investigation between NAc and epilepsy, offering new targets for future epileptogenesis research and precision therapy.

Perineuronal nets as regulators of parvalbumin interneuron function: Factors implicated in their formation and degradation.

The brain extracellular matrix (ECM) has garnered increasing attention as a fundamental component of brain function in a predominantly "neuron-centric" paradigm. Particularly, the perineuronal nets (PNNs), a specialized net-like structure formed by ECM aggregates, play significant roles in brain development and physiology. PNNs enwrap synaptic junctions in various brain regions, precisely balancing new synaptic formation and long-term stabilization, and are highly dynamic entities that change in response to environmental stimuli, especially during the neurodevelopmental period. They are found mainly surrounding parvalbumin (PV)-expressing GABAergic interneurons, being proposed to promote PV interneuron maturation and protect them against oxidative stress and neurotoxic agents. This structural and functional proximity underscores the crucial role of PNNs in modulating PV interneuron function, which is critical for the excitatory/inhibitory balance and, consequently, higher-level behaviours. This review delves into the molecular underpinnings governing PNNs formation and degradation, elucidating their functional interactions with PV interneurons. In the broader physiological context and brain-related disorders, we also explore their intricate relationship with other molecules, such as reactive oxygen species and metalloproteinases, as well as glial cells. Additionally, we discuss potential therapeutic strategies for modulating PNNs in brain disorders.

Acetylcholine Engages Distinct Amygdala Microcircuits to Gate Internal Theta Rhythm.

Acetylcholine (ACh) is released from basal forebrain cholinergic neurons in response to salient stimuli and engages brain states supporting attention and memory. These high ACh states are associated with theta oscillations, which synchronize neuronal ensembles. Theta oscillations in the basolateral amygdala (BLA) in both humans and rodents have been shown to underlie emotional memory, yet their mechanism remains unclear. Here, using brain slice electrophysiology in male and female mice, we show large ACh stimuli evoke prolonged theta oscillations in BLA local field potentials that depend upon M3 muscarinic receptor activation of cholecystokinin (CCK) interneurons (INs) without the need for external glutamate signaling. Somatostatin (SOM) INs inhibit CCK INs and are themselves inhibited by ACh, providing a functional SOM→CCK IN circuit connection gating BLA theta. Parvalbumin (PV) INs, which can drive BLA oscillations in baseline states, are not involved in the generation of ACh-induced theta, highlighting that ACh induces a cellular switch in the control of BLA oscillatory activity and establishes an internally BLA-driven theta oscillation through CCK INs. Theta activity is more readily evoked in BLA over the cortex or hippocampus, suggesting preferential activation of the BLA during high ACh states. These data reveal a SOM→CCK IN circuit in the BLA that gates internal theta oscillations and suggest a mechanism by which salient stimuli acting through ACh switch the BLA into a network state enabling emotional memory.

Basolateral amygdala parvalbumin interneurons coordinate oscillations to drive reward behaviors.

The basolateral amygdala (BLA) mediates both fear and reward learning.1,2 Previous work has shown that parvalbumin (PV) interneurons in the BLA contribute to BLA oscillatory states integral to fear expression.3,4,5,6,7 However, despite it being critical to our understanding of reward behaviors, it is unknown whether BLA oscillatory states and PV interneurons similarly contribute to reward processing. Local field potentials in the BLA were collected as male and female mice consumed sucrose reward, where prominent changes in the beta band (15-30 Hz) emerged with reward experience. During consumption of one water bottle during a two-water-bottle choice test, rhythmic optogenetic stimulation of BLA PVs produced a robust bottle preference, showing that PVs can sufficiently drive reward seeking. Finally, to demonstrate that PV activity is necessary for reward value use, PVs were chemogenetically inhibited following outcome devaluation, rendering mice incapable of using updated reward representations to guide their behavior. Taken together, these experiments provide novel information about the physiological signatures of reward while highlighting BLA PV interneuron contributions to behaviors that are BLA dependent. This work builds upon established knowledge of PV involvement in fear expression and provides evidence that PV orchestration of unique BLA network states is involved in both learning types.

Fragile X cortex is characterized by decreased parvalbumin-expressing interneurons.

Fragile X syndrome is a genetic neurodevelopmental disorder caused by a mutation of the fragile X messenger ribonucleoprotein 1 (FMR1) gene in the X chromosome. Many fragile X syndrome cases present with autism spectrum disorder and fragile X syndrome cases account for up to 5% of all autism spectrum disorder cases. The cellular composition of the fragile X syndrome cortex is not well known. We evaluated alterations in the number of Calbindin, Calretinin, and Parvalbumin expressing interneurons across 5 different cortical areas, medial prefrontal cortex (BA46), primary somatosensory cortex (BA3), primary motor cortex (BA4), superior temporal cortex (BA22), and anterior cingulate cortex (BA24) of fragile X syndrome and neurotypical brains. Compared with neurotypical cases, fragile X syndrome brains displayed a significant reduction in the number of PV+ interneurons in all areas and of CR+ interneurons in BA22 and BA3. The number of CB+ interneurons did not differ. These findings are the first to demonstrate that fragile X syndrome brains are characterized by cortical wide PV+ interneuron deficits across multiple cortical areas. These add to the idea that deficits in PV+ interneurons could disrupt the cortical balance and promote clinical deficits in fragile X syndrome patients and help to develop novel therapies for neurodevelopmental disorders like fragile X syndrome and autism spectrum disorder.

Mirrored might: A vision for inhibition.

In this issue of Neuron, Znamenskiy et al.1 unveil functional connection specificity between PV+ inhibitory interneurons and excitatory pyramidal neurons in mouse visual cortex, providing a circuit mechanism for stable amplification of cortical subpopulations.

Distinct electrophysiological properties of long-range GABAergic and glutamatergic neurons from the lateral amygdala to the auditory cortex of the mouse.

Differentiating between auditory signals of various emotional significance plays a crucial role in an individual's ability to thrive and excel in social interactions and in survival. Multiple approaches, including anatomical studies, electrophysiological investigations, imaging techniques, optogenetics and chemogenetics, have confirmed that the auditory cortex (AC) impacts fear-related behaviours driven by auditory stimuli by conveying auditory information to the lateral amygdala (LA) through long-range excitatory glutamatergic and GABAergic connections. In addition, the LA provides glutamatergic projections to the AC which are important to fear memory expression and are modified by associative fear learning. Here we test the hypothesis that the LA also sends long-range direct inhibitory inputs to the cortex. To address this fundamental question, we used anatomical and electrophysiological approaches, allowing us to directly assess the nature of GABAergic inputs from the LA to the AC in the mouse. Our findings elucidate the existence of a long-range inhibitory pathway from the LA to the AC (LAC) via parvalbumin-expressing (LAC-Parv) and somatostatin-expressing (LAC-SOM) neurons. This research identifies distinct electrophysiological properties for genetically defined long-range GABAergic neurons involved in the communication between the LA and the cortex (LAC-Parv inhibitory projections → AC neurons; LAC-Som inhibitory projections → AC neurons) within the lateral amygdala cortical network. KEY POINTS: The mouse auditory cortex receives inputs from the lateral amygdala. Retrograde viral tracing techniques allowed us to identify two previously undescribed lateral amygdala to auditory cortex (LAC) GABAergic projecting neurons. Extensive electrophysiological, morphological and anatomical characterization of LAC neurons is provided here, demonstrating key differences in the three populations. This study paves the way for a better understanding of the growing complexity of the cortico-amygdala-cortico circuit.

Agmatine ameliorates valproic acid-induced depletion of parvalbumin-positive neuron.

Autism spectrum disorder (ASD) is a widespread neurodevelopmental disorder with unknown etiology. Dysfunction of several brain areas including the prefrontal cortex (PFC), hippocampus, and cerebellum is involved in cognitive and behavioral deficits associated with ASD. Several studies have reported a reduction in the number of parvalbumin-immunoreactive (PV+) neurons in brain areas of ASD patients and animal models such as a shank mutant mouse model and rodents receiving fetal valproic acid (VPA) administration. Developing therapeutic interventions that restore PV interneurons can be the future therapeutic approach to ASD. The present study examined the possible effect of agmatine (AG), an endogenous NMDA antagonist, on the number of PV+ neurons in a VPA animal model of autism. The therapeutic effects of AG in ameliorating ASD-like behaviors were previously reported in VPA rats. AG was gavaged at dosages of 0.001, 0.01, and 0.1 mg/kg from gestational day (GD) 6.5 to 18.5, and the number of PV interneurons was analyzed by immunohistochemistry in the 1-month-old rats. Prenatal VPA (GD 12.5) or AG led to a decrease of PV neurons in the PFC, Cornu ammonia (CA1), and molecular layers (MLs) of the cerebellum. However, exposure to AG restored the PV population induced by VPA. AG may modify underlying neuronal mechanisms resulting in the increased survival or restoration of the PV population.

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.

Spine plasticity of dentate gyrus parvalbumin-positive interneurons is regulated by experience.

Experience-driven alterations in neuronal activity are followed by structural-functional modifications allowing cells to adapt to these activity changes. Structural plasticity has been observed for cortical principal cells. However, how GABAergic interneurons respond to experience-dependent network activity changes is not well understood. We show that parvalbumin-expressing interneurons (PVIs) of the dentate gyrus (DG) possess dendritic spines, which undergo behaviorally induced structural dynamics. Glutamatergic inputs at PVI spines evoke signals with high spatial compartmentalization defined by neck length. Mice experiencing novel contexts form more PVI spines with elongated necks and exhibit enhanced network and PVI activity and cFOS expression. Enhanced green fluorescent protein reconstitution across synaptic partner-mediated synapse labeling shows that experience-driven PVI spine growth boosts targeting of PVI spines over shafts by glutamatergic synapses. Our findings propose a role for PVI spine dynamics in regulating PVI excitation by their inputs, which may allow PVIs to dynamically adjust their functional integration in the DG microcircuitry in relation to network computational demands.

Parvalbumin and Somatostatin: Biomarkers for Two Parallel Tectothalamic Pathways in the Auditory Midbrain.

The inferior colliculus (IC) represents a crucial relay station in the auditory pathway, located in the midbrain's tectum and primarily projecting to the thalamus. Despite the identification of distinct cell classes based on various biomarkers in the IC, their specific contributions to the organization of auditory tectothalamic pathways have remained poorly understood. In this study, we demonstrate that IC neurons expressing parvalbumin (ICPV+) or somatostatin (ICSOM+) represent two minimally overlapping cell classes throughout the three IC subdivisions in mice of both sexes. Strikingly, regardless of their location within the IC, these neurons predominantly project to the primary and secondary auditory thalamic nuclei, respectively. Cell class-specific input tracing suggested that ICPV+ neurons primarily receive auditory inputs, whereas ICSOM+ neurons receive significantly more inputs from the periaqueductal gray and the superior colliculus (SC), which are sensorimotor regions critically involved in innate behaviors. Furthermore, ICPV+ neurons exhibit significant heterogeneity in both intrinsic electrophysiological properties and presynaptic terminal size compared with ICSOM+ neurons. Notably, approximately one-quarter of ICPV+ neurons are inhibitory neurons, whereas all ICSOM+ neurons are excitatory neurons. Collectively, our findings suggest that parvalbumin and somatostatin expression in the IC can serve as biomarkers for two functionally distinct, parallel tectothalamic pathways. This discovery suggests an alternative way to define tectothalamic pathways and highlights the potential usefulness of Cre mice in understanding the multifaceted roles of the IC at the circuit level.

Intersectional strategy to study cortical inhibitory parvalbumin-expressing interneurons.

Parvalbumin-expressing (PV) interneurons are key neuronal elements to a global excitatory-inhibitory balance in normal cortical functioning. To better understand the circuit functions of PV interneurons, reliable animal models are needed. This study investigated the sensitivity and specificity of the most frequently used PV-Cre/tdTomato mouse line in this regard. The colocalization of the transgene (tdTomato) with the parvalbumin protein, with GAD1 (a conclusive inhibitory cell marker) and Vglut1 (a conclusive excitatory cell marker) as well as with a marker for perineuronal nets (WFA) was assessed and a substantial proportion of layer 5 PV neurons was found to be excitatory and not inhibitory in the PV-Cre/tdTomato mouse. The intersectional transgenic mouse line Vgat-Cre/PV-Flp/tdTomato provided a solution, since no colocalization of tdTomato with the Vglut1 probe was found there. In conclusion, the Vgat-Cre/PV-Flp/tdTomato mouse line seems to be a more reliable animal model for functional studies of GABAergic PV interneurons.

Effective Regulation of Auditory Processing by Parvalbumin Interneurons in the Tail of the Striatum.

Parvalbumin (PV) interneurons in the auditory cortex (AC) play a crucial role in shaping auditory processing, including receptive field formation, temporal precision enhancement, and gain regulation. PV interneurons are also the primary inhibitory neurons in the tail of the striatum (TS), which is one of the major descending brain regions in the auditory nervous system. However, the specific roles of TS-PV interneurons in auditory processing remain elusive. In this study, morphological and slice recording experiments in both male and female mice revealed that TS-PV interneurons, compared with AC-PV interneurons, were present in fewer numbers but exhibited longer projection distances, which enabled them to provide sufficient inhibitory inputs to spiny projection neurons (SPNs). Furthermore, TS-PV interneurons received dense auditory input from both the AC and medial geniculate body (MGB), particularly from the MGB, which rendered their auditory responses comparable to those of AC-PV interneurons. Optogenetic manipulation experiments demonstrated that TS-PV interneurons were capable of bidirectionally regulating the auditory responses of SPNs. Our findings suggest that PV interneurons can effectively modulate auditory processing in the TS and may play a critical role in auditory-related behaviors.

Modulation of learning safety signals by acute stress: paraventricular thalamus and prefrontal inhibition.

Distinguishing between cues predicting safety and danger is crucial for survival. Impaired learning of safety cues is a central characteristic of anxiety-related disorders. Despite recent advances in dissecting the neural circuitry underlying the formation and extinction of conditioned fear, the neuronal basis mediating safety learning remains elusive. Here, we showed that safety learning reduces the responses of paraventricular thalamus (PVT) neurons to safety cues, while activation of these neurons controls both the formation and expression of safety memory. Additionally, the PVT preferentially activates prefrontal cortex somatostatin interneurons (SOM-INs), which subsequently inhibit parvalbumin interneurons (PV-INs) to modulate safety memory. Importantly, we demonstrate that acute stress impairs the expression of safety learning, and this impairment can be mitigated when the PVT is inhibited, indicating PVT mediates the stress effect. Altogether, our findings provide insights into the mechanism by which acute stress modulates safety learning.

Wired together, change together: Spike timing modifies transmission in converging assemblies.

The precise timing of neuronal spikes may lead to changes in synaptic connectivity and is thought to be crucial for learning and memory. However, the effect of spike timing on neuronal connectivity in the intact brain remains unknown. Using closed-loop optogenetic stimulation in CA1 of freely moving mice, we generated unique spike patterns between presynaptic pyramidal cells (PYRs) and postsynaptic parvalbumin (PV)-immunoreactive cells. The stimulation led to spike transmission changes that occurred together across all presynaptic PYRs connected to the same postsynaptic PV cell. The precise timing of all presynaptic and postsynaptic cell spikes affected transmission changes. These findings reveal an unexpected plasticity mechanism, in which the spike timing of an entire cell assembly has a more substantial impact on effective connectivity than that of individual cell pairs.

Gamma oscillation plasticity is mediated via parvalbumin interneurons.

Understanding the plasticity of neuronal networks is an emerging field of (patho-) physiological research, yet the underlying cellular mechanisms remain poorly understood. Gamma oscillations (30 to 80 hertz), a biomarker of cognitive performance, require and potentiate glutamatergic transmission onto parvalbumin-positive interneurons (PVIs), suggesting an interface for cell-to-network plasticity. In ex vivo local field potential recordings, we demonstrate long-term potentiation of hippocampal gamma power. Gamma potentiation obeys established rules of PVI plasticity, requiring calcium-permeable AMPA receptors (CP-AMPARs) and metabotropic glutamate receptors (mGluRs). A microcircuit computational model of CA3 gamma oscillations predicts CP-AMPAR plasticity onto PVIs critically outperforms pyramidal cell plasticity in increasing gamma power and completely accounts for gamma potentiation. We reaffirm this ex vivo in three PVI-targeting animal models, demonstrating that gamma potentiation requires PVI-specific signaling via a Gq/PKC pathway comprising mGluR5 and a Gi-sensitive, PKA-dependent pathway. Gamma activity-dependent, metabotropically mediated CP-AMPAR plasticity on PVIs may serve as a guiding principle in understanding network plasticity in health and disease.