The cerebellum contributes to associative motor learning and sensorimotor coordination in part by tracking subsecond time intervals between behaviorally relevant events, raising the question of how duration, or absolute time, is encoded. Here, we investigated whether information about duration is present in Purkinje cell complex spikes during repetitive sensory stimuli. Crus I Purkinje cells expressing the fast calcium indicator GCaMP8f were imaged at high speed (250 fps), allowing detection of complex spike-associated calcium signals from hundreds of Purkinje cell dendrites simultaneously, with 4 ms temporal resolution, in awake head-fixed mice of both sexes. Air puffs were applied to the whisker pad in stimulus trains that varied in the mean and variance of interstimulus intervals (ISIs, 100-900 ms). In responsive cells, the mean probability of complex spike firing increased approximately fivefold ∼35 ms post-puff, primarily owing to well-timed spiking after the stimulus rather than an increase in spike rate. The maximal response probability, and in some cells also the response latency, varied linearly with ISI. The values of both variables were consistent for each ISI, regardless of the attributes of the stimulus train, suggesting that they carried information about absolute, rather than relative, durations between stimulus pairs. Because each puff evoked only one or zero complex spikes per Purkinje cell, the dependence of spike probability on ISI emerged as a trial-by-trial dependence of the degree of synchronous firing on ISI, suggesting that subsecond absolute timing of somatosensory signals may be represented by complex spike synchrony across populations of Purkinje cells.
Primary cilia are small organelles acting as cellular antennae that sense and transduce diverse signals, including developmental signaling pathways in the developing central nervous system (CNS). This signaling is essential for normal CNS development, as evidenced by the prevalence of neurodevelopmental phenotypes in conditions arising from primary cilia dysfunction (ciliopathies). Though significant research has focused on the roles of primary cilia during CNS development, the functions of primary cilia in the mature CNS have only recently become a focus of investigation. Primary cilia are present on most vertebrate cells, including mature neurons and astrocytes and reportedly localize G-protein-coupled receptors, voltage-gated ion channels, and even synaptic proteins. Moreover, recent evidence highlights the dense "contactome" of cilia in the brain with adjacent neuronal structures and has even identified axo-ciliary synapses. Primary cilia are therefore both perfectly equipped and positioned to participate in regulating mature neural circuits. Consistent with these observations, primary cilia have also been linked to neurological and psychiatric symptoms without underlying brain malformations, both in ciliopathies and in nonciliopathy neurological conditions like autism spectrum disorder and schizophrenia. In this review, we bridge insights from human disease to evidence gained from animal and cell models to highlight the evolving roles of primary cilia in the developing and mature CNS. Primary cilia in the developing brain act as classical cellular antennae sensing secreted ligands, while primary cilia in the mature brain may also be capable of contact-dependent signaling, indicating a potential shift in the signaling capacity of primary cilia in the CNS.
Phosphatidylinositol (4,5) bisphosphate (PI(4,5)P 2 ) plays important roles in development, signaling, intracellular trafficking and regulation throughout the nervous system. Using selective and combined gene ablation strategies, in mice of both sexes, we have determined the roles of this lipid and the kinase isoforms of the PIP5KI family primarily responsible for its synthesis in mouse retina. In rod cells, PI(4,5)P 2 localizes predominantly to the plasma membrane of inner and outer segments and is enriched in membranes near the synaptic termini. Disruption of the gene encoding the γ PIP5KI isoform, Pip5k1c , throughout the developing retina, using Cre expression driven by a Six3 transcription factor-dependent promoter, yields dramatic, but not complete, loss of the protein, with no apparent effects on morphology or function through the first 3-4 months after birth. Slowly progressing photoreceptor degeneration is observed at later ages. Complete loss of the γ isoform in rods, driven by the rhodopsin promoter-based iCre75 transgene, leads to no obvious developmental defects, but results in an earlier-onset rod degeneration. Germ-line ablation of neither the Pip5k1a nor the Pip5k1b gene leads to any observable morphological defects. Homozygous Pip5k1a ablation leads to functional defects in photoreceptors as revealed by reduced a-wave and b-wave amplitudes in the electroretinograms. On the background of rod-specific Pip5k1c ablation, Pip5k1a deficiency greatly accelerates retinal degeneration. These results reveal a complex interplay among PIP5KI isoforms in ensuring proper photoreceptor function and health, with apparent partial redundancy in fulfilling their critical functions. They underscore the important role of PI(4,5)P 2 in neuronal signaling and homeostasis. Significance Statement Phosphatidylinositol(4,5)P 2 , PI(4,5)P 2 , plays essential roles in nervous system development and function, but its roles in retina have been unknown. This study combines biochemistry, mouse genetics, light- and electron microscopy to reveal both specific and redundant functions for PIP 2 formed by different kinase isoforms in the mammalian retina. It has implications for retinal function, disease and therapy, and for the broader field of phosphoinositide regulation.
The amyloid precursor protein (APP), a key factor in Alzheimer's disease (AD) pathology, and its two mammalian homologs, amyloid precursor-like proteins 1 and 2 (APLP1 and APLP2), are considered as members of the synaptic adhesion molecule (SAM) family. They are localized to the pre- and postsynapse, form trans-cellular dimers, and have been shown to induce presynaptic differentiation in a heterologous synapse formation assay. We demonstrate that expression of all APP family members in non-neuronal cells also promotes dendritic excitatory postsynaptic differentiation in primary mouse neurons of either sex, similar to Neurexin1β and other SAMs. Synaptogenic activity was decreased by deletion of the E1 domain and increased upon inhibition of soluble APP (sAPP) generation, reinforcing that trans-cellular interaction of APP/APLPs can induce synaptogenesis. Consistent with this, the capacity of heterologously expressed APP to induce postsynaptic specializations in contacting dendrites was reduced by the absence of APP family members at the postsynaptic site and was lost in conditional triple knock-out (cTKO) neurons. Pharmacological analyses revealed that heterologous formation of pre- and postsynapses relies on proper microtubule and actin cytoskeleton dynamics, as well as the MAP kinase pathway, similar to what has been shown for Neurexin1β and Neuroligin1. However, inhibition of the PI3K/Akt pathway selectively impaired APP-induced postsynaptic differentiation, suggesting that distinct APP signaling pathways are required for pre- and postsynaptic differentiation. Collectively, our data highlight the role of all APP family members as SAMs in trans-synaptic signaling, providing key insights into their physiological function and advancing our understanding of AD-related synaptopathies.
Research on visually guided object manipulation has shown that participants fixate goal locations-including objects to be grasped and locations where they are placed-prior to hand arrival, with gaze serving two primary functions: directing the hand (or object in hand) to the vicinity of the goal using peripheral vision and gaze-related signals and guiding the hand using central vision as it approaches the goal. However, real-world manipulation tasks are often performed while concurrent monitoring of the environment, resulting in competition for gaze. We examined gaze-hand coordination under such conditions. Human participants of either sex performed a manipulation task that involved grasping balls and placing them at target locations, while concurrently monitoring a display to detect probabilistically occurring visual events, which required central vision. Participants managed gaze competition in two main ways. First, fixations allocated to the action task were brief and prioritized directing the hand toward the goal (object or target location); participants then relied on tactile feedback to complete the action (grasping or placing the object). When tactile feedback was reduced-by using a tool instead of the fingertips to perform the task-gaze additionally served the guiding function. Second, participants reduced gaze competition by exploiting temporal regularities of events in the monitoring task. Specifically, they adjusted both gaze allocation and hand movement timing to reduce the likelihood that action task fixations would coincide with visual events. These findings demonstrate how individuals flexibly integrate sensorimotor control with analysis of environmental statistics to manage competing visual demands.
Reproductive function in female mammals is largely orchestrated by the hypothalamic-pituitary-gonadal axis, which generates rhythmic hormonal fluctuations underlying the estrous cycle. Part of this cycle, the preovulatory LH surge, is tightly gated by the circadian system. The suprachiasmatic nucleus (SCN)-the central circadian clock-plays a critical role in this temporal regulation and among SCN-derived signals, neuropeptides such as arginine vasopressin (AVP), and vasoactive intestinal peptide (VIP) have been proposed to mediate this process. Notably, most SCN neurons are GABAergic; however, the contribution of SCN-derived GABAergic transmission in the female reproductive system remains unclear. To investigate the role of GABAergic output from the SCN, we first performed AAV-mediated SCN ablation in Vgat-IRES-Cre mice (Vgat; encoding the vesicular GABA transporter), resulting in disrupted estrous cycles. To assess GABAergic transmission from specific SCN populations, we next examined Avp-Vgat-/- and Vip-Vgat-/- mice, in which the Vgat gene is selectively deleted in AVP or VIP neurons. Vip-Vgat-/- females showed regular cycles. However, Avp-Vgat-/- females exhibited marked disruptions, and AAV-mediated Vgat rescue in AVP neurons in the SCN (SCN-AVP) restored normal estrous cycles. Anterograde tracing revealed dense SCN-AVP terminals in the anteroventral periventricular nucleus (AVPV), which contains kisspeptin neurons, but few projections to other major reproductive neuroendocrine populations. These findings suggest GABAergic output from SCN-AVP neurons stabilizes the estrous cycle, potentially via kisspeptin neurons in the AVPV, thereby highlighting that GABAergic signaling also contributes to female reproductive regulation alongside AVP and VIP.
SLC6A8 encodes the creatine transporter (CRT), which mediates creatine transport across the plasma membrane in the brain, including the blood-brain barrier and neurons. Creatine transporter deficiency (CTD), caused by pathogenic variants in SLC6A8, leads to cerebral creatine depletion and cognitive impairment. Here, we investigated the developmental molecular mechanisms underlying CTD using the pathogenic c.1681G>C (G561R) variant of Slc6a8, which corresponds to a variant identified in SLC6A8 in a patient with CTD. In vitro analyses using HEK293 cells expressing mutant mouse CRT carrying the G561R variant demonstrated impaired N-glycan maturation and plasma membrane localization of the transporter, resulting in markedly reduced creatine uptake, consistent with previous reports on the corresponding human CRT variant. To investigate the in vivo effects of this pathogenic variant, we generated CRT-G561R knock-in mice by introducing the c.1681G>C point mutation into the mouse Slc6a8 gene using the CRISPR/Cas9 system. These male mice exhibited severe reductions in brain creatine levels, postnatal growth retardation, and impaired spatial memory, despite preserved gross brain morphology. Quantitative proteomic analyses of the hippocampus and cerebral cortex during postnatal development revealed region-dependent protein alterations in CTD. The hippocampus showed pronounced early postnatal remodeling involving proteins related to actin cytoskeleton organization and vesicle-mediated membrane trafficking, whereas the cerebral cortex exhibited a more gradual response involving creatine biosynthesis-related enzymes and later-emerging mitochondrial pathways, including the mitochondrial translation machinery. These findings demonstrate stage- and region-dependent proteomic remodeling during postnatal brain development in CTD.
Two prominent accounts describe the functional organization of human high-level visual cortex. A categorical view emphasizes category-selective areas, while a dimensional view highlights continuous feature maps spanning these areas. Here, we asked whether these two views reflect complementary expressions of the same underlying organization. Using a data-driven decomposition of fMRI responses from human participants (female and male) in face-, body-, and scene-selective areas, we identified spatially overlapping activity patterns that were shared across individuals. Each area encoded multiple interpretable dimensions capturing both finer within-category and coarser between-category distinctions, even in the most category-selective voxels. These dimensions formed distinct clusters within category-selective areas but extended as distributed maps across visual cortex. Together, these findings reveal an underlying organization that links category-selective areas to continuous feature maps, thereby reconciling categorical and dimensional accounts of high-level visual cortex.
Trauma to the spinal cord initiates an inflammatory response causing secondary damage, which collectively can result in loss of function below the level of the injury. The unbalanced risk-benefit ratio of methylprednisolone led to development of therapeutic nanoparticles (NPs) that associate with circulating monocytes and neutrophils to reduce inflammation and secondary damage and improve functional recovery in a female mouse model of cervical hemisection spinal cord injury. Herein, we investigate the mechanisms occurring during the acute phase of injury by which NPs directly and indirectly modulate the phenotype and trafficking of monocytes and neutrophils and computationally catalog the communication network among cell types within the injury microenvironment. Using adoptive transfer to monitor trafficking, NP treatment reduced the extent of myeloid cell recruitment to the injury yet did not impact the composition of adoptively transferred monocytes or neutrophils. The proportion of inflammatory monocytes was reduced with NP treatment, and single-cell sequencing analysis indicated increased polarization toward pro-regenerative phenotypes. Sequencing analysis also demonstrated that outgoing signals from monocytes and neutrophils influenced the phenotype of numerous cell types, including endothelial cells, fibroblasts, oligodendrocyte progenitor cells, and Schwann cells. Signaling between cell compartments involves a combination of soluble and matrix signals, with NP treatment enhancing expression of genes associated with anti-inflammatory phenotypes, angiogenesis, neuroprotection, and promotion of axon outgrowth or decreasing expression of inhibitors to regeneration. Collectively, NP delivery leads to direct and indirect effects on monocytes and neutrophils, which subsequently influence gene expression and intercellular signaling networks that promote a pro-regenerative environment.
This Viewpoint argues that understanding how the brain controls behavior requires an explicitly evolutionary framework. The mammalian brain did not emerge through the replacement of earlier circuits with perfect alternatives but rather through the elaboration of existing circuits along with the addition of new ones, yielding a hierarchical architecture in which many ancient spinal and brainstem circuits remain functionally essential. In this context, cortex does not directly control behavior but exerts its influence via layer 5 projections to evolutionarily older subcortical motor centers. This view challenges the prevailing corticocentric bias in neuroscience, which often treats cortex as a largely self-contained computational system. We propose that key functions such as attention and efference copy are best understood within this layered organization. Attention may reflect competitive filtering of corticofugal outputs at subcortical bottlenecks, while efference copies arise naturally from branching motor pathways distributed across hierarchical levels that reflect evolutionary history. Crucially, these principles expose important limitations in current computational models, which typically omit subcortical circuitry and treat motor output as a terminal stage of processing. An evolutionary perspective instead demands models that integrate cortex with spinal, brainstem, and midbrain systems as interacting components of a unified sensorimotor hierarchy. Incorporating these constraints will be essential for developing biologically grounded theories of brain function.
Human immunodeficiency virus 1 (HIV-1) infection often results in sensory neuropathy, with >60% of affected individuals developing chronic pain. Although viral proteins such as glycoprotein 120 (gp120) contribute to neuronal injury and pain hypersensitivity, their specific effects on nociceptive signaling remain unclear. Hyperactivity of N-methyl-d-aspartate receptor (NMDAR) in the spinal dorsal horn is a hallmark of neuropathic pain. Here, we determined how gp120 affects synaptic NMDAR activity in spinal excitatory and inhibitory neurons in male and female mice. Intrathecal gp120 enhanced expression of α2δ-1 and GluN1 in the dorsal root ganglion (DRG) and spinal cord. Gp120 also increased α2δ-1-GluN1 interaction and their synaptic trafficking in the spinal cord. Functionally, gp120 induced hyperactivity of presynaptic NMDARs on primary afferent terminals and postsynaptic NMDARs in vesicular glutamate transporter 2-expressing excitatory, but not vesicular GABA/glycine transporter-expressing inhibitory, dorsal horn neurons. Importantly, gp120-induced hyperactivity of both presynaptic and postsynaptic NMDARs was eliminated by the α2δ-1 inhibitory ligand gabapentin or by an α2δ-1 C-terminal peptide that disrupts α2δ-1-NMDAR interactions. Correspondingly, treatment with the NMDAR antagonist, gabapentin, or α2δ-1 C-terminal peptide consistently reversed gp120-induced persistent nociceptive hypersensitivity. Furthermore, genetic deletion of Cacna2d1 or selective ablation of GluN1 in DRG neurons significantly attenuated gp120-induced nociceptive hypersensitivity. Together, these findings indicate that gp120 drives nociceptive hypersensitivity by augmenting presynaptic and postsynaptic activity of α2δ-1-bound NMDARs, thereby amplifying nociceptive transmission from primary afferents to spinal excitatory neurons. Targeting α2δ-1-associated NMDARs may therefore represent a promising therapeutic approach for HIV-associated chronic neuropathic pain.
Unlike any other organ, the brain's role in identity, agency, and experience makes it biologically and culturally unique. The transformative potential of global neuroscience demands robust, integrated ethical engagement across the research life cycle. Neuroscientists and neuroengineers need to be equipped with a neuroethics familiarity that transcends the compliance training of older generations. Neuroethics must be an integral part of their work. This paper advocates for a proactive "neuroethics-by-design" (NxbD) approach. NxbD offers a reflective lens as well as an operational methodology that can iteratively shape hypotheses, experiments, technological architectures, and translation of the work to wider society. While NxbD is conceived as a toolkit for researchers, the responsibility of considering and addressing these issues is not theirs alone. NxbD is most effectively conceptualized as a shared responsibility that is evaluated and enacted by multiple communities. Such an approach is an investment in our collective future in which we can all contribute.
The reversal of learning-induced synaptic potentiation through depotentiation may be important in certain types of forgetting. Here, we evaluated how synaptic plasticity induced by different stimuli in the hippocampus is affected by mechanistically distinct forms of depotentiation. In hippocampal slices obtained from male and female mice, we artificially induced long-term potentiation (LTP) using either a temporally spaced or compressed stimulation pattern. Using a combination of electrophysiology and protein quantification approaches, we found divergent molecular pathways recruited during depotentiation of spaced and compressed LTP. Depotentiation of both forms of LTP required glutamatergic activation of the N-methyl-d-aspartate receptor (NMDAR). However, depotentiation of compressed, but not spaced, LTP shared a requirement with long-term depression for intracellular non-ionotropic NMDAR (NI-NMDAR) signaling cascades mediated by the C-terminal domain of GluN1. Downstream of NMDAR signaling, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor phosphorylation was also differentially modified during depotentiation of spaced and compressed LTP. Finally, we found that depotentiation of spaced but not compressed LTP required synaptic Arc. Altogether, we identify the role of NI-NMDAR signaling in synaptic depotentiation. Additionally, we reveal two mechanistically distinct forms of NMDAR-dependent depotentiation that can be selectively induced after different temporal patterns of LTP induction. Our findings have important implications for the regulation of physiological and pathological forgetting.
Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising noninvasive neuromodulation technique with growing therapeutic relevance. Although increasingly combined with physical therapy in neurorehabilitation, its mechanistic effects during active movement remain poorly understood, as most physiology studies examine taVNS at rest, overlooking the dynamic neural activity engaged during movement. This study aimed to determine the neurophysiological basis for pairing taVNS bursts with movement. Thirty-six healthy adults (10 females, 26 males) completed two experiments where 2 s taVNS bursts were delivered. The first experiment assessed autonomic [heart rate (HR), galvanic skin response (GSR)], neuromodulatory (pupil diameter), and cortical [electroencephalography (EEG) spectral slope] responses during a randomized trial design involving three stimulation conditions (taVNS, earlobe sham, no stimulation) and two behavioral contexts [movement (go) vs still (no-go)]. The second experiment evaluated corticospinal excitability by measuring transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEPs) during taVNS. taVNS increased TMS-induced MEP amplitudes, indicating transient facilitation of corticospinal output when stimulation coincides with an engaged motor system. Concordantly, EEG sensorimotor activity was enhanced by taVNS during movement but not during stillness. In contrast, pupil diameter showed a clear phasic response to stimulation in both movement and still conditions, consistent with state-independent neuromodulatory engagement. Autonomic indices were not additionally modulated by phasic taVNS beyond movement-related changes. These findings identify a state-dependent window in which taVNS preferentially boosts task-engaged motor circuitry rather than producing nonspecific autonomic activation, providing mechanistic support for movement-paired stimulation protocols and highlighting pupil, EEG, and MEPs as sensitive biomarkers of phasic taVNS effects.
Protein tyrosine phosphatase δ (PTPδ) is involved in Sema3A-induced dendritic elaboration of cortical pyramidal neurons through the activation of Fyn tyrosine kinase. However, the in vivo substrates of PTPδ remain largely unknown. Phosphotyrosine proteome analysis of Ptpδ -/- mice brains from both male and female revealed that signal regulatory protein α (SIRPα) was hyperphosphorylated at the carboxy-terminal Tyr501 residue in the knock-outs. Immunohistochemistry with anti-phospho-Tyr501 SIRPα antibody showed the hyperphosphorylation of SIRPα in various regions including the olfactory nerve layer, cortex, striatum, thalamic reticular, and hypothalamic nuclei in Ptpδ-/- brain sections. These regions partially correlated with PTPδ expression. In the primary cultured wild-type (wt) mouse dorsal root ganglion neurons, Sirpα knockdown or overexpression of a cytoplasmic deleted SIRPα mutant partially blocked the Sema3A-induced growth cone collapse response. However, overexpression of nonphosphorylated mutants of SIRPα did not alter the response. This suggests that SIRPα is involved in the Sema3A-induced collapse response in an independent manner of phosphorylation and/or dephosphorylation. In the primary cultured cortical neurons, Sirpα knockdown or the overexpression of SIRPα-Tyr501Phe mutant attenuated Sema3A-induced dendritic growth. In cultured Sirpα -/- cortical neurons, re-expression of wt SIRPα, but not of SIRPα-Tyr501Phe, restored Sema3A-induced dendritic formation. In vivo analyses revealed ectopic expression of SIRPα-Tyr501Phe in cortical layer II/III pyramidal neurons with misoriented apical dendrites and attenuated basal dendrite arborization. Similar irregular cortical dendrites were observed in Sirpα -/- and Ptpδ -/- brains. Collectively, our results demonstrate that PTPδ regulates the dendritic elaboration of cortical pyramidal neurons through the dephosphorylation of SIRPα.
