Neuroscience

Valproic acid (VPA) is a widely used antiepileptic drug that also increases the risk of neurodevelopmental disorders in the offspring of exposed mothers. Prenatal exposure to VPA is a widely used rodent model of autism spectrum disorder (ASD). Anatomical, functional and molecular alterations in the retinas of various ASD model animals have been described in the literature, but the impact on the neural composition of the retina remains unclear. We examined whether and how the density and spatial regularity of selected retinal neurons are altered in the VPA induced model of ASD. Whole-mount retinas of 2-month-old VPA-treated and control animals were immunolabeled for S-cones, horizontal cells, AII amacrine cells, and parvalbumin-positive wide-field amacrines (PV-wfACs), and the positions of labelled cells mapped in various regions of interest (n = 39 for treated, n = 32 for control animals) across the retinas. Multivariate analysis of variance revealed a significant overall effect of VPA on cell densities (p = 6.1x10-7, 2 = 0.43), driven mainly by reduced AII amacrine density, while horizontal cells showed a modest reduction and S-cones were unaffected. After adjusting for retinal location, analysis of covariance indicated a 7% decrease in AII cells and a 15% increase in PV-wfACs. Regularity indices calculated from nearest neighbor distances or Voronoi-domain areas of cell mosaics were largely unchanged. These findings suggest that prenatal VPA exposure selectively alters inhibitory inner retinal circuitry in the rat ASD model at the time of cell differentiation, but self-organizing mechanisms responsible for spatial order are not affected. Lay SummaryValproic acid (VPA) is a medicine for epilepsy, but it can also raise the risk of autism in children when taken during pregnancy. In rats exposed to VPA before birth, we found changes in certain nerve cells of the retina: one type of cell important for night vision was reduced, while another type increased slightly, while most other cells stayed the same. This suggests that the changes in development that lead to autism may also be reflected in the structure and function of the eye.

Consumption of high fat diet (HFD) is linked to reduced cardiac vagal motor output, a main contributor to progression of cardiovascular disease. HFD for 15 days increases extrasynaptic or tonic gamma aminobutyric acid (GABA) current in cardiac projecting neurons in the dorsal motor nucleus of the vagus (CVNDMV), which contributes to dampening cardiac parasympathetic output. However, the mechanism underlying this increased inhibition is unknown. Here, we hypothesize that increased activity of protein kinase C {delta} isoform (PKC{delta}) enhances tonic GABA current in CVNDMV after HFD. Whole-cell patch-clamp recording of retrogradely labeled CVNDMV demonstrated that pan inhibition of PKC activity with GFX, and isoform specific inhibition of PKC{delta} with rottlerin normalize 15-day HFD-induced increases in tonic GABA current, suggesting that PKC{delta} mediates enhanced tonic inhibition. This effect persisted in the presence of dynasore, a clathrin-mediated endocytosis blocker, indicating that the normalization effect of PKC{delta} inhibition on tonic current in HFD is likely independent of clathrin-mediated endocytosis. Furthermore, no differences in PKC{delta} mRNA or protein expression were observed between NFD and HFD, suggesting a post-translational mechanism underpinning increased tonic GABA current after 15 days of HFD. Altogether, this study provides evidence that HFD-induces increased PKC{delta} activity, but not expression, leading to increased tonic GABAergic inhibition in CVNDMV. This increase PKC{delta} activity could explain the cardiac vagal motor output dampening in CVD and be developed into treatments targeting PKC{delta} for CVD.

Central nervous system injury causes motor deficits through derangement of excitatory, inhibitory, and/or neuromodulatory inputs to motoneurons, the three fundamental components of motor commands. Typically, study of pathologic neural control in humans is restricted to only one of the three. Chardon et al. (2024) presented a fundamentally new approach to comprehensively study all components by reverse engineering motor unit firing patterns. We apply their framework to motor unit firing patterns from 89 people with multiple sclerosis (MS) and 34 controls to study excitatory, inhibitory, and neuromodulatory contributions to pathologic motor output. Disruptions to all components are plausible in MS, a disease hallmarked by heterogeneity in nearly all aspects. Accordingly, we found abnormalities in MS for all three components. Notably, neuromodulation included both high and low extremes. Our results suggest that pathophysiology of motor commands in MS varies among patients, a finding fundamentally different from other studied populations showing relative consistency.

We recently reported that rats performed better at a task distance of 2 m than at 0 m in a T-maze delayed alternation paradigm using a movable home cage in the longer-delay condition (Takita & Ichitani, 2026). We simultaneously recorded local field potentials from the bilateral prefrontal cortex, intermediate hippocampus, and ventral hippocampus. Across task epochs, coherence and two cross-frequency measures (phase-locking value and modulation index [MI]) revealed differences between correct and error trials in prefrontal interactions with hippocampal subregions. Among these measures, only MI was affected by task distance during the pre-task delay epoch. MI was highest in 2-m error trials and lowest in correct trials. In 0-m error trials, MI transiently increased during arm entry to levels comparable to those in 2-m error trials before declining toward the levels observed in correct trials during the later post-task delay. These MI dynamics appeared to be consistent with distance-dependent differences in behavioral performance. In addition, normalized Correct-Error Indices calculated for each electrophysiological measure revealed differential contributions of prefrontal coupling with the intermediate and ventral hippocampus across task distances. These findings suggest the existence of distinct near and far working memory states underlying distance-dependent behavioral differences, with distinct yet complementary contributions of the intermediate and ventral hippocampus to prefrontal interactions.

The mechanisms of the spinal cord regeneration after complete spinal cord transection were investigated in spiny mice. In some animals, the appearance of quadrupedal overground stepping together with rewiring of the direct propriospinal projections between the cervical and lumbar enlargements was revealed. In others, no stepping recovery was detected, whereas numerous cells labeled by the neuronal proteins NeuN and {beta}III-tubulin were observed within the injury region. We suggest that depending on trauma severity, different repair mechanisms are elicited: only connectome restoration or both connectome restoration and the activation of neurogenesis. To confirm the high neurogenic potential of spiny mice, a primary culture of bone marrow was established. Unlike in other mammals, bone marrow pluripotent cells in the culture differentiated into neuronal cells without any chemical stimulation. These findings provide strong evidence for the high differentiation potential of spiny mouse stem cells toward neural lineages. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=180 SRC="FIGDIR/small/739224v1_ufig1.gif" ALT="Figure 1"> View larger version (73K): org.highwire.dtl.DTLVardef@1e6f2c1org.highwire.dtl.DTLVardef@14b88f6org.highwire.dtl.DTLVardef@ce5b5org.highwire.dtl.DTLVardef@bcebd9_HPS_FORMAT_FIGEXP M_FIG C_FIG HIGHLIGHTSO_LITwo regenerative mechanisms are proposed in spiny mice, depending on the severity the spinal cord transection C_LIO_LIRegular transection evoked the emergence of the direct propriospinal projections C_LIO_LISevere transection evoked the neurogenesis within the primary injured region C_LIO_LIPrimary culture of bone marrow cells from spiny mice exhibits neurogenic differentiation without chemical induction C_LI

Surface electromyography (EMG) studies have demonstrated anticipatory muscle activation prior to predictable voluntary actions. However, the mechanism through which this preparation is expressed, whether through motor-unit recruitment or discharge-rate modulation, remains to be elucidated. We employed surface decomposition EMG to quantify motor-unit behavior prior to self-paced rapid isometric elbow-flexion force pulses. Twelve healthy young men were instructed to generate elbow-flexion pulse force at 30%, 40%, and 50% of the maximal voluntary contraction (MVC) at a self-selected time. Motor-unit activity was decomposed from the biceps brachii and triceps brachii muscles, and the normalized active motor-unit number and mean discharge rate were analyzed prior to pulse onset. In the agonist, the pre-pulse increase mean discharge rate exhibited a higher value than the change in detected motor-unit count, particularly at the 40% and 50% MVC targets. The discharge-rate increase scaled with the target force, with a heightened response observed in high-threshold as compared to low-threshold motor units. Antagonist recordings with sufficient decomposition yield exhibited a similar discharge-rate-dominant pattern; however, these data were available from a smaller sample size. Present findings suggest that discharge-rate modulation is a primary motor-unit-level feature of anticipatory preparation for rapid isometric force production.

The ventral motor and the centromedian (CM) nuclei receive prominent GABAergic inputs from the basal ganglia, massive glutamatergic projections from motor cortices and significant GABAergic afferents from the reticular thalamic nucleus. There is strong evidence that disrupted processing of information through these connections may contribute to the pathophysiology of the basal ganglia-thalamocortical loop in Parkinson's disease (PD). To further assess potential ultrastructural changes in synaptic connectivity and mitochondrial integrity that may contribute to these network dysfunctions, we used a 3D electron microscopic approach to determine whether the pattern of synaptic innervation and morphological integrity of dendritic mitochondria are altered in the basal ganglia-receiving parvocellular ventral anterior nucleus (VApc) and CM neurons of MPTP-treated parkinsonian monkeys. Three main conclusions can be drawn from our findings: (1) Although the overall pattern of synaptic innervation of VApc and CM neurons is not altered in parkinsonian monkeys, the volume of putative corticothalamic terminals is significantly increased in both nuclei, (2) the prevalence of corticothalamic terminals in contact with distal dendrites is several orders of magnitude higher in VApc than CM in both control and parkinsonian monkeys, (3) the complexity and ultrastructural integrity of dendritic mitochondria is altered in CM, but not in the VApc, of parkinsonian monkeys. These findings lay the foundation for future studies of changes in cortical neuromodulation of VApc and CM neurons in parkinsonism and suggest that mitochondrial defects may contribute to the degeneration of CM neurons in PD.

The ability to accurately perceive arm position is essential for motor control and depends on the integration of proprioceptive and visual information. However, how lifelong visual impairment (VI) affects position sense and its neural correlates remains unclear. We quantified arm position sense and associated cognitive-motor load in right-handed visually impaired (n = 7) and normally sighted (NS; n = 7) individuals using three bilateral arm position matching tasks: joint angle matching (JAM; internal coordinates), hand direction-distance matching (DDM; external coordinates), and mirror direction-distance matching (MDDM; external coordinates kinematically identical to JAM). Cognitive load was assessed using the contingent negative variation (CNV) from EEG recordings. VI participants exhibited reduced accuracy and precision of arm position sense in most conditions, and greater CNV magnitude, particularly in the left parietal cortex. Across both groups, performance was worse and CNV magnitude was greater in the DDM task compared with JAM, whereas JAM and MDDM yielded similar behavioral and neural outcomes. These findings indicate that (i) visual experience enhances arm position sense, and (ii) representing limb position in external coordinates imposes greater cognitive demands than encoding joint-based posture. The similarity between JAM and MDDM suggests that participants preferentially rely on internal representations when task kinematics permit.

Cognitive processes rely on extensive thalamocortical and corticocortical recurrent interactions. The gamma frequency band ([~]40 Hz) of the electroencephalogram (EEG) emerges from these interactions. Importantly, cognitive processing depends on the interplay between bottom-up sensory inputs and top-down influences from higher-order cortical areas. However, the extent to which gamma-band oscillations are associated with directional patterns of functional interactions remains unclear. Therefore, the aim of this study was to investigate the directionality of gamma-band information flow during wakefulness (W) and sleep, under spontaneous conditions and in response to auditory stimulation. Cats were chronically implanted for polysomnographic recordings, with electrodes placed in multiple cortical and thalamic regions. Information-flow directionality was assessed using two complementary methods: (i) time-lag analysis of gamma-band amplitude envelopes between pairs of channels, and (ii) Granger Causality analysis of the same channel pairs. During quiet W gamma-band oscillations exhibited a predominantly top-down directional organization, from higher- to lower-order cortical areas, as well as from cortical regions to thalamic nuclei. Following auditory stimulation, a prominent gamma response emerged between 0.5 and 1.5 s after stimulus onset. Within this time window, distinct patterns of gamma-band information flow were observed depending on the nature of the stimulus. Specifically, a bottom-up directional predominance was observed for simple auditory stimuli (clicks), whereas top-down processing prevailed for complex variable stimuli. In contrast, no consistent directionality of information flow was observed during either NREM or REM sleep, regardless of whether auditory stimulation was present. These findings extend our understanding of gamma-band information-flow dynamics during wakefulness and sleep.

Research suggests that motor difficulties in Developmental Coordination Disorder (DCD) are related to altered motor sequence planning, but it is unclear which mechanisms are affected, particularly in adults. This study addresses that gap by examining how the order of upcoming movements during the planning of skilled typing sequences affects motor production in adults with DCD. Previous monkey neurophysiology and behavioural findings in humans have shown that elements of a sequence are pre-ordered prior to execution, known as competitive queuing (CQ). CQ quality is predictive of subsequent performance, with skilled performers, those with fewer errors, having a larger position-dependent difference. DCD (N=28) and control participants (N=54) performed two 4-element finger sequences from memory in a delayed sequence production task over 3 sessions. Probe trials, which involved participants performing a single press after the Go Cue, assessed motor planning at each sequence position by measuring reaction time (RT) and error rate. We found that adults with DCD had a higher error rate and were slower to initiate and perform correct sequences. In terms of planning, the DCD group showed reduced preordering of sequence elements. Whilst the DCD group had a higher error rate on a working memory task, this was not correlated with the degree of pre-ordering of presses of the upcoming sequence. These findings suggest that disrupted motor sequence planning in DCD is characterised specifically by a failure to pre-order movements during the retrieval of sequences from memory. Additionally, motor sequence pre-ordering deficits in DCD are independent of general working memory impairments. These results extend prior evidence from motor imagery paradigms, demonstrating that internal modelling deficits are evident during the execution of motor plans. HighlightsO_LIAdults with DCD show diminished pre-ordering of sequential movements during planning. C_LIO_LIThe DCD group were slower to initiate and perform correct sequences from memory. C_LIO_LIMotor sequence planning is distinct from working memory performance. C_LIO_LIThis provides evidence for the IMD hypothesis in a skilled sequential task. C_LI

Abstract Background: Long COVID frequently includes post-exertional malaise, neuromuscular fatigue, internal vibrations, tremor-like symptoms, orthostatic intolerance, sleep disturbance, cognitive dysfunction, and autonomic instability. Neuroimaging studies in Long COVID and post-infectious ME/CFS have identified abnormalities across limbic, thalamic, mesiotemporal, brainstem, cerebellar, and white-matter systems, but no single established circuit accounts for this clinical phenotype. We examined whether abnormalities cluster at the mammillary body-fornix-superior tuberal hypothalamic interface and within connected brainstem-cerebellar pathways. Methods: Structural MRI and diffusion tensor imaging were analysed in 88 participants with clinician-diagnosed Long COVID and 34 healthy controls (total N = 122). Thirty-three patients were classified as bedridden. Volumetric and diffusion analyses focused on the mammillary bodies, superior tuberal hypothalamic region, fornix, dorsal and median raphe, midbrain reticular formation, and cerebellar peduncles. Fractional anisotropy was used as an index of white-matter microstructural organisation. Exploratory clinical associations included motor impairment, proprioceptive dysfunction, autonomic symptoms, fatigue, internal vibrations, and tremor-like symptoms. Results: Three mammillary-body volume phenotypes were identified: reduced, enlarged, and control-range. Left and right mammillary-body volumes differed across groups, with large effect estimates. Segmentation showed narrowing or loss of a visible internal passage at the superior tuberal-mammillary interface, while the fornix showed altered diffusion measures and reduced tract coherence in the hypothesised gate region. Additional findings included lower superior cerebellar peduncle volume, lower middle cerebellar peduncle fractional anisotropy, and lower dorsal raphe and midbrain reticular formation volumes in Long COVID. Conclusions: The findings support an exploratory mammillary body-fornix gate model in which a vulnerable periventricular hypothalamic-limbic interface may contribute to network dysfunction in a subgroup of patients with severe Long COVID. The data do not establish direct viral invasion, a coronavirus entry route, axonal destruction, or a single causal pathway. Prospective replication with standardised acquisition, preregistered regions of interest, correction for multiple comparisons, objective movement and autonomic measures, and longitudinal follow-up is required. Keywords: Long COVID; post-COVID condition; ME/CFS; mammillary body; fornix; hypothalamus; diffusion tensor imaging; internal vibrations; tremor-like symptoms; neuromuscular fatigue; dysautonomia; brainstem

It is well documented that both motoneuron output and the effectiveness of activated Ia afferents to discharge soleus -motoneurons decrease during eccentric (muscle lengthening) contractions. Evidence suggests that these modulations can be explained by recurrent inhibition and greater presynaptic inhibition of Ia afferents. However, the influence of angular velocity on the modulation of the effectiveness of activated Ia afferents to discharge -motoneurons observed during eccentric contractions remains unclear. We investigated the influence of angular velocity on spinal mechanisms involved in the effectiveness of activated Ia afferents to discharge -motoneurons during eccentric plantar flexor contractions using 16 healthy adults. We used both simple and conditioned Hoffmann reflex with different conditioning techniques to assess presynaptic inhibition, heteronymous Ia facilitation and heteronymous recurrent inhibition coupled with electromyography during eccentric contractions of the plantar flexors at three angular velocities. Our results showed that during eccentric contractions, the effectiveness of Ia afferents to discharge -motoneurons was lower at 90{degrees}{middle dot}s-{superscript 1} than 60{degrees}{middle dot}s-{superscript 1} and 20{degrees}{middle dot}s-{superscript 1} angular velocities. A similar velocity-dependent pattern was observed for heteronymous recurrent inhibition, decreasing at 90{degrees}{middle dot}s-{superscript 1} when compared with 60{degrees}{middle dot}s-{superscript 1} and 20{degrees}{middle dot}s-{superscript 1}. In contrast, presynaptic inhibition of Ia afferents was not different between the velocities. These demonstrate a differential influence of angular velocity on spinal recurrent inhibitory mechanisms during eccentric contractions and support distinct functional roles of recurrent and presynaptic inhibition in modulating -motoneurons discharge with increasing movement velocity. The findings provide new insights into the velocity-dependent and mechanism-specific modulation of spinal inhibitory circuits during eccentric contractions. KEY POINTSO_LIDuring eccentric contractions in soleus muscle, the effectiveness of activated Ia afferents to discharge -motoneurones decreases with increasing angular velocity, indicating a velocity-dependent modulation. C_LIO_LIPresynaptic inhibition of Ia afferents does not differ between angular velocities, suggesting that it does not contribute to the observed changes. C_LIO_LIHeteronymous recurrent inhibition from the quadriceps to the soleus increases with angular velocity, indicating that increasing movement velocity promotes a functional reorganization of intermuscular recurrent inhibition. C_LIO_LIThese findings suggest a differential functional role of the two spinal inhibitory mechanisms, indicating that increasing angular velocity primarily influences recurrent postsynaptic inhibition rather than presynaptic inhibition. C_LI

Stress-related experiences alter glutamatergic signaling and neuronal excitability, but the mechanisms that couple experience to dentate granule cell function remain incompletely understood. Here, we examined how protein kinase N1a (PKN1a), a protein kinase C-like serine/threonine kinase, and repeated swim exposure regulate mouse hippocampal dentate granule cell excitability, with a focus on the neuronal glutamate transporter excitatory amino acid transporter 3 (EAAT3) and group I metabotropic glutamate receptors (mGluRs). Five days of repeated swim exposure increased spike firing in mature dentate granule cells from wild-type mice. PKN1a knockout produced a similar increase, and repeated swim did not further enhance firing in knockout mice. The enhanced firing observed after repeated swim exposure and in PKN1a knockout mice was reduced by co-application of an mGluR1 antagonist (LY367385) and an mGluR5 antagonist (MPEP). Inhibition of glutamate transporters with DL-TBOA increased granule cell firing in control wild-type mice but did not further increase firing in repeated-swim wild-type or PKN1a knockout mice, suggesting occlusion of transporter-dependent regulation of excitability. Repeated swim exposure and PKN1a knockout also reduced total and surface expression of EAAT3 in the hippocampus, whereas expression of the glial glutamate transporter EAAT2 was not significantly altered. Finally, PKN1a knockout and repeated swim exposure reduced anxiety-related behavior in the elevated plus maze test. Thus, PKN1a-dependent regulation of EAAT3 may restrain group I mGluR-dependent excitability in dentate granule cells, whereas repeated swim exposure and PKN1a knockout shift this system toward a lower-EAAT3, higher-excitability state accompanied by reduced anxiety-related behavior.

The pelvic floor muscles (PFM) are critical for maintaining continence and are a primary target of physiotherapy training to manage urinary incontinence. PFM training relies on voluntarily activating this muscle group, limiting its translation to neurological populations where recovery of bladder function is a priority. Indirect evidence suggests that sensory feedback from the lower limb can modulate PFM activity, which may provide alternative strategies for PFM training. Cutaneous reflexes have been used as a proxy to study how sensory inputs from the skin influence motoneuron excitability. To explore the feasibility of eliciting cutaneous reflexes in the PFM and their role in controlling PFM activity, this study examined: 1) the input-output relationship and 2) the nerve-specificity of PFM cutaneous reflex responses from tibial and superficial peroneal nerve stimulation. Twenty-one neurologically intact adults participated in this study. We recorded PFM and lower leg muscle electromyography while participants received cutaneous stimulation to the right distal tibial nerve, bilateral distal tibial nerve, or right superficial peroneal nerve in a standing position. We delivered stimulation at the intensity below motor threshold (MT), 1.2 x MT and 1.5 x MT and quantified tibial-PFM reflex amplitude over a 50-150 ms window after stimulation. PFM reflex responses were evoked from both nerves stimulation. Reflex amplitude increased with stimulus intensity with tibial nerve stimulation but not with superficial peroneal nerve stimulation. Bilateral tibial nerve stimulation evoked larger responses compared to unilateral stimulation. These findings support the existence of neural connections between lower limb afferents and the PFM, and open up possibilities for designing rehabilitation strategies to manage pelvic health conditions in people with neurological disorders. New & NoteworthyO_LICutaneous sensory feedback from the foot, specifically that related to limb loading, can evoke reflex responses in the pelvic floor muscles C_LIO_LINerve-specific modulation was observed. Reflex amplitudes in the pelvic floor muscles increased with tibial nerve stimulation intensity but not with superficial peroneal nerve stimulation. C_LI

Queuosine (Q) modification is a hypermodified nucleoside derived from guanine on tRNAs that enhances the decoding of codons and equilibrates translational speed. Q is biosynthesized in bacteria, and eukaryotes salvage Q and the nucleobase queuine from the diet and the gut microbiome. In animals, Q deficiency causes impaired proteostasis, mitochondrial dysfunction, and neurological phenotypes, possibly due to the longevity and high metabolic demand of neurons. Yet, how Q affects isolated neurons has not been explored yet. Here, primary rat cortical neurons were cultured in Q-free synthetic medium to directly modulate Q modification levels independently of genetic perturbation, enabling assessment of its effects on neuronal development, survival, morphology, synaptic organization, and activity. Importantly, we found that the presence of Q modification facilitated neuronal arborization, decreased inhibitory synaptic density, and increased the frequency of spontaneous calcium transients, showing that tRNA Q modification enhances neuronal structural maturation and synaptic activity. Thus, the fine-tuning of neuronal translation programs by Q-tRNAs is required for proper network development and may influence neuronal resilience and synaptic function.

Sympathetic preganglionic neurons (SPNs) provide the sole spinal output to the peripheral sympathetic nervous system. Although sympathetic control is traditionally attributed to synaptic integration within the spinal cord and ganglia, the reliability of spike propagation along SPN axons themselves has received little attention. Here, and in companion papers, we show that axonal conduction in adult mouse thoracic SPNs is highly modifiable and constitutes a critical site of sympathetic gain control. Using an ex vivo preparation preserving intact paravertebral and splanchnic pathways while blocking synaptic transmission, we recorded compound action potentials evoked across multiple ganglia. Slower-conducting, unmyelinated SPN axons, particularly those with branching axons traversing the interganglionic nerve (IGN), exhibited pronounced, temperature-dependent conduction failures. Elevation of temperature produced membrane hyperpolarization and loss of conduction, consistent with activation of temperature-sensitive K2P leak channels, as supported by pharmacological evidence. Pharmacological activation of TREK-family channels with riluzole or arachidonic acid preferentially suppressed conduction in these axons. In contrast, blockade of voltage-gated K+ channels with 4-aminopyridine (4-AP) robustly facilitated conduction, recruited previously silent axons, and restored propagation under conditions of temperature-induced failure. Surprisingly, tetraethylammonium (TEA) block of K+ channels were without effect or depressant. Transmitter systems further shaped axonal reliability: agonists and antagonists of GABAA receptors, as well as cholinergic manipulations, selectively depressed conduction in slow, branching axons. Together, these findings establish SPN axons, particularly slow-conducting branching fibers, as an active and dynamically regulated substrate for sympathetic output control, revealing a presynaptic mechanism with implications for autonomic physiology and disease. SIGNIFICANCESympathetic output is commonly viewed as being regulated primarily through synaptic integration within spinal and autonomic circuits, while axons are often treated as passive transmission elements. Emerging evidence suggests this assumption is incomplete, particularly in slowly conducting and highly branched sympathetic preganglionic neuron (SPN) axons that may operate near the limits of conduction reliability. This study identifies branch point conduction as a dynamic and pharmacologically modifiable control mechanism governing sympathetic signal transmission. By demonstrating selective vulnerability of distinct SPN populations and revealing strong modulation by potassium channel mechanisms, these findings establish axonal conduction security as an underappreciated site of autonomic gain control. These mechanisms may represent novel therapeutic targets for restoring autonomic function after spinal cord injury and related disorders.

Astrocytes play an important role in neuronal health. A critical function of astrocytes is to clear excess extracellular glutamate and prevent excitotoxicity. STAT3 is a transcription factor that promotes astrocyte development and astrocyte reactivity in neurodegenerative diseases and following central nervous system injury. To determine the innate molecular and behavioral functions of adult astrocyte-expressed STAT3 in a non-pathological state, we created conditional Stat3 astrocyte knockout mice (Stat3 aKO) using Stat3flox and the tamoxifen-activated Cre line, Aldh1l1-Cre/ERT2. We measured transcript levels of Gfap, a known STAT3 target gene, and glutamate transporter genes in the medial prefrontal cortex (PFC) of Stat3 aKO. Gfap, Slc1a2 and Slc17a8 transcripts were decreased in the PFC of Stat3 aKO of both sexes. GLT-1 protein, encoded by Slc1a2, was also reduced in the PFC of male Stat3 aKO. We recorded spontaneous excitatory post-synaptic currents (sEPSCs) in male Stat3 aKO and control prelimbic pyramidal neurons and found increased sEPSC amplitude, consistent with a hyper-glutamatergic state due to impaired glutamate clearance. To determine the behavioral consequences of STAT3 depletion in astrocytes, Stat3 aKO were tested for locomotor activity, anxiety-like behavior and binge ethanol consumption, behaviors linked to dysregulation of glutamate homeostasis. Stat3 aKO mice did not differ in locomotor activity or anxiety-like behavior; however, male Stat3 aKO mice consumed significantly less ethanol than controls. These results indicate that STAT3 in adult astrocytes is crucial for maintaining glutamate transporter levels in the adult brain and that astrocytic STAT3 promotes ethanol consumption in male mice. Main pointsO_LIGfap, Slc1a2 and Slc17a8 expression are lower in the cortex of Stat3 astrocyte knockout mice (Stat3 aKO) C_LIO_LIGLT-1 protein is decreased and glutamate neurotransmission is elevated in the cortex of male Stat3 aKO C_LIO_LIMale Stat3 aKO consume less ethanol C_LI

Neurodegeneration is a major determinant of disability progression in multiple sclerosis (MS), yet the pathophysiological mechanisms associating inflammation to neuronal insult remain poorly understood. We recently identified Dendritic Syntaphilin Intrusion (DSI), a novel excitoxicity pathway in which the axonal mitochondrial anchor syntaphilin (SNPH) aberrantly translocates into dendrites, causing neurodegeneration in a non-inflammatory model of MS. However, whether this protein intrudes abruptly into dendrites in inflammatory MS pathology is still not clear. Here, we investigated the role of synaptic and extrasynaptic NMDA receptors (NMDAR) in regulating the intrusion of Syntaphilin into dendrites. Using primary hippocampal neuronal cultures, we examined how the balance between synaptic GluN2A-containing and extrasynaptic GluN2B-containing NMDARs influences DSI under inflammatory conditions. Pharmacological and viral-mediated approaches were employed to manipulate NMDAR subtype activity and evaluate their impact on DSI. Inflammatory cytokines discernibly sensitized neurons to DSI. Our results revealed that blockade of synaptic NMDARs significantly increased DSI, whereas inhibition of extrasynaptic NMDARs reduced DSI. These findings demonstrate opposing roles of NMDAR subtypes, with GluN2A-containing synaptic receptors inhibiting DSI and fostering neuronal survival, while GluN2B-containing extrasynaptic receptors enhancing DSI and neurodegenerative signaling. Manipulation of the GluN2A/GluN2B balance showed opposite effect on DSI, suggesting a relationship between NMDAR subtype signaling and SNPH mislocalization. Overall, our findings extend the relevance of DSI from non-inflammatory MS to inflammatory MS and identify DSI as a downstream convergence point linking inflammatory cytokines and excitotoxic NMDAR signaling to neuronal insult. These results reveal DSI as a potential mechanistic link between inflammatory signaling and excitotoxic neuronal injury and indicate that modulation of GluN2B-dependent pathways warrants further investigation in inflammatory neurodegenerative disorders.

Long-latency stretch reflex and corticospinal excitability in the tibialis anterior muscle (TA) are facilitated when balance is threatened, even without background TA activity, suggesting supraspinal modulation as preparatory tuning for ankle stabilization. However, it remains unclear whether such tuning is evident at the spinal level and specific to the TA among lower-limb muscles. We therefore examined the effects of height-induced postural threat on multi-segmental monosynaptic spinal reflexes (MMR) in lower-limb muscles during quiet standing. Seventeen healthy young males performed 90-s standing tasks under three postural threat conditions, created by combining real and virtual reality (VR) heights: (1) Low-threat (real ground & VR ground), (2) Medium-threat (real table & VR ground), and (3) High-threat (real table & VR bridge). During each condition, transcutaneous spinal cord stimulation (tSCS) was applied to the lumbar spine to elicit MMR in lower-limb muscles. Electromyograms (EMG) were recorded from six muscles of the right leg: vastus medialis (VM), biceps femoris (BF), TA, soleus (SOL), medial (MG), and lateral gastrocnemius (LG). MMR excitability was quantified as peak-to-peak EMG amplitude. Fear ratings and electrodermal activity were higher in High-threat than Low-threat (all p < 0.05), confirming successful threat induction. Peak-to-peak EMG amplitude in the TA was significantly higher in High-threat than Low-threat (17.1% increase, p = 0.0393), whereas background TA activity remained absent across conditions. These results indicate that TA has unique function to facilitate spinal excitability as a preparatory tuning for ankle stabilization. Key pointsO_LIPrevious studies have shown the supraspinal facilitation of the tibialis anterior muscle without background muscle activation as a preparatory tuning for ankle stabilization. C_LIO_LITo test the hypothesis that such tuning is also evident at the spinal level and specific to the tibialis anterior muscle, this study examined whether height-induced postural threat modulates multi-segmental monosynaptic reflex excitability in lower-limb muscles using transcutaneous spinal cord stimulation. C_LIO_LIElectrodermal activity and fear ratings increased under height-induced postural threat, confirming the successful induction of postural threat. C_LIO_LIUnder height-induced postural threat, the multi-segmental monosynaptic reflex was selectively facilitated in the tibialis anterior muscle, while its background activity remained absent. C_LIO_LIOur findings demonstrate selective facilitation of spinal excitability in the tibialis anterior muscle, which may serve as preparatory tuning for ankle stabilization under threat to balance. C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=147 SRC="FIGDIR/small/742625v1_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@ca21f3org.highwire.dtl.DTLVardef@7b1679org.highwire.dtl.DTLVardef@1007191org.highwire.dtl.DTLVardef@1ff88a_HPS_FORMAT_FIGEXP M_FIG C_FIG Abstract figure legendWhen balance is threatened, corticospinal excitability and long-latency stretch reflex in the tibialis anterior muscle (TA) are facilitated even in the absence of background TA activity, suggesting supraspinal preparatory tuning for ankle stabilization. This study tested the hypothesis that such facilitation is also expressed at the spinal level and is specific to the TA. Participants completed 90-s quiet standing trials under three different height-induced postural threat conditions. During each trial, transcutaneous spinal cord stimulation was delivered over the lumbar spine to elicit multi-segmental monosynaptic reflexes (MMR) in multiple lower-limb muscles. High-threat condition increased fear ratings and electrodermal activity, indicating successful threat induction. Moreover, MMR excitability was selectively increased in the TA under High-threat condition despite the absence of background TA activity. These findings suggest that spinal facilitation is selectively expressed in the TA and may reflect preparatory tuning for ankle stabilization under threat to balance.

Early-life adversity durably alters neural development through complex mother-offspring interactions whose underlying mechanisms remain poorly understood. We investigated how neonatal maternal separation (NMS) affects the large repertoire of maternal behaviors and subsequently influences spinal nociceptive circuit development and pain responses in rat offspring. Rat dams underwent NMS from postnatal day 2 (P2) to P12, 3h/day, and maternal behaviors were assessed before and after the separation period. These behaviors were compared to those of control (non-separated) dams. Offspring spinal cord and dorsal root ganglia were analyzed at P14 and P24 for several neurotrophic, glutamatergic, and GABAergic gene expression patterns. Offspring nociceptive sensitivity was also assessed at P24. NMS induced increased maternal behaviors (including longer arched-back nursing, higher nest occupancy, and better pup retrieval efficiency), alongside reduced self-care behaviors. These behavioral adaptations were correlated with spinal gene reprogramming in offspring, characterized by a biphasic developmental pattern. At P14, we observed elevated neurotrophic signaling alongside increased GABAergic and glutamatergic markers. By P24, neurotrophic factors decreased while compensatory changes emerged, yet persistent excitatory-inhibitory imbalances remained evident. Parallel to these results, NMS rats also showed mechanical and thermal hot hypersensitivity at P24. These findings reveal that despite apparent maternal behavioral compensation following NMS, offspring exhibit neurotrophic-driven developmental dysregulation resulting in persistent spinal circuit alterations. The disconnect between maternal behavioral normalization and sustained molecular changes suggests that early separation stress triggers enduring neurobiological cascades independent of ongoing maternal care quantity, with long-term consequences for sensory processing and pain sensitivity.