Frontiers in Molecular Neuroscience

Lysosomal trafficking and homeostasis are biological functions that are pivotal for DRG neurons, given their metabolic demands and extremely long axons. Previous studies indicate that lysosomal signaling is altered in a mouse model of chemotherapy-induced peripheral neuropathy (CIPN) and that blocking mitogen activated protein kinase-associated kinase (MNK1/2) signaling can alleviate pain behaviors in CIPN. Here, we investigated lysosome dynamics and lysosome-associated signaling in a mouse model of CIPN induced by paclitaxel (PTX), a chemotherapeutic agent used for various types of cancer. Using spinning disk super-resolution microscope (SPINSR), we demonstrate that PTX treatment in vivo causes reduced lysosome motility observed in vitro. PTX likewise drives the accumulation of Sequestosome 1 (SQSTM1), also known as P62, in cultured mouse DRG neurons, indicating lysosomal dysfunction in DRG neurons. The transcription factor EB (TFEB), a master regulator of lysosomal biogenesis, was also upregulated in the nucleus of cultured mouse DRG neurons treated with PTX. In line with this, increased lysosomal-associated membrane protein 1 (LAMP1) expression was observed in PTX-treated mice. Given that our previous work demonstrated PTX treatment increases MNK1/2-eIF4E signaling in DRG neurons, we examined whether MNK1/2 inhibition could rescue lysosomal dysfunction. Treatment with Tomivosertib (eFT508), a potent MNK1/2 inhibitor, restored P62 levels in DRG neurons of PTX-treated mice and reduced TFEB in DRG treated in vitro. To establish translation relevance, we further show that PTX elevates phosphorylated eiF4E (p-eIF4E) in human DRG neurons, and concurrent eFT508 administration attenuates this effect. Collectively, these findings indicated that PTX disrupts lysosome trafficking and biogenesis, and that MNK inhibition with eFT508 restores lysosomal signaling and can serve as a neuroprotective strategy for CIPN.

Phagocytic and immune-like cells have been observed in the satellite envelope of neuronal somata in peripheral sensory ganglia of many species for several decades. These cells likely play an important role in normal function of sensory neurons and they may also play an important role in neuronal dysfunction and neurodegeneration seen with neuropathy. Recent findings have described a satellite macrophage population transcriptomically similar to microglia in peripheral ganglia of some mammalian species. The function of these cells, and the mechanisms by which they may influence neurons in neuropathy are unclear. We sought to understand the phenotype and localization of these cells in the human dorsal root ganglion (hDRG) using large-scale single nucleus and spatial transcriptomic datasets from individuals with and without a history of peripheral diabetic neuropathy. We observed a large population of macrophages that express classical microglia makers such as TMEM119 and P2RY12 in the hDRG, as previously described. Our findings confirm that these microglia-like cells (MLCs) localize to the satellite envelope around neuronal somata, yet are transcriptomically distinct from all glial cell types characterized in the hDRG. These MLCs exhibit changes in abundance and localization with diabetic painful neuropathy (DPN) in both the hDRG and sural nerves suggesting that they are not exclusively localized to the DRG. We conclude that microglia-like cells are likely the resident tissue macrophage (RTM) of the hDRG, and perhaps the peripheral nervous system (PNS) given their localization to the sural nerve and other ganglia, where they are predicted to regulate homeostatic neuronal functions and response to injury. HighlightsO_LIMLCs are likely the RTM of hDRGs C_LIO_LIMLCs localize to the satellite envelope and recede with Nageotte nodule formation C_LIO_LIMLC activation state and signaling shift with diabetic neuropathy C_LIO_LIMLCs are also present in other ganglia and sural nerve C_LI

The hippocampal formation (HPF) provides neural substrates integrating disparate sensory cues into episodic memories and coherent action. Whereas HPF structures are formed by birth, the functional circuits evolve over postnatal development. Our previous studies showed that transient perinatal expression of the serotonin (5-HT) transporter SERT/Slc6a4 in CA3 pyramidal neurons, which do not synthesize 5-HT but take up extracellular 5-HT thus termed "5-HT-absorbing neurons", exerts sex-biased effects on long-term activity-dependent HPF synaptic plasticity and behavior in mice. This study investigates SERT impact on circuit development, through single-nucleus transcriptomics of postnatal HPF from CA3-pyramidal neuron SERT knockout (SERTPyramid{Delta}) mice. We demonstrate that SERTPyramid{Delta} mice preserve cell identities across the HPF but alter gene expression in specific neuronal types in a sex-biased manner. We observed SERTPyramid{Delta} male-biased upregulation of genes preferentially in glutamatergic neurons, particularly affecting the CA2 and parasubiculum (PaS) when they develop social novelty and spatial representations, respectively. In both the CA2 and PaS, altered genes center on two categories -- modulators of gene expression patterning including chromatin plasticity, RNA processing and ubiquitin-dependent protein degradation, and aspects of synaptic transmission. >20% of the dysregulated genes in the CA2 and PaS are associated with Autism and engaged in cell-type distinct functional networks, showing CA3 SERT regulation of ASD-vulnerable genes in intersecting biological processes in specific neurons during social and spatial circuits development. The data, available at https://scviewer.shinyapps.io/hippocampus_sertKO, provide an entry map for further deducing anatomical neuronal origin and the molecular and cellular pathways impaired by 5-HT dysfunction during HPF circuits development leading to lifetime cognitive deficits.

Organotypic slice cultures (OSCs) are widely used to study cellular properties in a functional and developmental tissue context. With the recent advent of transgenic mouse lines and viral tools we postulated that OSCs may enable the study of multicellular glial and neuroglial interactions in development, as well homeostatic and pathological conditions. Here, we made mouse cortical OSCs and used markers for oligodendroglial, microglial states and neuronal types between 1 to 28 days in vitro (DIV). The OSC was characterized by in-vivo like cortical layering, including layer 5 pyramidal neurons and produced highly robust synchronized period bursts resembling Up- and Down states. Glial cells showed a strong cortical layer- and time-dependent development pattern: in the first week (DIV 1-7), slicing-related debris clearance and developmentally restricted sparse oligodendroglial myelination created an environment with highly phagocytic, non-homeostatic microglia (assessed with CD68 and purinergic receptor P2Y12, respectively). Between DIV 14 and 21, however, slices showed stereotypical cortical myelin patterns and the emergence of a homeostatic microglia phenotype while exhibiting continued phagocytosis. Furthermore, live two-photon imaging and morphometric analyses revealed highly ramified microglia and myelinated axons with compact myelination, exceeding lamellae count compared to age-matched in vivo axons. Lastly, from DIV 28 and onwards, myelin integrity became impaired and associated with phagocytic microglia. Together, the results indicate that between DIV14 and 21 cortical OSCs are well suited for live imaging of homeostatic and activity-dependent neuron-glia interactions, bridging the gap between in vivo investigations and primary cell cultures.

Electrical transmission is mediated by intercellular channels that cluster into structures known as gap junctions (GJ). In vertebrates, GJ channels are encoded by the gene family of connexin (Cx) proteins that assemble as hexamers, termed hemichannels, in the pre- and postsynaptic membranes, and that subsequently dock to form GJ channels. Auditory contacts on the fish Mauthner cells serve as model to study the properties and organization of vertebrate electrical synapses. Electrical transmission at these synapses is mediated by multiple co-existing GJs at which the presence of intercellular channels is regulated by a molecular scaffold. Zebrafish contain four homologs of the neuronal Cx36: Cx35.5 and Cx35.1 (gjd2a and b, respectively), and Cx34.1 and Cx34.7 (gjd1a and b). Cx mutations suggested that GJs are formed by heterotypic channels made of presynaptic Cx35.5 and postsynaptic Cx34.1. Using transgenic fish in which Cxs were tagged, we found that a second Cx, Cx34.7, is present together with Cx34.1 on the postsynaptic side at some but not all GJs at these terminals. When exogenously expressed, both Cx34.1 and Cx34.7 formed heterotypic functional channels with Cx35.5, each with substantially different voltage-dependent properties, indicating they can serve differential functions. However, we previously demonstrated that electrical transmission is lost in Cx34.1 but not Cx34.7 null mutants, suggesting that Cx34.7 cannot compensate for the loss of Cx34, despite the intrinsic ability of Cx34.1 and Cx34.7 to create functional channels. The findings reveal an unanticipated functional organization in the electrical synapse, where Cx34.1 is obligatory and Cx34.7 accessory, roles that appear to be defined by the postsynaptic molecular scaffold, with two postsynaptic Cxs possibly assembling under specific functional contexts. Thus, our results indicate that electrical synapses share an organizational motif with chemical synapses, akin to how they combine postsynaptic receptor types to modify synaptic function.

Among mammals, spiny mice (Acomys spp.) exhibit the unique capacity to regenerate parts of their nervous system. Studying this phenomenon has the potential to reveal new targets that can slow or halt human neurodegenerative disorders. Unfortunately, research tools (e.g., transgenic lines, gene delivery vehicles) are lacking compared to those available for other rodent models. Here, we tested systemic adeno-associated viral vectors (AAVs) in Acomys dimidiatus and identified three promising candidates: X1.1, CAP-Mac, and MaCPNS1. Characterizing their tropism following intravenous delivery, we found that in the brain, MaCPNS1 and X1.1 primarily transduced astrocytes. In the peripheral nervous system, MaCPNS1 efficiently transduced dorsal root ganglia, axon bundles of the ear pinnae, and enteric neurons throughout the gastrointestinal tract. As a proof-of-concept, we used MaCPNS1 to chemogenetically modulate the activity of enteric neurons, successfully decreasing gastric motility in vivo and increasing colonic motility ex vivo. We expect these findings to enable functional studies of the uniquely regenerative nervous system of Acomys, which may in turn help advance neuroregenerative therapeutics for humans. Summary StatementIdentification of an AAV tool to efficiently deliver transgenes to the central and peripheral nervous systems of spiny mice enables functional studies of the nervous system in a mammalian model of regeneration.

The peripheral auditory system of dolphins comprises specialised bony, fatty, vascular, and neural structures adapted for underwater hearing and diving physiology. These include the external ear canal, acoustic fat bodies, sinuses, and associated neurovascular networks, which together support sound conduction, protection, and possibly sensory functions. Despite advances in gross anatomical description, the detailed integration of these tissues, particularly the innervation, neurovascular organisation, and their functional implications, remains poorly understood. Previous studies have described the presence of sensory nerve formations and vascular plexuses, but their arrangement, connectivity, and relation to each other are unresolved. Here, we combine macroscopic dissection, DICE-{micro}CT, histology, and high-resolution confocal microscopy to characterise several neurovascular and sensory components of the dolphin peripheral auditory system in several delphinid species. Macroscopic dissection and DICE-{micro}CT revealed the traditional acoustic fat body distribution with detailed morphology of the posterolateral extension that is not well-known. The cranial nerve distribution, and specifically the mandibular nerve branching patterns, are described in detail. Confocal microscopy uncovered a stratified neurovascular plexus around the external ear canal with a complex sensory system comprising lamellar corpuscles, Merkel cell-neurite complexes, and intraepithelial nerve fibres. Notably, the lamellar corpuscles formed a continuous, three-dimensional neural network with frequent merging and splitting of axonal bundles, shared perineuria, and vascular integration, features not observed in previous studies. Our findings demonstrate that the dolphin external ear canal and surrounding structures form a sophisticated, multimodal somatosensory organ, integrating structural, vascular, and neural specialisations likely adapted for proprioceptive mechanosensation in the aquatic environment. This study provides insights into the integration of the various components of the peripheral hearing apparatus. Future studies integrating anatomical, electrophysiological, and biomechanical approaches are needed to fully elucidate these adaptations.

Estrogen-related receptor gamma (ESRRG), an orphan nuclear receptor with structural homology to the classical estrogen receptors, is widely recognised as a key metabolic regulator involved in mitochondrial, synaptic, and ion-homeostatic pathways. Previous clinical studies suggest a link between ESRRG and auditory function; for example, ESRRG has been associated with susceptibility to age-related hearing loss in women and implicated in congenital hearing loss. However, the biological mechanisms by which ESRRG may mediate hearing function remain largely unknown. Here, using a combination of in vivo auditory physiological recordings, immunofluorescence analyses, single hair-cell electrophysiology, and transcriptomic approaches, we characterise the phenotype of a new inner-ear conditional Esrrg knockout (Esrrg-cKO) to investigate the role of Esrrg in the auditory system. We found that Esrrg-cKO mice of both sexes develop early-onset hearing loss, as evidenced by elevated auditory brainstem response thresholds and reduced wave 1 amplitudes from two weeks of age. These auditory deficits arise from a combination of early-onset cochlear neuronal and innervation malformations, together with inner hair cell synaptic defects and delayed myelination that persist into adulthood. Furthermore, distortion product otoacoustic emissions and endocochlear potential recordings are normal in Esrrg-cKO mice, and although sensory hair cells are preserved, IHCs retain immature biophysical properties. These findings are consistent with auditory neuropathy, and together with our comparative transcriptome analyses, indicate that Esrrg is an essential molecular driver of normal cochlear innervation and maturation.

The past decade has seen tremendous progress in the identification of genes associated with complex neuropsychiatric disorders, including autism spectrum disorder (ASD) and schizophrenia. Expression patterns of these genes in single cell data strongly implicate excitatory and inhibitory neurons; however, there are limited data on the brain regions involved - a critical question for neurobiology. Spatial transcriptomics provide an opportunity to perform systematic multiregional analyses to provide insights into this question. Here, we have generated a spatial transcriptomics dataset encompassing the diverse anatomical territories of the adult mouse brain sagittal midsection. We compare neuropsychiatric gene enrichment by applying Gene Fraction Enrichment Score (GFES), a novel statistic method that controls for differing neuronal proportions across regions. ASD-associated genes identified by exome sequencing were most enriched in the thalamus followed by the cortex. Schizophrenia genes from genome-wide association studies were also enriched in the thalamus, along with the hippocampus and cortex. These findings add to the evidence that the thalamus plays a major role in neuropsychiatric disorders whilst supporting roles for the cortex and hippocampus. The results highlight shared and distinct patterns for pleiotropic brain disorders that could elucidate common underlying mechanisms and circuitry.

Atopic dermatitis (AD) is a highly prevalent, relapse-remitting, inflammatory skin disease, the hallmark symptom of which is chronic itch. Mechanisms underlying AD itch are multifactorial, involving various cells, receptors, and mediators. Developing a physiologically relevant, human model system for AD itch research and drug development is crucial. To this end, human induced pluripotent stem cell-derived sensory neurons (iPSCSNs) were cultured with human primary keratinocytes to form deconstructed skin models. Using Ca2+-imaging in a direct contact, 2.5D co-culturing format, which mimics natural skin innervation and permits both paracrine exchange and juxtacrine signaling, iPSCSNs exhibited functional TRPA1 responses not seen in monotypic iPSCSN cultures or in iPSCSNs conditioned with keratinocyte medium. Different AD-associated cytokines were used to stimulate the co-culture systems to mimic an inflamed lesional skin environment, whereby TNF was found to increase iPSCSN chemosensitivity. Finally, both TRPA1 and JAK1/2 inhibition reduced iPSCSN responses to pruritogens (TSLP, IL-31), thus supporting TRPA1 as a therapeutic target for AD itch in humans. This study demonstrates that human deconstructed skin models can be a useful tool in AD and broader pruritus research. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=181 SRC="FIGDIR/small/724000v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@11c0c9borg.highwire.dtl.DTLVardef@7fa518org.highwire.dtl.DTLVardef@2fe7a2org.highwire.dtl.DTLVardef@1105fa7_HPS_FORMAT_FIGEXP M_FIG C_FIG

Octopamine is involved in a variety of different physiological and behavioral mecha-nisms in Drosophila melanogaster. Throughout the life cycle of the fruit fly, from the larva to the adult, octopaminergic neurons in both the central and the peripheral nerv-ous system target a multitude of neurons and even non-neuronal tissues, making it challenging to analyze individual mechanisms of octopamine function. One approach to deconstructing this complex system is to examine the postsynaptic components of signal transmission. In Drosophila, octopamine interacts with six distinct G-protein-coupled receptors. For some of these receptors, expression maps and functional im-plications have been described. In contrast, other receptors have been neglected, partly due to the lack of suitable genetic tools. Here, for the first time, we compiled a complete set of mutant lines of all known octopamine receptors, all generated using the same genetic tool, the recently established Trojan Exon system. It integrates the Gal4/UAS binary expression strategy while simultaneously impairing receptor func-tion. This enabled us to generate a comprehensive anatomical map of receptor ex-pression in the larva and, at the same time, analyze the function of individual octopa-mine receptors during larval development, chemosensory perception and locomotion. All octopamine receptors (Oamb, Oct2R, Oct{beta}1R, Oct{beta}2R, Oct{beta}3R, and Oct-TyrR) showed extensive signal in the central nervous system. The same was found for the peripheral nervous system, with the exception of Oct{beta}2R, which showed pronounced expression in the somatic muscles. We also observed a previously undescribed role of Oct{beta}1R, Oct{beta}3R, and Oct-TyrR in larval hatching and in the survival of larvae and pupae. Molecular evaluation of the Trojan Exon octopamine lines supports our analy-sis. In addition, we combined the experimental results with gene expression data from the different development stages of Drosophila melanogaster and from different tis-sues and cell populations throughout the body. Overall, we compiled, analyzed and validated a complete set of octopamine lines which, together with gene expression analysis, provides a basis for further functional studies on the larval octopaminergic system.

Friedreichs ataxia (FA) is a rare autosomal recessive neurodegenerative disorder caused by reduced expression of frataxin, a mitochondrial protein important for iron-sulfur cluster assembly and mitochondrial homeostasis. Although FA has traditionally been attributed to neuronal dysfunction, increasing evidence suggests that glial cells play a critical role in disease progression, although their contribution remains poorly defined. Using the FXNI151F mouse model, we investigated cell-type-specific metabolic and redox alterations in neurons and glial populations from the cerebrum, cerebellum, and dorsal root ganglia (DRG). Neuronal and glial-enriched fractions were isolated by immunomagnetic separation and analyzed for mitochondrial function, iron metabolism and reactive oxygen species (ROS). The analyses identified the DRG as the most severely affected region, exhibiting early and pronounced mitochondrial respiratory deficits, increased ROS, mitochondrial iron accumulation, lipid peroxidation, and reduced levels of glutathione peroxidase 4 and nuclear factor erythroid 2-related factor 2 in both neuronal and non-neuronal cells. These results highlight the vulnerability of sensory neurons and their supporting satellite glial cells. In contrast, in the cerebrum and cerebellum, astrocytes displayed earlier and more severe alterations than neurons, including impaired respiratory chain efficiency, disrupted complex I-III supercomplex interaction, elevated ROS, and hallmarks of ferroptosis. Neuronal abnormalities emerged later, suggesting that glial dysfunction precedes -or drives- neuronal pathology within the central nervous system. Overall, these findings reveal pronounced region and cell-type-specific vulnerabilities in FA and support the importance of targeting glial mechanisms--particularly iron dysregulation, oxidative stress, and ferroptosis-- as targets for potential therapeutic strategies.

Local protein synthesis in neurons occurs in both axons and dendrites and plays a central role in synaptic function. High-throughput-based sequencing and imaging studies have demonstrated the presence and translation of synaptically localised mRNAs. However, quantification of activity-dependent translation dynamics at synapses at the transcriptome-wide scale remains limited. Here, we apply ribosome profiling to synapse-enriched fractions (synaptoneurosomes) derived from rat cortical tissue following stimulation with the group 1 mGluR agonist DHPG. DHPG stimulation induced translation of mRNAs involved in synaptic processes, including synaptic vesicle exocytosis and axo-dendritic transport. Notably, translation of ribosomal protein mRNAs was upregulated upon mGluR activation, consistent with the expected increase in de novo protein synthesis. Together, these results demonstrate the use of ribosome profiling to capture changes in local mRNA translation from isolated preparations.

CaMKII promoter is widely used to label and manipulate hippocampal pyramidal neurons via transgenic mouse lines or viral approaches. While it targets most excitatory neurons, a small subset remains unlabeled and often overlooked. We present an AAV-based strategy combined with CaMKII-driven Cre expression to access and study this remaining population. Furthermore, we provide a detailed protocol for in-house AAV production, targeted stereotaxic delivery, and functional validation of targeted neurons through slice electrophysiology and behavior. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=194 HEIGHT=200 SRC="FIGDIR/small/723440v1_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@3a31ccorg.highwire.dtl.DTLVardef@9b7e90org.highwire.dtl.DTLVardef@92297borg.highwire.dtl.DTLVardef@1e159eb_HPS_FORMAT_FIGEXP M_FIG C_FIG

Oligodendrocyte-enriched cortical organoids (OCOs) are a powerful platform for modeling oligodendrogenesis in a human cellular context. However, neuronal activity is impaired in conventional culture media, limiting assessment of neuronal function in conjunction with oligodendrocyte biology. To address this, we used a modified BrainPhys medium termed neuronal activity medium (NAM) and defined the optimal developmental window for NAM exposure to generate OCOs with robust neuronal activity (NAM-OCOs). Stage-specific exposure to NAM, prior to oligodendrocyte expansion, leads to enhanced structural maturation, as evidenced by increased organoid size, heightened synaptogenesis, and upregulation of transcripts associated with neuronal complexity. Further, NAM-OCOs display increased cellular heterogeneity, including greater representation of GABAergic interneurons while preserving oligodendrocyte development and maturation. Altogether, our studies demonstrate that stage-specific exposure to an activity-permissive environment enhances neuronal activity, establishing an OCO model which integrates neuronal activity with oligodendrocyte development and maturation. HighlightsO_LIIncreased neuronal activity in oligodendrocyte-enriched cortical organoids (OCOs) C_LIO_LIStage-specific Neuronal Activity Medium (NAM) optimizes activity C_LIO_LINAM-OCOs display increased cellular heterogeneity and neuronal maturation C_LIO_LIOligodendrogenesis is preserved in NAM-OCOs C_LI eTOC blurbIn this article, Chung et al enhance neuronal activity in oligodendrocyte-enriched cortical organoids (OCOs) through stage-specific exposure to Neuronal Activity Medium (NAM). OCOs exposed to NAM display elevated cellular heterogeneity, structural maturation, and synaptogenesis, while preserving oligodendrocyte development and maturation. These results establish an increasingly comprehensive OCO model for studying neuronal function and oligodendrogenesis.

Tourette syndrome (TS) is a neurodevelopmental disorder of childhood onset characterised by vocal and motor tics and is associated with cortical-striatal-thalamic-cortical circuit [CSTC] dysfunction. TS often follows a developmental time course in which tics become increasingly more controlled during adolescence. However, many individuals continue to have debilitating tics into adulthood. This indicates that there may be important differences between adults with TS for whom the clinical phenotype is more stable, and children and adolescents with the disorder who may be undergoing developmental neuroplastic changes linked to the reduction of their tics. Previous studies have used transcranial magnetic stimulation (TMS) to investigate changes in cortical motor excitability in individuals with TS, including measurement of resting motor threshold (RMT). However, the findings from these studies have been mixed, have varied between adult and child samples, and have often been based on small sample sizes. Here we report a multi-centre, mega-analytic, study in which RMT data collected from children and adults with TS at multiple research centres was pooled for analysis. Results confirmed that mean RMT was significantly increased in individuals with TS compared to neurotypical controls. However, this result can be explained by the more important findings that: (a) RMT for adults with TS did not differ from that of neurotypical adults; and (b) the rate that RMT decreases with age during childhood and adolescence is reduced in individuals with TS compared to controls. Thus, while neurotypical individuals reach an adult RMT level by ~12-13 years of age, individuals with TS are substantially delayed in doing so, and do not reach an adult RMT level until much later, at ~24 years of age. We conclude therefore that differences in measures of cortical excitability between children and adolescents with TS and chronologically age-matched neurotypical controls may likely reflect a developmental delay in the maturation of functional brain networks in individuals with TS, which may normalise with age.

Vestibular neurons are core elements of the pathways involved in vestibulo-motor functions, such as vestibulo-spinal and vestibulo-ocular reflexes. To meet behavioral needs, electrophysiological neuronal properties are adequately adapted to the sensory-motor computation sustaining these distinct vestibular reflexes. During frog metamorphosis, there is a complete reorganization of the posturo-locomotor system while the oculomotor system remains minimally changed, probably associated to so far unknown changes in vestibular neuronal properties. We used this unique model to investigate the central developmental mechanisms underlying such a reconfiguration of vestibular-associated behaviors. Central vestibular neurons exhibit two types of electrophysiological phenotypes: tonic neurons with a continuous discharge and phasic neurons with a transitory discharge mainly due to the activation of Kv1.1 channel. Electrophysiological recordings and Kv1.1 immunolabeling of vestibulospinal (VS) and vestibulo-ocular (VO) neurons at both larval and juvenile stages revealed that the majority of VS neurons exhibited a tonic discharge in larvae but a phasic discharge in juvenile, while VO neurons remained mainly tonic throughout development. Changes in phasic and tonic neurons proportions in VS population are partly explained by neurogenesis. But we provide evidences that an electrophysiological phenotype switch is a concomitant developmental mechanism participating in the maturation of these central vestibular neurons. All together our results showed that the maturation process in central vestibular neuronal groups is highly related to the metamorphosis-induced remodeling of vestibulo-motor functions they are involved in, with the ultimate purpose of ensuring an adequate adaptation of neuronal elements properties to the developmental changes of behavioral constrains.

Aging and noise over-exposure lead to complex mixtures of cochlear degradation that impair the structure and function of outer hair cells, inner hair cells (IHCs), and the cochlear nerve. However, IHC damage and cochlear synaptopathy (CS) remain pathologies "hidden" from the audiogram. This study aimed to identify and differentiate the physiological signatures of these two distinct pathologies using promising non-invasive assays: Envelope Following Responses (EFRs), Auditory Brainstem Response (ABRs), Wideband middle-ear reflexes (WB-MEMRs), and Distortion Product Otoacoustic Emissions (DPOAEs). We utilized chinchilla models of carboplatin-induced (CA) IHC damage (N = 4) and temporary threshold shift (TTS) noise-induced CS (N = 4) to compare the physiological signatures of each pathology. While both groups showed unchanged ABR thresholds two weeks after exposure, EFRs, ABR Wave V/I ratios, and MEMRs showed distinct effects of exposure. Despite non-elevated ABR-derived audiometric thresholds after exposure, both CA and TTS exposure resulted in severe in EFR "peakiness", particularly for sharp, short-duty-cycle stimuli and significant elevations in ABR Wave V/I ratios. However, these findings were less-pronounced in the TTS-exposed animals. WB-MEMR amplitudes were decreased with elevated thresholds in both groups; this effect was more pronounced in the TTS group. Opposite trends in DPOAE amplitudes indicated that while both IHC damage and CS result in similar suprathreshold temporal coding deficits, effects on outer-hair-cell integrity and auditory efferent physiology may differ between the two pathologies. Future work and novel diagnostics should aim to distinguish these specific cochlear pathologies in clinical populations, or at the very least consider their overlap. HighlightsO_LIA multi-metric diagnostic approach was used with chinchilla models of inner-hair-cell (IHC) damage and cochlear synaptopathy (CS). C_LIO_LIIHC damage and synaptopathy both cause suprathreshold deficits "hidden" from the audiogram. C_LIO_LIIHC damage results in more severe temporal envelope coding degradation than does synaptopathy. C_LIO_LIA combination of EFR "peakiness", ABR Wave V/I ratio, and Wideband Middle Ear Muscle Reflex (WB-MEMR) appear to be useful measures for profiling IHC damage and CS. C_LI

Neuropilin-1 (NRP1) is a single pass transmembrane glycoprotein that can form a receptor complex with several tyrosine kinase receptors, including the vascular endothelial growth factor (VEGF) receptor. Previous studies have reported that binding of VEGFA to this receptor complex elicits mechanical allodynia and thermal hyperalgesia through potentiation of voltage-gated sodium and calcium channel activity. We find that Nrp1 mRNA and protein is widely distributed in naIve mouse and rat DRG neurons, including peptidergic afferents. A CGRPcreER: NRP1fl/fl transgenic mice was generated to investigate the role of peptidergic NRP1 in basal nociception. Following in vivo loss of NRP1, mice are hyposensitive to both noxious heat and mechanical stimuli. Under normal conditions, VEGFA elicits mechanical hypersensitivity, an effect that was absent in our NRP1 knockout mouse. Furthermore, VEGFA induced neuronal hyperexcitability was lost in CGRP expressing neurons isolated from this NRP1 knockout mouse. This study validates the NRP1 knockout mouse and confirms previous findings that VEGFA, often released during pathological pain conditions, requires peptidergic NRP1. Interestingly, we find that in the absence of ongoing injury or inflammation, peptidergic NRP1 regulates basal nociception and pain-like behaviors. PerspectiveNRP1 is expressed in sensory neurons including the peptidergic subpopulation. Genetic deletion of NRP1 in healthy adults alters nociception without altering innervation; NRP1 knockout mice are hyposensitive to noxious heat and mechanical stimuli, but lose sensitivity to VEGFA, confirming it is a therapeutic target for growth factor mediated pain conditions.

Alzheimers disease (AD) is a neurodegenerative disorder affecting millions of patients globally. Despite significant efforts from researchers in recent decades, there are still many unanswered questions about AD pathogenesis. AD patient brains manifest changes in extracellular vesicles (EVs) secreted from diseased neurons, and the effect of this phenomenon remains poorly understood. EVs contain a variety of biomolecules and play a critical role in cell-to-cell communication in all eukaryotic organisms. Here, we report a thorough characterization of small EVs purified from cultures of human cerebrocortical organoids. These organoids are differentiated from human patient-derived stem cells that bear a familial AD mutation in the presenilin 1 (PSEN1) gene, or from an isogenic wildtype (WT) control. The organoid conditioned media was aspirated from cultures and processed for EV enrichment using a non-invasive technique that requires no cellular disruption. EVs purified from AD organoid conditioned media have a wider size distribution and show differential expression of tetraspanins CD63, CD9, and CD81 when compared to WT organoid-derived EVs. AD organoid-derived EVs can have single, double, and even triple membranes and display luminal fibrillar material. A deep proteomic profiling of the EVs reveals several statistically significant differences, including evidence for modifications in secretory autophagy. EV isolates from both WT and AD organoids show strong binding to amyloid detecting dyes, both in bulk fluorescence and fluorescence microscopy assays. After a 1-week co-culture of AD organoids with WT organoids, there is evidence of endosomal membrane transfer between the isogenic cultures with an increase in amyloid-{beta} peptides in the WT organoids. These observations support the notion that non-cell-autonomous spread of amyloid-containing EVs in human AD brains can be modeled in a cerebral organoid system.