bioRxiv Subject Collection: Neuroscience's Journal

Optimal sigmoid function models for analysis of transspinal evoked potential recruitment curves recorded from different muscles
Recruitment input-output curves of transspinal evoked potentials that represent the net spinal motor output of alpha motor neurons, and those of cortically, spinally or peripherally induced responses are used extensively in research as neurophysiological biomarkers to establish physiological or pathological behavior of neuronal networks as well as post-treatment recovery. A comparison between different sigmoidal models to fit the transspinal evoked potentials recruitment curve and estimate the parameters of physiological importance has not been performed. This study sought to address this gap by fitting eight sigmoidal models (Boltzmann, Hill, Log-Logistic, Log-Normal, Weibull-1, Weibull-2, Gompertz, Extreme Value Function) to the transspinal evoked potentials recruitment curves of soleus and tibialis anterior recorded under four different cathodal stimulation settings. The sigmoidal models were ranked based on the Akaike information criterion, and their performance was assessed in terms of Akaike differences and weights values. Additionally, an interclass correlation coefficient between the predicted parameters derived from the best models fitted to the recruitment curves was also established. A Bland-Altman analysis was conducted to evaluate the agreement between the predicted parameters from the best models. The findings revealed a muscle dependency, with the Boltzmann and Hill models identified as the best fits for the soleus, while the Extreme Value Function and Boltzmann models were optimal for the tibialis anterior transspinal evoked potentials recruitment curves. Excellent agreement for the upper asymptote, slope, and inflection point parameters was found between Boltzmann and Hill models for the soleus, and for slope and inflection point parameters between Extreme Value Function and Boltzmann models for the tibialis anterior. Notably, the Boltzmann model for soleus and the Extreme Value Function model for tibialis anterior exhibited less susceptibility to inaccuracies in estimated parameters. Based on these findings, we suggest the Boltzmann and the Extreme Value Function models for fitting the soleus and the tibialis anterior transspinal evoked potentials recruitment curve, respectively.

Oxytocin facilitates social behavior of female rats via selective modulation of interneurons in the medial prefrontal cortex
The hypothalamic neuropeptide oxytocin is best known for its prosocial behavioral effects. However, the precise anatomical and cellular targets for oxytocin in the cortex during social behavior remain elusive. Here we show that oxytocin neurons project directly to the medial prefrontal cortex where evoked axonal oxytocin release facilitates social behaviors in adult female rats. In conjunction, we report that local oxytocin receptor (OTR+) expressing cells are predominantly interneurons whose activation promotes social interaction. In particular, in a state of food deprivation, this inhibitory neuronal subpopulation shifts the preference from appetitive food stimuli towards a social stimulus. We further demonstrate that activation of these OTR+ interneurons inhibits principal cells specifically projecting to the basolateral amygdala, thus providing a putative mechanism of selective oxytocin action in this sociability promoting cortical network.

Excitability modulations of somatosensory perception do not depend on feedforward neuronal population spikes
Neural states shape perception at earliest cortical processing levels. Previously we showed a relationship between the N20 component of the somatosensory evoked potential (SEP), pre-stimulus alpha oscillations, and the perceived intensity in a somatosensory discrimination paradigm (Stephani et al., 2021, eLife). Here we address the follow-up question whether these excitability dynamics reflect changes in feedforward or feedback signals. Re-examining the previous EEG data, we leveraged high-frequency oscillations (HFO) as a metric for neuronal population spiking activity of the first excitatory feedforward volley in the cortex. Using Bayesian statistics, we found evidence against the involvement of HFO in moment-to-moment variability of perceived stimulus intensity, in contrast to previously observed pre-stimulus alpha and N20 effects. Given that the N20 component presumably reflects backpropagating membrane potentials towards the apical dendrites, we argue that top-down feedback processes (e.g., related to alpha oscillations) may thus rely on modulations at distal sites of involved pyramidal cells rather than on output firing changes at basal compartments.

Unaware Processing of Words Activates Experience-Derived Information in Conceptual-Semantic Brain Networks
The recognition of manipulable objects results from the encoding of sensory input in combination with predictive decoding of experience-derived visuomotor information stored in conceptual-semantic representations. This grounded interpretive processing was previously found to subsist even under unaware perception of manipulable object pictures. In this fMRI study, we first aimed to extend this finding by testing whether experientially grounded visuomotor representations are unawarely recruited when manipulable objects are not visually depicted, but only referred to by words presented subliminally through continuous flash suppression. Second, we assessed the generalizability of decoding experience-derived conceptual information to other semantic categories, by extending our investigation to subliminally presented emotion words and testing for unaware recruitment of grounded emotion representations in the limbic system. Univariate analysis of data sampled from 21 human participants (14 females) showed that manipulable object words selectively activated a left-lateralized visuomotor network, both when words were presented below perceptual threshold and when participants subjectively reported lack of stimulus awareness. Emotion words selectively engaged the bilateral limbic network, although univariate analysis did not provide evidence for its recruitment under subliminal perceptual conditions. In turn, multivariate pattern analysis showed that neural codes associated with both manipulable object and emotion words could be decoded even in the absence of perceptual awareness. These findings suggest that the brain automatically engages in conceptual-semantic decoding of experience-derived information not only when circumstances require to interact with manipulable objects and emotions, but also when these referents are dislocated in time and space and only referred to by words.

A peptide-neurotensin conjugate that crosses the blood-brain barrier induces pharmacological hypothermia associated with anticonvulsant, neuroprotective and anti-inflammatory properties following status epilepticus in mice
Preclinical and clinical studies show that mild to moderate hypothermia is neuroprotective in sudden cardiac arrest, ischemic stroke, perinatal hypoxia/ischemia, traumatic brain injury and seizures. Induction of hypothermia largely involves physical cooling therapies, which induce several clinical complications, while some molecules have shown to be efficient in pharmacologically-induced hypothermia (PIH). Neurotensin (NT), a 13 amino-acid neuropeptide that regulates body temperature, interacts with various receptors to mediate its peripheral and central effects. NT induces PIH when administered intracerebrally. However, these effects are not observed if NT is administered peripherally, due to its rapid degradation and poor passage of the blood brain barrier (BBB). We conjugated NT to peptides that bind the low-density lipoprotein receptor (LDLR) to generate vectorized forms of NT with enhanced BBB permeability. We evaluated their effects in epileptic conditions following peripheral administration. One of these conjugates, VH-N412, displayed improved stability, binding potential to both the LDLR and NTSR-1, rodent/human cross-reactivity and improved brain distribution. In a mouse model of kainate (KA)-induced status epilepticus (SE), VH-N412 elicited rapid hypothermia associated with anticonvulsant effects, potent neuroprotection and reduced hippocampal inflammation. VH-N412 also reduced sprouting of the dentate gyrus mossy fibers and preserved learning and memory skills in the treated mice. In cultured hippocampal neurons, VH-N412 displayed temperature-independent neuroprotective properties. To the best of our knowledge, this is the first report describing the successful treatment of SE with PIH. In all, our results show that vectorized NT may elicit different neuroprotection mechanisms mediated either by hypothermia and/or by intrinsic neuroprotective properties.

Canonical time-series features for characterizing biologically informative dynamical patterns in fMRI
The interdisciplinary time-series analysis literature encompasses thousands of statistical features for quantifying interpretable properties of dynamical data. But for any given application, it is likely that just a small subset of informative time-series features is required to capture the dynamical quantities of interest. So, while comprehensive libraries of time-series features have been developed, it is useful to construct reduced and computationally efficient subsets for specific applications. In this work, we demonstrate a systematic process to deduce such a reduced set, focused on the problem of distinguishing changes to functional Magnetic Resonance Imaging (fMRI) time series caused by a range of experimental manipulations of excitatory and inhibitory neural activity in mouse cortical circuits. We reduce a comprehensive library of over 7000 candidate time-series features down to a subset of 16 features, which we call catchaMouse16, that aims to both: (i) accurately characterize biologically relevant properties of fMRI time series; and (ii) minimize inter-feature redundancy. The catchaMouse16 feature set accurately classifies experimental perturbations of neuronal activity from fMRI recordings, and also shows strong generalization performance on an unseen mouse and human resting-state fMRI data where it tracks spatial variations in excitatory and inhibitory cortical cell densities, often with greater statistical power than the full hctsa feature set. We provide an efficient, open-source implementation of the catchaMouse16 feature set in C (achieving an approximately 60 times speed-up relative to the native Matlab code of the same features), with wrappers for Python and Matlab. This work demonstrates a procedure to reduce a large candidate time-series feature set down to the key statistical properties of mouse fMRI dynamics that can be used to efficiently quantify and interpret informative dynamical patterns in neural time series.

Enhancing sleep via rocking ameliorates motor behavior and reduces beta-amyloid levels in a mouse model of Alzheimer's disease
Alzheimer's disease (AD) is a progressive neurodegenerative disorder associated with cognitive decline and characterized by beta-amyloid plaque and tau tangle pathology. Recent research indicates a bidirectional relationship between AD pathology and sleep disturbances, with disrupted sleep exacerbating AD progression through increased beta-amyloid and tau accumulation. This strongly indicates that improving sleep may exert a direct protective effect on preventing the accumulation and spreading of AD pathology, and possibly slow the cognitive decline. Here we investigated the effects of enhancing sleep via vestibular stimulation (rocking) on AD progression in a 3xTg mouse model. Over a four-month period starting in early adulthood (p60), we monitored sleep patterns, motor function, memory, and AD pathology. Twelve-hour rocking during the light period significantly increased non-rapid eye movement (NREM) sleep duration in mice, although this effect diminished over time due to habituation. Despite this, rocking attenuated motor function decline and reduced beta-amyloid levels in the cerebral cortex of treated mice. No noticeable changes in tau levels were observed following sleep enhancement. In conclusion, our findings highlight the potential of non-pharmacological methods to enhance NREM sleep and modify disease trajectory in AD models, emphasizing the critical role of sleep in neuroprotection.

Large-scale Dynamical Fingerprints of Distributed Synaptic Alterations in Early-Stage Psychosis
Psychotic disorders, such as schizophrenia, present a major challenge for research and clinical practice: its pathogenesis is complex and only partially understood, the individual symptomatology is heterogenous, and there is a lack of biomarkers for the early detection, diagnosis, and individualized treatment. The underlying synaptic and microcircuitry alterations are widely distributed across the cerebral cortex. Here, we developed a magnetoencephalography approach to map the resulting cortex-wide alterations of local cortical population dynamics. We identified large-scale patterns of changes in cortical dynamics that were remarkably similar between first-episode psychosis patients and individuals at clinical high risk for psychosis. These spatial patterns also resembled those induced by pharmacological manipulations of excitatory NMDA glutamate receptors and inhibitory GABA-A receptors in healthy participants. Differences in those spatial patterns of cortical dynamics between first-episode psychosis patients related to individual symptomatology. Our approach and results open a window on the distributed pathophysiology of psychosis.

Insights into the foraging Gene's Influence on Mating Investments of Male Drosophila
The foraging gene is a key genetic factor that modulates social behavior in insects, primarily by governing the trade-off between individual foraging and group-related activities. It has been associated with various behaviors associated with food search and resource exploitation, thereby playing a crucial role in determining the efficiency of foraging and the overall success of the collective. In this study, we investigate the critical role of the foraging gene in mediating complex interval timing behaviors, particularly mating duration, in the fruit fly Drosophila melanogaster. By examining two distinct variant phenotypes, rover and sitter, we observe specific deficiencies in longer (LMD) and shorter mating duration (SMD) behaviors, respectively, suggesting the genes crucial influence on these interval timing mechanisms. Utilizing single-cell RNA sequencing and knockdown experiments, we identify the genes significant expression in key neurons involved in learning and memory. However, its impact on mating duration is not observed in these brain regions. Instead, our data reveal the genes crucial role in specific neurons expressing Pdfr, a critical regulator of circadian rhythms. Furthermore, the study uncovers sexually dimorphic expression patterns in the brain and highlights the necessity of the genes dosage in specific cell populations within the ellipsoid body for normal mating duration. These findings underscore the foraging genes pivotal role in mediating complex interval timing behaviors in Drosophila, providing valuable insights into the intricate interplay between genetics, environment, and behavior. This research contributes to a deeper understanding of the genetic and neural mechanisms underlying complex interval timing behaviors, with broader implications for unraveling the function of foraging gene.

Criticality explains structure-function relationships in the human brain
Healthy brain exhibits a rich dynamical repertoire, with flexible spatiotemporal patterns replays on both microscopic and macroscopic scales. How do fixed structural connections yield a diverse range of dynamic patterns in spontaneous brain activity? We hypothesize that the observed relationship between empirical structure and functional patterns is best explained when the microscopic neuronal dynamics is close to a critical regime. Using a modular Spiking Neuronal Network model based on empirical connectomes, we posit that multiple stored functional patterns can transiently reoccur when the system operates near a critical regime, generating realistic brain dynamics and structural-functional relationships. The connections in the model are chosen as to force the network to learn and propagate suited modular spatiotemporal patterns. To test our hypothesis, we employ magnetoencephalography and tractography data from five healthy individuals. We show that the critical regime of the model is able to generate realistic features, and demonstrate the relevance of near-critical regimes for physiological brain activity.

Complementary Organization of Driver and Modulator Cortico-Thalamo-Cortical Circuits
Corticocortical (CC) projections in the visual system facilitate the hierarchical processing of sensory information. In addition to direct CC connections, indirect cortico-thalamo-cortical (CTC) pathways through the pulvinar nucleus of the thalamus can relay sensory signals and mediate interactions between areas according to behavioral demands. While the pulvinar is extensively connected to the entire visual cortex, it is unknown whether transthalamic pathways link all cortical areas or whether they follow systematic organizational rules. Because pulvinar neurons projecting to different cortical areas are spatially intermingled, their input/output relationships have been difficult to characterize using traditional anatomical methods. To determine the organization of CTC circuits, we mapped the higher visual areas (HVAs) of mice with intrinsic signal imaging and targeted five pulvinar[->]HVA pathways for projection-specific rabies tracing. We aligned post-mortem cortical tissue to in vivo maps for precise quantification of the areas and cell types projecting to each pulvinar[->]HVA population. Layer 5 corticothalamic (L5CT) ''driver'' inputs to the pulvinar originate predominantly from primary visual cortex (V1), consistent with the CC hierarchy. L5CT inputs from lateral HVAs specifically avoid driving reciprocal connections, consistent with the ''no-strong-loops'' hypothesis. Conversely, layer 6 corticothalamic (L6CT) ''modulator'' inputs are distributed across areas and are biased toward reciprocal connections. Unlike previous studies in primates, we find that every HVA receives disynaptic input from the superior colliculus. CTC circuits in the pulvinar thus depend on both target HVA and input cell type, such that driving and modulating higher-order pathways follow complementary connection rules similar to those governing first-order CT circuits.

Neurophysiological correlates of cortical hierarchy across the lifespan
The brain processes information along a hierarchical structure, forming a gradient of cortical hierarchy from sensorimotor areas to transmodal areas. Here, we aim to understand which aspects of neural dynamics characterize this gradient and whether the respective spatial distribution varies across the lifespan. Therefore, we extracted neurophysiological features from magnetoencephalography recordings in 350 participants between 18 and 88 years during rest. Among traditional features related to the power spectrum, delta power (1-4 Hz) showed the most robust association with cortical hierarchy, increasing along this axis. Beyond traditional features, we employed comprehensive time-series characterization and identified a novel hierarchy-sensitive feature capturing the variability of the signals mean over time. This feature increases along the cortical hierarchy, suggesting that higher-level brain areas exhibit more dynamic and context-dependent activity patterns. Furthermore, we highlight changes in the gradient of brain dynamics across the lifespan. Alpha power distribution, for instance, exhibits a posterior-anterior gradient in young adults that becomes less pronounced with increasing age. Further, the change of the autocorrelation and auto mutual information function along the cortical hierarchy is heavily modulated by age. These findings reveal simple but robust neurophysiological markers of cortical hierarchy and highlight the dynamic nature of the brains organization throughout life.

A focal traumatic injury to the spinal cord causes an immediate and massive spreading depolarization sustained by chloride ions, with transient network dysfunction and remote cortical glia changes.
In clinics, physical injuries to the spinal cord cause a temporary motor areflexia below lesion, known as spinal shock. This topic is still underexplored due to the lack of preclinical SCI models that do not use anesthesia, which would affect spinal excitability. Our innovative design considered a custom-made micro impactor that provides localized and calibrated strikes to the ventral surface of the thoracic spinal cord of the entire CNS isolated from neonatal rats. Before and after injury, multiple ventral root (VR) recordings continuously traced respiratory rhythm, baseline spontaneous activities, and electrically-induced reflex responses. As early as 200 ms after impact, an immediate transient depolarization spread from the injury site to the whole spinal cord with distinct segmental velocities. Stronger strikes induced higher potentials causing, at the site of injury, a transient drop in tissue oxygen levels and a massive cell death with complete disconnection of longitudinal tracts. Below the impact site, expiratory rhythm and spontaneous lumbar activity were suppressed. On lumbar VRs, reflex responses transiently halted but later recovered to control values, while electrically-induced fictive locomotion remained perturbed. Moreover, low-ion modified Krebs solutions differently influenced impact-induced depolarizations, the magnitude of which amplified in low-Cl-. Moreover, remote changes in cortical glia occurred soon after spinal damage. Overall, our novel in vitro platform traces the immediate functional consequences of impacts to the spinal cord during development. This basic study provides insights on the SCI pathophysiology, unveiling an immediate chloride dysregulation and transient remote glial changes in the cortex.

Grape extract and resveratrol mitigate sleep fragmentation, Aβ accumulation, and abnormal neuronal excitability in a Drosophila model of Alzheimer's disease
Consumption of red wine and grape extracts may offer a range of health benefits, largely attributable to the grapes rich content of vitamins, fiber, and antioxidant compounds, such as polyphenols. To determine if resveratrol (RES) present in grape extracts is responsible for these benefits, we conducted a study on the effects of red grape skin extract (GSKE), seed extract (GSEE), and RES on sleep patterns, amyloid-beta (A{beta}) deposition, neuronal excitability, and lifespan in a Drosophila model expressing A{beta}42. A{beta}42 flies experienced significant sleep fragmentation at night, yet their overall sleep duration was unaffected. Dietary GSKE significantly enhanced sleep duration and mitigated sleep fragmentation in these flies, whereas GSEE only increased the duration of sleep bouts during the day. RES demonstrated a similar effect, albeit to a lesser extent compared to GSKE. All three dietary interventions led to a reduction in A{beta}42 levels and an extension of the lifespan in A{beta}42 flies, with GSEE showing the least pronounced effects. Furthermore, GSEE and RES were able to reverse the hyperexcitability of mushroom body neurons (MBNs) caused by A{beta}42 expression. These results suggest that GSKE and RES are potent promoters of sleep and have the potential to ameliorate sleep disturbances. Additionally, the study highlights that other bioactive component in GSKE, beyond RES, may contribute to its diverse pharmacological activities, which could differ from those of GSEE or RES alone. This underscores the multifaceted nature of grape extracts and their potential therapeutic applications in addressing sleep disorders and neurodegenerative conditions associated with A{beta} deposition.

Loss of MEF2C function by enhancer mutation leads to neuronal mitochondria dysfunction and motor deficits in mice
Genetic changes and epigenetic modifications are associated with neuronal dysfunction in the pathogenesis of neurodegenerative disorders. However, the mechanism behind genetic mutations in the non-coding region of genes that affect epigenetic modifications remains unclear. Here, we identified an ALS-associated SNP located in the intronic region of MEF2C (rs304152), residing in a putative enhancer element, using convolutional neural network. The enhancer mutation of MEF2C reduces own gene expression and consequently impairs mitochondrial function in motor neurons. MEF2C localizes and binds to the mitochondria DNA, and directly modulates mitochondria-encoded gene expression. CRISPR/Cas-9-induced mutation of the MEF2C enhancer decreases expression of mitochondria-encoded genes. Moreover, MEF2C mutant cells show reduction of mitochondrial membrane potential, ATP level but elevation of oxidative stress. MEF2C deficiency in the upper and lower motor neurons of mice impairs mitochondria-encoded genes, and leads to mitochondrial metabolic disruption and progressive motor behavioral deficits. Together, MEF2C dysregulation by the enhancer mutation leads to mitochondrial dysfunction and oxidative stress, which are prevalent features in motor neuronal damage and ALS pathogenesis. This genetic and epigenetic crosstalk mechanism provides insights for advancing our understanding of motor neuron disease and developing effective treatments.

Actions obey Weber's law when precision is evaluated at goal attainment
Weber's law, the psychophysical principle stating that the just noticeable difference (JND), which is inversely related to sensory precision, increases proportionally with the magnitude of a stimulus, impacts all domains of human perception, but it is violated in visually guided grasping actions. The underlying reasons for this dissociation between perception and action are still debated, and various hypotheses have been put forward, including a different coding of visual size information for perception and action, the use of positional information to guide grasping, biomechanical factors, or sensorimotor calibration. To contrast these hypotheses, we investigated Weber's law in a new action task, the two-finger pointing task. Participants reached and touched two targets positioned at different distances apart by using their index finger and thumb. Consistent with Weber's law, we found that the standard deviation (SD) of the final inter-finger separation, serving as a measure analogous to the JND, increased with larger inter-target distances. These findings suggest that, when considering measures strongly related with the attainment of the action goal, Weber's law is regularly at play.

Mistargeted retinal axons form synaptically segregated subcircuits in the visual thalamus of albino mice
A Hebbian model of circuit remodeling predicts that two sets of inputs with sufficiently distinct activity patterns will synaptically capture separate sets of target cells. Mice in which a subset of retinal ganglion cells (RGCs) target the wrong region of the dorsal lateral geniculate nucleus (dLGN) provide the conditions for testing this prediction. In albino mice, mistargeted RGC axons form an island of terminals that is distinct from the surrounding neuropil. Blocking retinal activity during development prevents the formation of this island. However, the synaptic connectivity of the island was unknown. Here, we combine light and electron microscopy to determine if this activity-dependent island of axon terminals represent a synaptically segregated subcircuit. We reconstructed the microcircuitry of the boundary between the island and non-island RGCs and found a remarkably strong segregation within retinogeniculate connectivity. We conclude that, when sets of retinal input are established in the wrong part of the dLGN, the developing circuitry responds by forming a synaptically isolated subcircuit from the otherwise fully connected network. The fact that there is a developmental starting condition that can induce a synaptically segregated microcircuit has important implications for our understanding of the organization of visual circuits and for our understanding of the implementation of activity dependent development.

Human Brain Barcodes
Dynamic CpG methylation barcodes were read from 15,000 to 21,000 single cells from three human male brains. To overcome sparse sequencing coverage, the barcode had ~31,000 rapidly fluctuating X-chromosome CpG sites (fCpGs), with at least 500 covered sites per cell and at least 30 common sites between cell pairs (average of ~48). Barcodes appear to start methylated and record mitotic ages because excitatory neurons and glial cells that emerge later in development were less methylated. Barcodes are different between most cells, with average pairwise differences (PWDs) of ~0.5 between cells. About 10 cell pairs per million were more closely related with PWDs < 0.05. Barcodes appear to record ancestry and reconstruct trees where more related cells had similar phenotypes, albeit some pairs had phenotypic differences. Inhibitory and excitatory neurons both showed evidence of tangential migration with related cells in different cortical regions. fCpG barcodes become polymorphic during development and can distinguish between thousands of human cells.

HINT1 Inhibitors as Selective Modulators of MOR-NMDAR Cross Regulation and Non-Opioid Analgesia
The Human Histidine Triad Nucleotide Binding Protein 1 (HINT1) has recently become a protein of interest due to its involvement in several CNS processes, including neuroplasticity and the development of several neuropsychiatric disorders. Crucially, HINT1 behaves as a mediator for the cross-regulation of the mu opioid receptor (MOR) and N-methyl-D-aspartate receptor (NMDAR). Active site inhibition of HINT1 using small molecule inhibitors has been demonstrated to have a significant impact on this cross-regulatory relationship in vivo. Herein, we describe the development of a series of ethenoadenosine HINT1 inhibitors to further evaluate the effect of HINT1 inhibition on morphines blockade of NMDA-evoked behaviors, the development of acute endomorphin-2 tolerance and analgesia. X-ray crystallographic analysis and HINT1 binding experiments demonstrate that modifications to the inhibitor nucleobase greatly impact the inhibitor binding interactions with HINT1. Our results reveal a complex structural-activity relationship for HINT1 inhibitors in which minor modifications to the ethenoadenosine scaffold resulted in dramatic changes to their activity in these assays modeling MOR-NMDAR interaction. Specifically, we observed the ability of HINT1 inhibitors to selectively affect individual pathways of MOR-NMDAR crosstalk. Furthermore, we observed that a carbamate ethenoadenosine inhibitor of HINT1 can induce analgesia, while not affecting opioid tolerance. Additionally, although past studies have indicated that that loss of HINT1 expression can result in the downregulation of p53, we have shown that inhibition of HINT1 has no effect on either the expression of HINT1 or p53. These studies highlight the critical role of HINT1 in MOR-NMDAR crosstalk and demonstrate the intriguing potential of using HINT1 active-site inhibitors as tools to probe its role in these biochemical pathways and its potential as a novel pain target.

Primary auditory thalamus relays directly to cortical layer 1 interneurons
Inhibitory interneurons within cortical layer 1 (L1-INs) integrate inputs from diverse brain regions to modulate sensory processing and plasticity, but the sensory inputs that recruit these interneurons have not been identified. Here we used monosynaptic retrograde tracing and whole-cell electrophysiology to characterize the thalamic inputs onto two major subpopulations of L1-INs in the mouse auditory cortex. We find that the vast majority of auditory thalamic inputs to these L1-INs unexpectedly arise from the ventral subdivision of the medial geniculate body (MGBv), the tonotopically-organized primary auditory thalamus. Moreover, these interneurons receive robust functional monosynaptic MGBv inputs that are comparable to those recorded in the L4 excitatory pyramidal neurons. Our findings identify a direct pathway from the primary auditory thalamus to the L1-INs, suggesting that these interneurons are uniquely positioned to integrate thalamic inputs conveying precise sensory information with top-down inputs carrying information about brain states and learned associations.

Prefrontal metabolite alterations in individuals with posttraumatic stress disorder: a 7T magnetic resonance spectroscopy study
Background: Evidence from animal and human studies suggests glutamatergic dysfunction in posttraumatic stress disorder (PTSD). The purpose of this study was to investigate glutamate abnormalities in the dorsolateral prefrontal cortex (DLFPC) of individuals with PTSD using 7T MRS, which has better spectral resolution and signal-to-noise ratio than lower field strengths, thus allowing for better spectral quality and higher sensitivity. We hypothesized that individuals with PTSD would have lower glutamate levels compared to trauma-exposed individuals without PTSD and individuals without trauma exposure. Additionally, we explored potential alterations in other neurometabolites and the relationship between glutamate and psychiatric symptoms. Methods: Individuals with PTSD (n=27), trauma-exposed individuals without PTSD (n=27), and individuals without trauma exposure (n=26) underwent 7T MRS to measure glutamate and other neurometabolites in the left DLPFC. The severities of PTSD, depression, anxiety, and dissociation symptoms were assessed. Results: We found that glutamate was lower in the PTSD and trauma-exposed groups compared to the group without trauma exposure. Furthermore, N-acetylaspartate (NAA) was lower and lactate was higher in the PTSD group compared to the group without trauma exposure. Glutamate was negatively correlated with depression symptom severity in the PTSD group. Glutamate was not correlated with PTSD symptom severity. Conclusion: In this first 7T MRS study of PTSD, we observed altered concentrations of glutamate, NAA, and lactate. Our findings provide evidence for multiple possible pathological processes in individuals with PTSD. High-field MRS offers insight into the neurometabolic alterations associated with PTSD and is a powerful tool to probe trauma- and stress-related neurotransmission and metabolism in vivo.

The Neurobiology of Cognitive Fatigue and Its Influence on Effort-Based Choice
Feelings of cognitive fatigue emerge through repeated mental exertion and are ubiquitous in our daily lives. However, there is a limited understanding of the neurobiological mechanisms underlying the influence of cognitive fatigue on decisions to exert. We use functional magnetic resonance imaging to examine brain activity while participants make choices to exert effort for reward, before and after bouts of fatiguing cognitive exertion. We found that when participants became cognitively fatigued, they were more likely to choose to forgo higher levels of reward that required more effort. We describe a mechanism by which signals related to cognitive exertion in dlPFC influence effort value computations, instantiated by the insula, thereby influencing an individual's decisions to exert while fatigued. Our results suggest that cognitive fatigue plays a critical role in decisions to exert effort and provides a mechanistic link through which information about cognitive state shapes effort-based choice.

SV2A is expressed in synapse subpopulations in mouse and human brain: implications for PET radiotracer studies
Synapse pathology is a feature of most brain diseases and there is a pressing need to monitor the onset and progression of this pathology using brain imaging in living patients. A major step toward this goal has been the development of small-molecule radiotracers that bind to synaptic vesicle glycoprotein 2A (SV2A) for use in positron emission tomography (PET). Changes in SV2A radiotracer binding in PET are widely interpreted to report differences in the density of all synapses throughout brain regions. Here, we analyse the expression of SV2A at single-synapse resolution across regions of adult mouse and human brain. We find that SV2A is expressed in fewer than 50% of excitatory and inhibitory synapses and that the density of SV2A-positive synapses differs between brain regions. Furthermore, individual synapses differ in their amounts of SV2A. These findings have important implications for the interpretation of PET imaging studies in a clinical setting and point to the need for a detailed understanding of SV2A synaptome architecture in both healthy brain and disease cases where PET imaging is being applied.

Resistance to age-related hearing loss in the echolocating big brown bat (Eptesicus fuscus)
Hearing mediates many behaviors critical for survival in echolocating bats, including foraging and navigation. Most mammals are susceptible to progressive age-related hearing loss; however, the evolution of biosonar, which requires the ability to hear low-intensity echoes from outgoing sonar signals, may have selected against the development of hearing deficits in echolocating bats. Although many echolocating bats exhibit exceptional longevity and rely on acoustic behaviors for survival to old age, relatively little is known about the aging bat auditory system. In this study, we used DNA methylation to estimate the ages of wild-caught big brown bats (Eptesicus fuscus) and measured hearing sensitivity in young and aging bats using auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs). We found no evidence for hearing deficits in aging bats, demonstrated by comparable thresholds and similar ABR wave and DPOAE amplitudes across age groups. We additionally found no significant histological evidence for cochlear aging, with similar hair cell counts, afferent, and efferent innervation patterns in young and aging bats. Here we demonstrate that big brown bats show minimal evidence for age-related loss of peripheral hearing sensitivity and therefore represent informative models for investigating mechanisms that may preserve hearing function over a long lifetime.

Automatic dendritic spine segmentation in widefield fluorescence images reveal synaptic nanostructures distribution with super-resolution imaging
Dendritic spines are the main sites for synaptic communication in neurons, and alterations in their density, size, and shapes occur in many brain disorders. Current spine segmentation methods perform poorly in conditions with low signal-to-noise and resolution, particularly in the widefield images of thick (over 10 m) brain slices. Here, we combined two open-source machine-learning models to achieve automatic 3D spine segmentation in widefield diffraction-limited fluorescence images of neurons in thick brain slices. We validated the performance by comparison with manually segmented super-resolution images of spines reconstructed from direct stochastic optical reconstruction microscopy (dSTORM). Lastly, we show an application of our approach by combining spine segmentation from diffraction-limited images with dSTORM of synaptic protein PSD-95 in the same field-of-view. This allowed us to automatically analyze and quantify the nanoscale distribution of PSD-95 inside the spine. Importantly, we found the numbers, but not the average sizes, of synaptic nanomodules and nanodomains increase with spine size.

Visual field asymmetries in responses to ON and OFF pathway biasing stimuli
Recent reports suggest the ON and OFF pathways are differentially susceptible to selective vision loss in glaucoma. Thus, perimetric assessment of ON- and OFF-pathway function may serve as a useful diagnostic. However, this necessitates a developed understanding of normal ON/OFF pathway function around the visual field and as a function of input intensity. Here, using electroencephalography, we measured ON- and OFF-pathway biased contrast response functions in the upper and lower visual fields. Using the steady-state visually evoked potential paradigm, we flickered achromatic luminance probes according to a saw-tooth waveform, the fast-phase of which biased responses towards the ON or OFF pathways. Neural responses from the upper and lower visual fields were simultaneously measured using frequency tagging - probes in the upper visual field modulated at 3.75Hz, while those in the lower visual field modulated at 3Hz. We find that responses to OFF/decrements are larger than ON/increments, especially in the lower visual field. In the lower visual field, both ON and OFF responses were well described by a sigmoidal non-linearity. In the upper visual field, the ON pathway function was very similar to that of the lower, but the OFF pathway function showed reduced saturation and more cross-subject variability. Overall, this demonstrates that the relationship between the ON and OFF pathways depends on the visual field location and contrast level, potentially reflective of natural scene statistics.