Brain Research

Dorsal (PMd) and ventral (PMv) premotor cortices can modulate contralateral primary motor cortex (M1) excitability, but their distinct interhemispheric influence via transcranial magnetic stimulation (TMS) remains unclear. Single-pulse TMS over PMd, PMv and M1 assessed transcallosal inhibition via the ipsilateral silent period (iSP). Dual-site TMS examined short-(10 ms inter-stimulus interval [ISI]), long-(50 ms ISI) and non-callosal-(0 ms ISI) interhemispheric inhibition (IHI). An iSP was elicited from PMd, PMv, and M1, with distinctly evoked iSP parameters. The iSP magnitude was greatest from M1, followed by PMd and then PMv, while iSP duration was greatest for M1 and showed no differences between PMd and PMv. Dual-site TMS revealed that PMd and M1 inhibited contralateral M1 excitability across all ISIs, while PMv showed inhibition at 0-and 50-ms ISIs. PMd and M1 demonstrated greater short-IHI compared to PMv, all demonstrating similar long-IHI, and PMd demonstrating greater non-callosal-IHI than M1. PMv displayed distinct IHI across ISIs, PMd showed differences across most ISIs and M1 demonstrated the fewest differences across ISIs. Longer iSP duration related to greater long-IHI magnitude elicited from PMd and PMv. Our findings demonstrate differential IHI from PMd and PMv on contralateral M1, which may inform neuromodulation strategies in rehabilitation contexts.

Emerging preclinical and clinical evidence suggests that low frequency hemodynamic oscillations drive CSF flow, which in turn mediates glymphatic clearance. The current study investigated whether CO2-induced low frequency hemodynamic oscillations during magnetic resonance imaging would increase clearance of proteins (glial fibrillary acidic protein, neurofilament light chain, ptau217 and brain-derived tau) from brain to blood, and temporarily improve cognitive performance in individuals with chronic traumatic brain injury (TBI) and age/sex-matched healthy controls. Results indicated that cerebrovascular reactivity, normalized CSF volume, and predicted brain age significantly differed between chronic TBI and controls, while bulk CSF flow differed only at trend levels. Multiple protein concentrations were significantly increased at [~]45 minutes post-hypercapnia, decreased at [~]90 minutes, and returned to pre-hypercapnia levels by [~]150 minutes. Protein efflux was more strongly associated with total CSF volume and total white matter volume rather than cerebrovascular reactivity or bulk CSF flow. Both groups exhibited reduced cognitive interference post-hypercapnia, and hypercapnia associated symptoms quickly returned to baseline levels. In conclusion, hypercapnia temporarily increases clearance of multiple neural abundant proteins into blood, and this effect is moderated by atrophy. Current results suggest that hypercapnia may therapeutically combat pathological protein aggregation post-trauma, and prophylactically during normal aging.

BackgroundMicroglial heterogeneity is a fundamental feature of brain homeostasis and pathology. The purpose of this study was to investigate the complexity of microglial plasticity by characterizing specialized oligodendrocyte-like microglial subsets. MethodsThe study was performed utilizing single-cell transcriptomics analyses and immunofluorescence staining to identify and profile microglial subpopulations. Additionally, spatial transferring and morphological analyses were conducted to determine the anatomical distribution and structural features of these specific cells. ResultsWe identified a distinct microglial subset termed dual-phenotype microglia (DPM), which co-expresses microglial and oligodendrocyte markers. DPM consisted of two subtypes with distinct functions: myelin-associated DPM (mDPM) and neuron-associated DPM (nDPM). Spatial and morphological evaluations revealed that mDPMs were sparsely distributed across the whole brain and exhibited a highly ramified architecture, whereas nDPMs were enriched in the hippocampal dentate gyrus. Mechanistically, we found that mDPM function was driven by the Sox10 regulon to modulate myelin maintenance and axonal ensheathment, while nDPM was orchestrated by Glis2, facilitating essential neuron-glia crosstalk and synaptic regulation. Furthermore, we demonstrated that nDPM and mDPM were predicted to undergo significant alterations in multiple sclerosis and Alzheimers disease. Notably, mDPMs were selectively enriched in active multiple sclerosis lesions, revealing that DPM were closely related to neuropsychiatric disorders. ConclusionsBy comprehensively characterizing the morphology, molecular signatures, and spatial logic of these oligodendrocyte-like microglial subsets, our study elucidated the complexity of microglial plasticity. These findings provided new insights into their diverse roles in central nervous system health and disease. Graphical abstractIdentification, Molecular Profiling, and Functional Modeling of Dual-Phenotype Microglia (DPM). (1) Discovery: Identification of the dual-phenotype microglia (DPM) population through single-cell transcriptomics. (2) Molecular Signatures: The transcriptomic identity of DPM subtypes is governed by specific regulatory networks. (3) Distribution & Pathology: Spatial mapping reveals divergent anatomical logic and disease relations for DPM subtypes. (4) Mechanism/Theory: A proposed functional model of mDPMs as "metabolic relay" and support units. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/724239v2_ufig1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@b7db1dorg.highwire.dtl.DTLVardef@9265e7org.highwire.dtl.DTLVardef@1605d82org.highwire.dtl.DTLVardef@19b048f_HPS_FORMAT_FIGEXP M_FIG C_FIG

Microglia are the brains resident immune cells that exhibit complex signaling behavior, including phagocytic activity in response to threats and prolonged neuronal activity. Adenosine triphosphate (ATP) is a chemoattractant for microglia. In the nucleus accumbens (NAc), ATP is co-packaged and released with DA, and microglia express dopamine (DA) receptors and ATP receptors. The present work examines microglia chemotactic motility for these transmitters using iontophoresis and multiphoton microscopy approaches in NAc brain slices from GFP-monocyte labeled transgenic mice. ATP chemoattraction was more regularly observed than DA chemoattraction, and DA chemoattraction occurred in only a small subset of microglia. The DA chemoattraction of this subset was blocked by DA D1 antagonism. Microglia are reactive oxygen species (ROS) scavengers. Application of glucose oxidase produces mild but consistent increases in ROS and induced inflammatory-related changes in microglial morphology and motility. Glucose oxidase application decreased DA release but had variable effects on ATP release. The toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS) transitioned microglia from ramified to amoeboid morphology over a period of 4 hours, and increased DA and ATP release across this same period. These studies highlight the complex relationship between local immune activation and DA terminal functionality.

Elite athletes exhibit sport-specific neural adaptations, yet it remains unclear whether such changes reflect general effects of training or the unique demands of individual sports. Skiing requires postural control and whole-body coordination under dynamically unstable environments, placing high demands on somatosensory processing and sensorimotor integration. The present study aimed to identify structural brain characteristics specific to elite skiers by comparing them with athletes from other sports disciplines and non-athletes. T1-weighted MRI data were analyzed using voxel-based morphometry in 13 skiers, 23 non-ski control athletes and 25 non-athletes. Whole-brain analysis comparing skiers with non-ski athletes revealed a significant cluster showing greater gray matter volume in skiers compared with non-ski athletes in the left postcentral gyrus, extending into the superior parietal lobule. The identified cluster primarily encompassed cytoarchitectonic Areas 2 and 5L. These regions are involved in higher-order somatosensory processing and multisensory integration. Importantly, region-of-interest analysis demonstrated that gray matter volume within this cluster was greater in skiers compared with non-ski athletes and non-athletes, with no difference between non-ski athletes and non-athletes. These findings highlight the relative prominence of structural adaptations within somatosensory-parietal networks, reflecting the unique integration of proprioceptive and other sensory information required for elite skiing. Overall, these findings provide evidence for sport-specific structural brain differences in elite athletes and highlight the importance of somatosensory and parietal regions in sensorimotor integration relevant to skiing. These findings may have implications for understanding neural markers of expertise and may inform future approaches to training and performance evaluation in skiing.

Serotonin is one of the main neuromodulators in the brain, involved in regulating mood, complex behaviors and sensory input. Serotonin reaches primary somatosensory cortex (S1) via axons of neurons located in the dorsal raphe nucleus (DRN). DRN neurons can be modulated, amongst others, by reward, sensory stimulation, or movement but the activity pattern of serotonergic neurons targeting S1 is not known. Therefore, it is unclear under which circumstances serotonin is released in S1. Here, we expressed GCaMP8 in serotonergic neurons of the DRN to analyze the activity of their axons in S1 using two-photon Ca2+-imaging. Cluster analysis of axonal activities suggests that one to four functional groups of serotonergic axon segments project to a 0.3 mm2 horizontal plane of S1. We show that activity in serotonergic axons is strongly driven by reward and weakly by sensory stimulation of the whiskers. Movement, however, is preceded by a modulation, up and down, of the serotonergic signal seconds before the running onset. In summary, rewards and sensory stimulation lead to activity in serotonergic axons which is likely to adjust signal processing in S1 upon these events. The serotonergic signal changes seconds before movement onset probably preparing the neural network in S1 for the state change that accompanies running.

Background/ObjectivesNeuroinflammation-driven iron dysregulation and neurotoxic astrocyte polarization are increasingly recognized as interconnected pathological mechanisms in neurodegenerative diseases. Systemic inflammation triggered by strenuous exercise or infection can engage the central nervous system and astrocytic inflammatory responses and perturb iron homeostasis; however, targeted nutritional strategies to counteract these processes remain limited. Inflamate(R) is a multi-component botanical supplement comprising boswellic acids, astilbin, xanthohumol, and cinnamaldehyde, each with documented anti-inflammatory properties. However, whether this combined formulation can modulate the inflammatory-iron metabolic axis and astrocyte phenotypic polarization remains unexplored. This study aimed to investigate the effects of Inflamate(R) on LPS-induced pro-inflammatory gene expression, iron metabolism-related gene regulation, and A1/A2 astrocyte phenotypic polarization in mouse astrocytes. MethodsMouse astrocytes (AWT) were pre-treated with Inflamate(R) (0.0375 g/mL) or DMSO vehicle for 24 h, followed by lipopolysaccharide (LPS; 1 g/mL) stimulation for an additional 24 h. The non-cytotoxic working concentration was determined by morphological assessment, CCK-8 cell viability, and LDH cytotoxicity assays. Expression of 14 target genes spanning pro-inflammatory mediators (NOS2, IL6, C3, COX2, PLA2g15, SOCS3), iron metabolism regulators (FTH1, Hepcidin, TFRC, SLC40A1, RGMa, RGMb), and astrocyte polarization markers (S100A10, GFAP) was quantified by qRT-PCR. ResultsUnder normal culture conditions, Inflamate(R) did not significantly alter the expression of any target gene except S100A10, confirming the absence of baseline cytotoxicity or transcriptional homeostatic perturbation. Upon LPS stimulation, Inflamate(R) selectively suppressed NOS2 (approximately 64% reduction, p < 0.0001), IL6 (approximately 37% reduction, p < 0.0001), and C3 (approximately 47% reduction, p < 0.0001), while COX2, PLA2g15, and SOCS3 remained unaffected. Concurrently, Inflamate(R) significantly reduced LPS-induced Hepcidin expression to approximately 17% of the control level (p < 0.05) and attenuated FTH1 upregulation (p < 0.01), without altering the expression of iron transporters (TFRC, SLC40A1) or BMP-SMAD pathway components (RGMa, RGMb). Furthermore, Inflamate(R) upregulated the neuroprotective A2 marker S100A10 under both basal (p < 0.05) and LPS-stimulated conditions (p < 0.01), while the general reactivity marker GFAP remained unchanged. ConclusionsInflamate(R) exerts a selective, multi-target modulatory effect at the transcriptional level in LPS-stimulated astrocytes, encompassing suppression of the iNOS-NO and IL-6 signaling axes, attenuation of inflammation-driven hepcidin-ferritin iron dysregulation via the IL-6-STAT3 pathway, and promotion of a phenotypic shift from neurotoxic A1 toward neuroprotective A2 astrocyte polarization. Given that the IL-6-JAK-STAT3-hepcidin axis is also activated during exercise-induced systemic inflammation, these findings suggest that Inflamate(R) may represent a targeted nutritional strategy for preserving CNS iron homeostasis and supporting neuroprotective astrocyte function in both neurodegenerative and exercise-related neuroinflammatory contexts. Further validation in in vivo neurodegenerative and exercise models, including protein-level analyses, is warranted to confirm these transcriptional findings.

Voluntary contraction in one limb can facilitate motor output in a distant limb, a phenomenon commonly referred to as the remote effect. However, the neural mechanisms underlying this remote interlimb facilitation remain unclear. This study investigated cortical and spinal contributions to the remote effect in able-bodied participants. Transcranial magnetic stimulation (TMS) was applied over the hand area of the primary motor cortex using posterior-anterior (PA) and anterior-posterior (AP) current directions, which are sensitive to different cortical inputs. Cortical excitability was assessed using single- and paired-pulse paradigms to measure short-interval intracortical inhibition (SICI), short-interval intracortical facilitation (SICF), and short-latency afferent inhibition (SAI). Spinal motoneuron excitability was assessed from F-waves elicited by peripheral nerve stimulation. During voluntary lower-limb contractions, single-pulse TMS elicited larger motor evoked potentials in hand muscles across current directions, indicating a broad increase in net corticospinal output. However, only AP-sensitive paired-pulse measures showed reduced SICI and enhanced SICF during contraction, whereas PA-sensitive SICI and SICF were not significantly altered, suggesting that cortical modulation during the remote effect is expressed more clearly in AP-sensitive measures. SAI with PA stimulation was less consistently expressed during contraction, suggesting that afferent-related inhibitory modulation may also be influenced during the remote effect. In parallel, F-wave amplitude and persistence increased, consistent with enhanced spinal motoneuron excitability. Together, these results provide converging evidence that the remote effect in humans involves broad corticospinal and spinal facilitation, accompanied by current direction-dependent modulation of cortical excitability measures. KEY POINTS SUMMARYO_LIVoluntary contraction in one limb can facilitate motor output in a distant limb, but the mechanisms underlying this remote interlimb facilitation remain unclear. C_LIO_LIWe tested whether remote lower-limb contraction modulates corticospinal output, intracortical excitability, and spinal motoneuron excitability in a resting hand muscle. C_LIO_LISingle-pulse transcranial magnetic stimulation showed that motor evoked potentials in the hand were facilitated during remote lower-limb contraction across multiple current directions, indicating a broad increase in net corticospinal output. C_LIO_LIPaired-pulse measures were modulated preferentially with anterior-posterior stimulation, with reduced short-interval intracortical inhibition and increased short-interval intracortical facilitation, suggesting current direction-dependent modulation of cortical excitability measures. C_LIO_LIF-wave amplitude and persistence were also enhanced during remote lower-limb contraction, indicating increased spinal motoneuron excitability. These findings provide converging evidence that the remote effect involves both cortical and spinal contributions. C_LI

K+ channels are important for controlling membrane potential and regulating functional properties of microglia. Whereas the inward-rectifying K+ (Kir) channel 2.1 modulates proliferation, voltage-gated K+ channels (Kv) are linked to inflammatory response in mouse microglia (mMG). These channels serve as possible drug targets but little is known regarding their activity in human microglia. We used patch-clamp recording to study membrane currents of primary human microglia (hMG) and human induced pluripotent stem cell-derived microglia-like cells (hiPSC-MGL) and compared them with mMG. Unlike mMG, hMG and hiPSC-MGL exhibited Kir2.1 currents only after LPS+IFN-{gamma} stimulation. Interestingly, Kv currents were not observed in hMG or hiPSC-MGL under any condition. While mMG had a progressively ameboid morphology after stimulation, hMG showed few morphological changes and hiPSC-MGL increased ramification. Overall, the activity of Kir2.1 and Kv channels in hMG and hiPSC-MGL differs fundamentally from mMG. Our findings highlight differences between species and underscore the need for translational approaches.

Multipotent mesenchymal stem cells (MSCs) including bone marrow stromal cells (BMSCs) have shown analgesic efficacy in recent years. Studies suggested that the therapeutic effect of MSCs was mediated by their secreted small extracellular vesicles (sEVs) mainly exosomes. The present study evaluated the antihyperalgesic effect of BMSC-related sEVs in a mouse model of neuropathic pain involving chronic constriction injury of the infraorbital nerve (CCI-ION). Our separation protocol generated EV particles mostly sized in the range of exosomes (30-170 nm) and express exosome marker proteins CD9, CD81, and Tsg101, suggesting their endosome origin. We show that intravenous injection of BMSC-related sEVs attenuated pain hypersensitivity induced by CCI-ION as indicated by decreased mechanical hypersensitivity (von Frey test) and reduced aversion to noxious stimulation (conditioned place avoidance test). The antihyperalgesic effect of sEVs was observed in both female and male animals, and the effect was dose-dependent. sEVs from NAIVE serum-treated BMSC cultures produced short-lasting antihyperalgesia in male but not female mice, suggesting a subtle sex difference. The antihyperalgesia of sEVs from BMSC culture was blocked by the pretreatment of the culture with GM4869, the antagonist of exosome secretion, suggesting that the effect was not related to other co-isolated soluble mediators but mediated by MSC-derived exosomes. Interestingly, the prior injury condition in which sEVs were isolated favors the pain-relieving effect of sEVs. sEVs isolated from the serum of BMSC-treated animals receiving tendon ligation (TL) injury attenuated hyperalgesia for 24 h, while sEVs from the serum of BMSC-treated NAIVE animals only attenuated hyperalgesia at 3 h after injection. sEVs from the BMSC culture treated with the serum of TL rats were antihyperalgesic, but sEVs from the BMSC culture treated with the serum of naive animals were ineffective. Our results indicate that BMSC-related sEVs produced antihyperalgesia similar to that produced by BMSCs. The results suggest that the interactions between BMSCs and injury conditions are crucially important for producing efficacious sEVs/exosomes and support that the effect of sEVs could be optimized by priming BMSCs with injury-related conditions.

Pleasurable urge to move to music is often referred to as groove. Although previous studies have shown an association between the supplementary motor area (SMA) and the groove experience, its causal role remains unclear. Here, we investigated whether the SMA is causally involved in groove experience during music listening using repetitive transcranial magnetic stimulation. Fifteen healthy participants completed three sessions on separate days: excitatory stimulation (intermittent theta burst stimulation; iTBS) over the SMA, inhibitory stimulation (continuous theta burst stimulation; cTBS) over the SMA, and sham stimulation (iTBS or cTBS) over the vertex. After each stimulation session, participants listened to five high-groove and five low-groove musical excerpts and rated urge-to-move and pleasure on a 0-100 scale. Heart rate was additionally recorded as an exploratory physiological measure during music listening. Linear mixed-effects models (LMM) showed that pleasure ratings, but not urge-to-move ratings, were higher following both iTBS and cTBS compared with sham stimulation. In exploratory LMMs, reduced log-transformed heart rate variability (HRV) significantly predicted higher pleasure ratings. These findings suggest that SMA stimulation modulates the pleasurable component of the groove experience, likely via network-level mechanisms rather than a simple linear relationship between SMA excitability and pleasure. They also raise the possibility that reduced parasympathetic activity, reflected by lower HRV, mediates the stimulation-related increase in musical pleasure. Future studies should investigate the causal roles of other brain regions as well as clarify the directionality between autonomic changes and the groove experience.

The amplitude of motor-evoked potentials (MEPs) elicited using transcranial magnetic stimulation (TMS) has been shown to decrease in the short interval prior to response initiation. The cause of this premovement MEP suppression is currently unclear and has been attributed to various processes such as preparation-related inhibition preventing the premature release of planned action or increasing signal-to-noise ratio to facilitate rapid response initiation. The present study explored whether the decrease in MEP amplitude is affected by the task requirements, using reaction time (RT) paradigms that differ in the timeline of preparation and initiation of a motor response. Participants completed simple RT (SRT), choice RT (CRT), and go/no-go (GNG) tasks, while TMS was applied at various times between the warning signal and go-signal. It was hypothesized that if MEP suppression relates to preparation level, the greatest suppression would be observed during the SRT and GNG tasks, as these paradigms encourage advance preparation and response inhibition. Conversely, if the reduction in corticospinal excitability is associated with facilitating response initiation processes, then suppression would be expected for all tasks, including the CRT paradigm in which preparation does not occur until presentation of the go-signal. Results showed MEP amplitudes decreased for all tasks as the go-signal approached; however, both the SRT and GNG had significantly greater MEP suppression 50 ms prior to, and coincident with the go-signal. These results indicate that the nature and origin of the suppression is likely multifactorial and relates to both preparatory and initiation-related processes, with the timeline and magnitude of suppression dependent on the nature of the task being executed. Impact StatementTranscranial magnetic stimulation was used to elicit motor-evoked potentials to examine the timeline of corticospinal activation during the instructed delay period for choice, simple and go/no-go reaction time tasks. For all tasks, corticospinal excitability was initially elevated compared to baseline, followed by a similar magnitude of early suppression. However, just prior to the go-signal, those tasks that allowed advance preparation showed additional suppression, providing novel information linking pre-movement corticospinal suppression to preparatory and inhibition processes.

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

Repetitive transcranial magnetic stimulation (rTMS) is used widely in neuroscience to study and alter neural plasticity. The cellular mechanisms underlying the effect of rTMS on the brain remain unclear but is primarily thought to act via activity-dependent synaptic plasticity mechanisms. Here we investigated whether chronic repetitive magnetic stimulation in vitro and in vivo can induce another form of activity-dependent neural plasticity, axon initial segment (AIS) plasticity. Cortical neurons isolated from postnatal wild-type mice were stimulated with 6 hours of sham, repetitive magnetic stimulation in the form of intermittent theta-burst stimulation (iTBS), or 15 mM potassium chloride, with changes to AIS location and length measured +0 hours and +24 hours post-stimulation. In addition, adult transgenic mice expressing green fluorescent protein at the AIS received daily sham or iTBS over the primary motor cortices for 7 consecutive days and processed for microscopy 3 hours after the last stimulation. Analysis of neurons stimulated in vitro showed that chronic iTBS caused bidirectional and time-dependent shifts to the AIS position relative to the soma and a delayed shortening of the AIS length at +24 hours. In the adult mice, 7 consecutive days of daily iTBS decreased AIS lengths in layers 2/3 and 5 pyramidal neurons. Our findings provide in vitro and in vivo evidence that rTMS induces neuronal plasticity outside of the synapse, which may contribute to the long-lasting effect of rTMS on the brain with repeated stimulation protocols.

Cervical spinal cord injury (SCI) frequently leads to life-threatening respiratory insufficiency by disrupting descending phrenic pathways. There is growing interest in non-invasive neuromodulatory approaches to enhance plasticity of spared respiratory circuits. We investigated whether cervical repetitive magnetic stimulation (rMS) applied to the injured cervical spinal cord promotes ventilatory recovery in a preclinical mouse model. Adult mice received a unilateral C3 hemicontusion followed by either rMS or sham stimulation. We found that rMS-treated mice significantly improved recovery of tidal volume and minute ventilation at 21 days post injury(dpi) compared to sham controls under various breathing conditions (isoflurane anesthesia, poikilocapnic phase and hypercapnic challenge). Correspondingly, diaphragm EMG enhanced ipsilateral hemidiaphragm activity in ventral and medial regions, and even contralateral hemidiaphragm activity in its ventral part. This was associated with a marked attenuation of the inflammatory response at the cervical spinal cord level. Indeed, rMS lowered astroglial, fibrotic scarring, pro-inflammatory CD68-, Iba1- microglial/macrophage markers. Moreover, perineuronal net expression (WFA positive staining) is globally reduced in the ventral spinal horn, whereas at the lesion site it is markedly increased and tightly wrapped around motoneurons. Together, these findings demonstrate that rMS promotes functional respiratory recovery after cervical SCI through combined enhancement of diaphragmatic motor output and modulation of the inflammatory and extracellular environment. Together, these functional and cellular findings indicate that spinal rMS promotes a permissive, pro-regenerative environment supporting respiratory circuit plasticity. We conclude that rMS significantly enhances ventilatory recovery via reduced inflammatory response and improved intraspinal rewiring after high cervical SCI, suggesting it is a promising non-invasive strategy. The ability of rMS to engage spared respiratory networks and support neuroplasticity highlights its promise as a safe, non-invasive therapeutic strategy with translational potential for rehabilitation of breathing function after SCI. One Sentence SummaryNoninvasive cervical magnetic stimulation improves breathing after spinal cord injury by boosting diaphragm activity and reducing inflammation.

Cerebrospinal fluid-contacting neurons (CSF-cNs) are mechanosensory cells in the spinal cord that detect compression and regulate locomotion, posture, and morphogenesis. Although CSF-cNs respond to changes in pH, neurotransmitters and metabolites, their chemosensory repertoire is not fully understood. Using hybridization chain reaction, we investigated the distribution of expression of chemoreceptors in CSF-cNs and neighboring cells in the spinal cord. We found that CSF-cNs express receptors for glutamate (grm2), somatostatin (sstr2) and low-density lipoprotein (LDL) (ldlrad2), indicating roles in detecting glutamate, somatostatin and LDL in the CSF. High LDL receptor expression in CSF-contacting cells suggests CSF lipid capture. Most receptors were enriched but not exclusive to CSF-cNs and also appeared in ependymal radial glial cells. Our findings indicate multiple chemosensory pathways can sustain long-distance communication between neurons and glia through the cerebrospinal fluid.

Pain captures attention and interferes with executive and motor processes but task performance may be preserved at the cost of more effort. In a preregistered fMRI study, 40 participants performed a visuomotor force-matching task at two force levels under individually calibrated painful or non-painful thermal stimulation, while reporting the intensity of perceived effort. Maintaining task performance under pain was associated with increased perceived effort and recruited brain regions involved in pain modulation and cognitive control. Region-of-interest analysis showed perceived effort was consistently linked to decreased anterior midcingulate cortex activity, whereas supplementary motor area contributions varied depending on its role in motor execution or pain processing. Across experimental condition, motor, pain-modulatory and cognitive-control regions were associated with effort perception. Independently of condition, effort perception was modulated by ventromedial prefrontal cortex and ventral striatum. These findings indicate that effort perception reflects brain activity within areas involved in motor, executive and valuation processes.

With few exceptions, pathological progression in ischemic stroke is presumed to occur uniformly within the ischemic core region. These exceptions include edema formation, brain tissue [Na+] increase, and the qualitative visually-observed decrease of brain tissue [K+], [K+]br, all of which occur in peripheral regions of the ischemic core. We hypothesize that [K+]br within these peripheral regions are heterogeneous (with lower [K+]br in the peripheral compared to the central ischemic core) and are not associated with neuronal degradation. Permanent focal ischemia in 13 rats was produced for 2.5-5 h. Brain sections were quantitatively stained for K+ to assess [K+]br variations between the peripheral and central ischemic core. Regions within the cortical ribbon were used to explore differing rates of K+-depletion expressed as the slopes of [K+]br vs. time relations. Adjacent sections were observed for reflective change and stained for microtubule-associated protein 2 (MAP2) to identify the ischemic region and to relate neuronal pathology to [K+]br variations. The mean value of normal cortex (NC) [K+]br was 96 mEq/kg and of K+-depletion in all ischemic regions over time was 12.2 mEq/kg/h, consistent with measurements from other studies. Exaggerated K+-depletion occurred in 56% of the peripheral ischemic core regions classed as depleted peripheral ischemic core (ICp-DP) regions. These were clearly separated (p<0.001) from the non-depleted peripheral ischemic core (ICp-ND) regions. The normal cortex (NC) regions show stability of [K+]br with a slope near zero. However, the 13.6 mEq/kg/h slopes of the central ischemic core (ICc) and ICp-ND regions were similar (p=0.99) and showed a significant decrease over time. The 6.2 mEq/kg/h slope of the ICp-DP regions was significantly different from that of the ICc (p=0.010) and the ICp-ND (p=0.0071). This lower slope of the ICp-DP curve 2.5 h after stroke onset is due to the accelerated K+-efflux from 0 to 2.5 h, as its value at stroke onset must be [~]100 mEq/kg. However, these differential K+ losses were not reflected in the homogeneous peripheral ischemic core MAP2 immunoreactivity losses. Unlike [K+]br, there was no difference between the MAP2 immunoreactivity in K+-depleted and non-K+-depleted peripheral ischemic core regions (ICp-ND vs ICp-DP, ICp-ND vs ICp-DP, unpaired t-test, p=0.83, p=0.16, respectively). While confirming previous results of quantitative regional losses of [K+]br in the ischemic core, we show that K+ dynamics within the peripheral and the central ischemic core are heterogeneous and not related to MAP2-assessed neuronal structural integrity: the K+-depleted regions in the peripheral ischemic core regions are presumably closer to glymphatic system and other K+-efflux pathways. Such differing K+ dynamics at the edge of the ischemic core in the hyper-acute period in first hours after ischemic onset possibly relate to the spreading depolarization-mediated expansion of the infarct during the period of secondary brain injury. Peripheral ischemic core regions with less K+ might limit spreading depolarization initiation and propagation if there is insufficient K+ for depolarization to occur and make restoration of parenchymal membrane potential improbable even if the functionality of the Na+,K+-ATPase is restored. Further study of differing K+-dynamics within the ischemic core might lead to a better understanding of ischemic stroke pathophysiology.

Mitochondrial calcium signaling integrates energy needs with energy production, amplifying or suppressing mitochondrial respiration in response to activity demand. Neuronal activity is tightly ATPcoupled to increases in mitochondrial calcium uptake, which stimulate the tricarboxylic acid cycle (TCA) and activate calcium-dependent enzymes important for ATP production via oxidative phosphorylation. The mitochondrial calcium uniporter (MCU) is the predominant source of matrix calcium and is differentially expressed across neuronal cell types, suggesting cell-type-specific differences in the coupling of activity-driven calcium levels and mitochondrial respiration. Here, we investigated whether elevating MCU expression enhances mitochondrial calcium uptake and oxidative phosphorylation in the hippocampus. We report that hippocampal mitochondria overexpressing MCU take up calcium at a faster rate without increased sensitivity to calcium overload. By modeling in vivo supply and demand, we found that hippocampal mitochondria overexpressing MCU are more efficient than control mitochondria at responding to increased bioenergetic demand. These findings reveal a role for MCU in modulating mitochondrial calcium uptake and boosting mitochondrial respiration under increasing demand, which contributes to our understanding of how specific cell types may adapt to different bioenergetic demands.

The availability of a pre-existing cognitive-motor schema accelerates the learning of novel motor information. The encoding of a novel schema-compatible, compared to-incompatible, motor sequence was recently shown to be supported by the left primary motor cortex (M1). However, causal evidence for the role of M1 in schema-mediated motor learning is currently lacking. In the current study, we aimed to address this knowledge gap by transiently disrupting M1 using inhibitory continuous theta burst stimulation (cTBS). Forty-eight young healthy participants learned a bimanual motor sequence task (cognitive-motor schema). Twenty-four hours later, they learned a novel sequence whose ordinal schematic structure was compatible with that learned on the previous day. To provide causal evidence for a role of M1 on such schema-mediated motor learning, we applied either cTBS or sham stimulation to the left M1 immediately prior to encoding the schema-compatible novel sequence. Electromyography results showed no evidence for an effect of left M1 cTBS on corticospinal excitability as measured with motor-evoked potentials. Similarly, behavioral results indicated no significant effect of cTBS on subsequent schema-mediated motor sequence learning. Altogether, the present data do not provide evidence for a causal role of the left M1 in schema-mediated motor sequence learning.