bioRxiv Subject Collection: Neuroscience's Journal

Harnessing Synaptic Vesicle Release and Recycling Mechanism for Molecule Delivery to Neurons
Neurodegenerative clinical trials often fail due to insufficient drug doses in reaching targeted cells and the unintended delivery to non-targeted cells. This study demonstrates an alternative neuron-selective drug delivery system, which utilizes the synaptic vesicle release and recycling mechanism (SVRM) by antibody shuttles targeting synaptic vesicle transmembrane proteins for molecule delivery. Using Synaptotagmin-2 (SYT2), we exemplify that intravenously administered anti-SYT2 antibodies localize to neuromuscular junctions, undergo uptake, and retrograde transport to ChAT-positive motor neurons (MNs) in the spinal cord and brainstem. The delivery of anti-microtubule agent and Malat1 gapmer antisense oligonucleotide to MNs with anti-SYT2 antibodies induces axon degeneration and reduction of Malat1 RNA expression, respectively. This approach circumvents the blood-spinal cord barrier, enabling selective delivery of therapeutic molecules to neurons while minimizing effects in non-targeted cells. Thus harnessing SVRM presents a promising strategy for enhancing drug concentrations in neurons and improving treatment efficacy for neurodegenerative diseases.

Multiple mechanisms of action of an extremely painful venom
Evolutionary arms races between predator and prey can lead to extremely specific and effective defense mechanisms. Such defenses include venoms that deter predators by targeting nociceptive (pain-sensing) pathways. Through co-evolution, venom toxins can become extremely efficient modulators of their molecular targets. The venom of velvet ants (Hymenoptera: Mutillidae) is notoriously painful. The intensity of a velvet ant sting has been described as "Explosive and long lasting, you sound insane as you scream. Hot oil from the deep fryer spilling over your entire hand." The effectiveness of the velvet ant sting as a deterrent against potential predators has been shown across vertebrate orders, including mammals, amphibians, reptiles, and birds. The venom's low toxicity suggests it has a targeted effect on nociceptive sensory mechanisms. This leads to the hypothesis that velvet ant venom targets a conserved nociception mechanism, which we sought to uncover using Drosophila melanogaster as a model system. Drosophila larvae have peripheral sensory neurons that sense potentially damaging (noxious) stimuli such as high temperature, harsh mechanical touch, and noxious chemicals. These polymodal nociceptors are called class IV multidendritic dendritic arborizing (cIV da) neurons, and they share many features with vertebrate nociceptors, including conserved sensory receptor channels. We found that velvet ant venom strongly activated Drosophila nociceptors through heteromeric Pickpocket/Balboa (Ppk/Bba) ion channels. Furthermore, we found a single venom peptide (Do6a) that activated larval nociceptors at nanomolar concentrations through Ppk/Bba. Drosophila Ppk/Bba is homologous to mammalian Acid Sensing Ion Channels (ASICs). However, the Do6a peptide did not produce behavioral signs of nociception in mice, which was instead triggered by other non-specific, less potent, peptides within the venom. This suggests that Do6a is an insect-specific venom component that potently activates insect nociceptors. Consistent with this, we showed that the velvet ant's defensive sting produced aversive behavior in a predatory praying mantis. Together, our results indicate that velvet ant venom evolved to target nociceptive systems of both vertebrates and invertebrates, but through different molecular mechanisms.

Loss of neuropeptidergic regulation of cholinergic transmission induces CaV1-mediated homeostatic compensation in muscle cells
Chemical synaptic transmission at the neuromuscular junction (NMJ) is regulated by electrical activity of the motor circuit, but may also be affected by neuromodulation. Here, we assess the role of neuropeptide signaling in the plasticity of NMJ function in Caenorhabditis elegans. We show that the CAPS (Ca2+-dependent activator protein for secretion) ortholog UNC-31, which regulates the exocytosis of dense core vesicles (DCVs), affects both pre- and post-synaptic functional properties, as well as NMJ-mediated locomotion. Despite reduced evoked acetylcholine transmission, the loss of unc-31 results in a more vigorous response to presynaptic stimulation, i.e., enhanced muscle contraction and Ca2+ transients. Based on expression profiles, we identified neuropeptides involved in both cholinergic (FLP-6, NLP-9, NLP-21 and NLP-38) and GABAergic motor neurons (FLP-15, NLP-15), that mediate normal transmission at the NMJ. In the absence of these peptides, neurons fail to upregulate their transmitter output in response to increased cAMP signaling. We also identified proprotein convertases encoded by aex-5/kpc-3 and egl-3/kpc-2 that act synergistically to generate these neuropeptides. We propose that postsynaptic homeostatic scaling, mediated by increased muscle excitability, could compensate for the reduced cholinergic transmission in mutants affected for neuropeptide signaling, thus maintaining net synaptic strength. We show that in the absence of UNC-31 muscle excitability is modulated by upregulating the expression of the muscular L-type voltage-gated Ca2+ channel EGL-19 (CaV1). Collectively, our results unveil a role for neuropeptidergic regulation in synaptic plasticity, linking changes in presynaptic transmission to compensatory changes in muscle excitability.

Integration of binocular vision and motor state to promote prey pursuit
Most animals with two eyes combine the inputs to achieve binocular vision, which can serve numerous functions, and is particularly useful in hunting prey. However, the mechanisms by which visual information from the two eyes are combined remain largely unknown. To address this question, we identified the binocular neurons that respond to prey in zebrafish (bino-PRNs). These neurons respond specifically to prey, and their activity is enhanced during hunting. To explore the relationship between bino-PRNs and hunting, we optogenetically induced hunting and found that the bino-PRNs receive excitatory input during hunting. To determine the role of the bino-PRNs in behavior, we optogenetically activated them, and found that they promote forward prey capture swims. Our results support a model where bino-PRNs integrate sensory information from the two eyes with hunting state information to drive approach toward prey in the binocular zone.

The epitranscriptomic m6A RNA modification modulates synaptic function in ageing and in a mouse model of synucleinopathy
N6-methyladenosine (m6A) is the most abundant and conserved transcriptional modification in eukaryotic RNA, regulating RNA fate. While the functions of m6A in the development of the mammalian brain have been extensively studied, its roles in synaptic plasticity, cognitive decline, motor function, or other brain circuits remain underexplored. To date, the role of this modification in Parkinson's disease (PD) and other synucleinopathies has been largely unknown. Here, we investigated the m6A epitranscriptome in a mouse model of synucleinopathy. We performed m6A RNA immunoprecipitation sequencing (meRIP-seq) to obtain the m6A epitranscriptome of the midbrain in young (3 mo) and aged (15 mo) A30P-aSyn transgenic mice (aSyn Tg) and C57BL6 control wild type (Wt) mice. We observed hypermethylation of synaptic genes in 3 mo aSyn Tg mice compared to age-matched Wt mice. This methylation was reduced during ageing, with synaptic genes becoming increasingly hypomethylated. Using immunofluorescence imaging alongside biochemical analysis, we further investigated the expression of m6A regulatory enzymes writer, N6-Adenosine-Methyltransferase Complex Catalytic Subunit (METTL3); reader, YTH N6-methyladenosine RNA-binding protein (YTHDF1); and eraser, fat mass and obesity-associated protein (FTO) in the cortex, striatum, hippocampus, and cerebellum of Wt and aSyn Tg mice, as well as in primary cortical neuronal cultures. We observed that the levels of METTL3, YTHDF1 and FTO were similar between Wt and aSyn Tg mice. Interestingly, the writer protein METTL3 was found in both the nucleus and in the post-synaptic compartment in neuronal cultures. Our findings suggest that alterations in the regulation of m6A RNA methylation may be associated with neurodegeneration and ageing and that this level of epitranscriptomic regulation plays a significant role at the synapse.

Neural Dynamics Underlying False Alarms in Extrastriate Cortex
The unfolding of neural population activity can be approximated as a dynamical system. Stability in the latent dynamics that characterize neural population activity has been linked with consistency in animal behavior, such as motor control or value-based decision-making. However, whether similar dynamics characterize perceptual activity and decision-making in the visual cortex is not well understood. To test this, we recorded V4 populations in monkeys engaged in a non-match-to-sample visual change-detection task that required sustained engagement. We measured how the stability in the latent dynamics in V4 might affect monkeys' perceptual behavior. Specifically, we reasoned that unstable sensory neural activity around dynamic attractor boundaries may make animals susceptible to taking incorrect actions when withholding action would have been correct ("false alarms"). We made three key discoveries: 1) greater stability was associated with longer trial sequences; 2) false alarm rate decreased (and reaction times slowed) when neural dynamics were more stable; and, 3) low stability predicted false alarms on a single-trial level, and this relationship depended on the elapsed time during the trial, consistent with the latent neural state approaching an attractor boundary. Our results suggest the same outward false alarm behavior can be attributed to two different potential strategies that can be disambiguated by examining neural stability: 1) premeditated false alarms that might lead to greater stability in population dynamics and faster reaction time and 2) false alarms due to unstable sensory activity consistent with misperception.

The serotonergic psychedelic DOI impairs deviance detection in the auditory cortex
Psychedelics are known to induce profound perceptual distortions, yet the neural mechanisms underlying these effects, particularly within the auditory system, remain poorly understood. In this study, we investigated the effects of the psychedelic compound 2,5-Dimethoxy-4-iodoamphetamine (DOI), a serotonin 2A receptor agonist, on the activity of neurons in the auditory cortex of awake mice. We examined whether DOI administration alters sound-frequency tuning, variability in neural responses, and deviance detection (a neural process reflecting the balance between top-down and bottom-up processing). Our results show that while DOI does not alter the frequency selectivity of auditory cortical neurons in a consistent manner, it increases trial-by-trial variability in responses and consistently diminishes the neural distinction between expected (standard) and unexpected (oddball) stimuli. This reduction in deviance detection was primarily driven by a decrease in the response to oddball sounds, suggesting that DOI dampens the auditory cortex's sensitivity to unexpected events. These findings provide insights into how psychedelics disrupt sensory processing and shed light on the neural mechanisms underlying the altered perception of auditory stimuli observed in the psychedelic state.

Inhibition mediated by group III mGluRs regulates habenula activity and defensive behaviors
Inhibition contributes to various brain computations from sensory motor transformations to cognitive operations. While most studies on inhibition focus on GABA, the main excitatory neurotransmitter of the brain, glutamate, can also elicit inhibition via metabotropic glutamate receptors (mGluRs). The function of mGluR-mediated inhibition remains largely elusive. Here, we investigated the role of group III mGluR-dependent inhibition in the habenula. This primarily glutamatergic and conserved forebrain region acts as a hub between multiple forebrain inputs and neuromodulatory mid- and hindbrain targets that regulate adaptive behaviors. We showed that both zebrafish and mice habenula express group III mGluRs. We identified that group III mGluRs regulate the membrane potential and calcium activity of zebrafish dorsal habenula. Pharmacological and genetic perturbation of group III mGluRs increased sensory-evoked excitation and reduced selectivity of habenular neurons to different sensory modalities. We also observed that inhibition is the main channel of communication between primarily glutamatergic habenula neurons. Blocking group III mGluRs reduced inhibition within habenula and increased correlations during spontaneous activity. In line with such inhibition within habenula, we identified that multi-sensory information is integrated mainly through competition and suppression across habenular neurons, which in part relies on group III mGluRs. Finally, genetic perturbation of a habenula-specific group III mGluR, mGluR6a, amplified neural responses and defensive behaviors evoked by sensory stimulation and environmental changes. Altogether, our results revealed that mGluR driven inhibition is essential in encoding, integration, and communication of information between Hb neurons, ultimately playing a critical role in regulating defensive and adaptive behaviors.

Single cone photoreceptors experience global image statistics through gaze shifts
Our visual experience does not merely reflect a static view of the world but is a dynamic consequence of our actions, most notably our continuously shifting gaze. These shifts determine the spectral diet of any individual cone photoreceptor. The aim of this study was to characterize that diet and its relationship to scene adaptation. Gaze shifts were recorded from observers freely viewing scenes outdoors for five minutes. Hyperspectral images of the scenes were also recorded from the eye position of observers. As a control, gaze shifts were also recorded from observers viewing the images on a computer-controlled display in the laboratory. From the hyperspectral data, spatially local histograms of estimated excitations in long-, medium-, and short-wavelength-sensitive cones were accumulated over time at different retinal locations. A global illuminant change was then introduced to test how well local retinal adaptation discounted its effects. The results suggest that over short periods individual cones tend to experience the statistics of full scenes, with local adaptation compensating for illumination changes almost as well as global adaptation. This compensation may help to maintain our stable local perception of scene colour despite changes in scene illumination.

Positive Allosteric Modulation of the α5-GABAA receptors prevents neuronal atrophy and cognitive decline independently of tau tangle accumulation in the PS19 mouse model
Background: Dysregulated tau phosphorylation is one of the hallmarks of Alzheimer's disease (AD), and it results in cognitive impairments, neuronal atrophy, and neurofibrillary tangle accumulation. Evidence shows that impaired somatostatin (SST) expression, particularly in SST-expressing GABAergic neurons, significantly contributes to AD-related pathophysiology and may increase cognitive burden. Additionally, SST+ interneurons in cortical layers and the hippocampus inhibit the dendrites of excitatory neurons, primarily through 5-GABAA receptors involved in cognitive regulation. Leveraging the potential of a newly developed small molecule that targets the 5-GABAA receptors via positive allosteric modulation (5-PAM), we aim to assess its effects on tau phosphorylation-related neuronal morphology, cognitive deficits and protein expression. Methods: In the PS19 transgenic mouse mode, we administered the 5-PAM, GL-II-73, either acutely or chronically at 3 and 6 months. We assessed spatial working memory using the Y-maze. Golgi staining analyzed dendritic morphology in chronically exposed mice to 5-PAM. Western blotting was used to quantify p-Tau and Tau expression. Results: 5-PAM effectively reverses spatial working memory deficits induced by tau phosphorylation both acutely and chronically. Chronic treatment at 3and 6 months mitigates tau-induced loss of spine density. However, 5-PAM does not directly influence p-Tau levels, suggesting cognitive and neurotrophic benefits of GL-II-73s are independent of Tau burden. Conclusions: These results demonstrate the potential for both symptomatic and disease-modifying effects, highlighting the promise of 5-GABAA receptor positive allosteric modulation as a novel therapeutic strategy for addressing cognitive deficits associated with tau phosphorylation in AD pathology.

Anatomically distinct regions in the inferior frontal cortex are modulated by task and reading skill
Inferior frontal cortex (IFC) is a critical region for reading and language. This part of the cortex is highly heterogeneous in its structural and functional organization and shows high variability across individuals. Despite decades of research, the relationship between specific IFC regions and reading skill remains unclear. To shed light on the function of IFC in reading, we aim to (1) characterize the functional landscape of text-selective responses in the IFC, while accounting for interindividual variability; and (2) examine how text-selective regions in the IFC relate to reading proficiency. To this end, children with a wide range of reading ability (N=66; age 7-14 years, 34 female, 32 male) completed functional MRI scans while performing two tasks on text and non-text visual stimuli. Importantly, both tasks do not explicitly require reading, and can be performed on all visual stimuli. This design allows us to tease apart stimulus-driven responses from task-driven responses and examine where in the IFC task and stimulus interact. We were able to identify three anatomically-distinct, text-selective clusters of activation in the IFC, in the inferior frontal sulcus (IFS), and dorsal and ventral precentral gyrus (PrG). These three regions showed a strong task effect that was highly specific to text. Furthermore, text-selectivity in the IFS and dorsal PrG was associated with reading proficiency, such that better readers showed higher selectivity to text. These findings suggest that text-selective regions in the IFC are sensitive to both stimulus and task, and highlight the importance of this region for proficient reading.

Adrenergic C1 neurons enhance anxiety via projections to PAG
Anxiety is an emotional state precipitated by the anticipation of real or potential threats. Anxiety disorders are the most prevalent psychiatric illnesses globally and increase the risk of developing comorbid conditions that negatively impact the brain and body. The etiology of anxiety disorders remains unresolved, limiting improvement of therapeutic strategies to alleviate anxiety-related symptoms with increased specificity and efficacy. Here, we applied novel intersectional tools to identify a discrete population of brainstem adrenergic neurons, named C1 cells, that promote aversion and anxiety-related behaviors via projections to the periaqueductal gray matter (PAG). While C1 cells have traditionally been implicated in modulation of autonomic processes, rabies tracing revealed that they receive input from brain areas with diverse functions. Calcium-based in vivo imaging showed that activation of C1 cells enhances excitatory responses in vlPAG, activity that is exacerbated in times of heightened stress. Furthermore, inhibition of C1 cells impedes the development of anxiety-like behaviors in response to stressful situations. Overall, these findings suggest that C1 neurons are positioned to integrate complex information from the brain and periphery for the promotion of anxiety-like behaviors.

Bullying and Early Brain Development: A Longitudinal Structural Magnetic Resonance Imaging Study from Adolescence to Early Adulthood
To explore this, we conducted the largest structural MRI analysis to date (n=2094, including 1009 females), across three time points from the IMAGEN study, tracking region-specific brain volume trajectories from adolescence to early adulthood using a data-driven approach. Generally, experienced bullying showed increased subcortical volumes in the putamen (beta=0.12), caudate (beta=0.06), accumbens (beta=0.06), amygdala (beta=0.07), hippocampus (beta=0.06), paired with decreased cerebellar (beta=-0.10), entorhinal, (beta=-0.12), and insula (beta=-0.11) volumes. Females exhibited more volumetric changes in emotional processing areas whereas males had more changes in motor and sensory regions. These findings point to widespread associations between bullying victimization and brain development, offering a potential neurobiological framework to explain the emotional and behavioral difficulties observed. Importantly, this study emphasizes the need for a sex-sensitive approach in future research and interventions related to bullying.

Diffusion Wavelets on Connectome: Localizing the Sources of Diffusion Mediating Structure-Function Mapping Using Graph Diffusion Wavelets
The intricate link between brain functional connectivity (FC) and structural connectivity (SC) is explored through models performing diffusion on SC to derive FC, using varied methodologies from single to multiple graph diffusion kernels. However, existing studies have not correlated diffusion scales with specific brain regions of interest (RoIs), limiting the applicability of graph diffusion. We propose a novel approach using graph heat diffusion wavelets to learn the appropriate diffusion scale for each RoI to accurately estimate the SC-FC mapping. Using the open HCP dataset, we achieve an average Pearson's correlation value of 0.833, surpassing the state-of-the-art methods for prediction of FC. It is important to note that the proposed architecture is entirely linear, computationally efficient, and notably demonstrates the power-law distribution of diffusion scales. Our results show that the bilateral frontal pole, by virtue of it having large diffusion scale, forms a large community structure. The finding is in line with the current literature on the role of the frontal pole in resting-state networks. Overall, the results underscore the potential of graph diffusion wavelet framework for understanding how the brain structure leads to functional connectivity.

Controlled retrieval relies on directed interactions between semantic control regions and visual cortex: MEG evidence from oscillatory dynamics
To navigate the world, we store knowledge about the relationships between concepts and retrieve this information flexibly to suit our goals. The semantic control network, comprising left inferior frontal gyrus (IFG) and posterior middle temporal gyrus (pMTG), is thought to orchestrate this flexible retrieval by modulating sensory inputs. However, interactions between semantic control and input regions are not sufficiently understood. Moreover, pMTG's well-formed structural connections to both IFG and visual cortex suggests it as a candidate region to integrate control and input processes. We used magnetoencephalography to investigate oscillatory dynamics during semantic decisions to pairs of words, presented one at a time, when participants did or did not know the type of semantic relation between them. IFG showed early increases and decreases in oscillatory responses to prior task knowledge, while pMTG only showed positive effects of task knowledge at a later time window. Furthermore, both regions provided feedback to visual cortex when goals were absent, while IFG also provided feedback when goals were known. This goal-dependent feedback coincided with an earlier onset of feedforward signalling from visual cortex to pMTG, indicating rapid retrieval of task-relevant features. Knowledge of task goals also enhanced simultaneous inputs to pMTG from both IFG and visual cortex, consistent with the view that pMTG integrates top-down control with bottom-up input. Our findings elucidate the separate roles of anterior and posterior components of the semantic control network and reveal the spectro-temporal cascade of interactions between semantic control and visual regions that underlie our ability to flexibly adapt cognition to the current goals.

Sympathetic innervation of interscapular brown adipose tissue is not a predominant mediator of OT-elicited reductions of body weight gain and adiposity in male diet-induced obese rats
Recent studies indicate that central administration of oxytocin (OT) reduces body weight (BW) in high fat diet-induced obese (DIO) rodents by reducing energy intake and increasing energy expenditure (EE). Previous studies in our lab have shown that administration of OT into the fourth ventricle (4V; hindbrain) elicits weight loss and stimulates interscapular brown adipose tissue temperature (TIBAT) in DIO rats. We hypothesized that OT-elicited stimulation of sympathetic nervous system (SNS) activation of IBAT contributes to its ability to activate BAT and reduce BW in DIO rats. To test this, we determined the effect of disrupting SNS activation of IBAT on OT-elicited stimulation of TIBAT and reduction of BW in DIO rats. We first confirmed that bilateral surgical SNS denervation to IBAT was successful based on having achieved [≥] 60% reduction in IBAT norepinephrine (NE) content from DIO rats. NE content was selectively reduced in IBAT by 94.7 {+/-} 2.7, 96.8 {+/-} 1.8 and 85.9 {+/-} 6.1% (P<0.05) at 1, 6 and 7-weeks post-denervation, respectively, and was unchanged in liver or inguinal white adipose tissue. We then measured the impact of bilateral surgical SNS denervation to IBAT on the ability of acute 4V OT (1, 5 g) to stimulate TIBAT in DIO rats. We found that the high dose of 4V OT (5 g) stimulated TIBAT similarly between sham and denervated rats (P=NS) and that the effects of 4V OT to stimulate TIBAT did not require beta-3 adrenergic receptor signaling. We subsequently measured the effect of bilateral surgical denervation of IBAT on the effect of chronic 4V OT (16 nmol/day) or vehicle infusion to reduce BW, adiposity and energy intake in DIO rats. Chronic 4V OT reduced BW gain by -7.2 {+/-} 9.6 g and -14.1 {+/-} 8.8 g in sham and denervated rats (P<0.05 vs vehicle treatment), respectively, and this effect was similar between groups (P=NS). These effects were associated with reductions in adiposity and energy intake (P<0.05). Collectively, these findings support the hypothesis that sympathetic innervation of IBAT is not required for central OT to increase BAT thermogenesis and reduce BW gain and adiposity in male DIO rats.

Phenotype Prediction Using BEN-Based Predictive Modeling (BPM)
Functional connectivity (FC) has been successfully used to predict cognitive functions, behaviors, and other phenotypes using connectome-based predictive modeling (CPM). One limitation is that FC reflects the covariation or synchrony relationship of the temporal profile in two regions and neglects the local temporal features of the brain activity. In this study, we used brain entropy (BEN) mapping to characterize regional brain activity and developed a BEN-Based Predictive Modeling (BPM) to predict phenotype. BEN measures the disorder and complexity of brain activity and has been shown to effectively capture brain activity features related to cognition and neurological disorders. Using data from the HCP 7T fMRI and corresponding 3T structural images, we calculated gray matter volume (GMV) as well as BEN from resting state and movie-watching data. We constructed prediction models based on BEN and GMV using different numbers of parcellation of the brain atlas, applying 10-fold cross-validation. Our results indicated that the BEN-based predictive model not only outperformed GMV-based predictive modeling but also achieved prediction accuracy comparable to that of CPM. Our study demonstrates that BEN can capture extensive brain activity information for accurate phenotype prediction, providing information at least as valuable as that from connectome. Additionally, our research lays the groundwork for future applications of BPM in developmental and clinical practice.

Development of sensorimotor responses in larval zebrafish: a comparison between wild-type and GCaMP6s transgenic line
During early development, zebrafish larvae exhibit stereotypical behaviors, which rapidly become more complex. Thus, the generation of mutant transgenic lines that maintain transparency throughout their larval stage and that can be used to record brain activity has offered strategic opportunities to investigate the underlying neural correlates of behavior establishment. However, few studies have documented the behavioral profile of these lines during larval development. Here, we set up a behavioral characterization using diverse stimuli (light and vibration) throughout larval development to compare the responses of a transgenic strain expressing a pan-neuronal calcium indicator (GCaMP6s) with that of a wild-type strain. Interestingly, we report a drastic switch in behavioral responses to light transitions at 11 days post-fertilization (dpf) and to vibration stimuli at 14 dpf in both lines. These data highlight a specific time window of behavioral complexification. Meanwhile, we found no major difference in the maturation of sensorimotor responses between GCaMP6s and wild-type strains. Thus, these results support using GCaMP6s strain in investigating the neural mechanisms underlying the developmental maturation of sensorimotor responses. We observed nevertheless some minor differences that suggest careful attention should be taken when using mutant/transgenic lines for behavioral studies.

Predicting speech-in-noise ability with static and dynamic auditory figure-ground analysis using structural equation modelling
Auditory figure-ground paradigms assess the ability to extract a foreground figure from a random background, a crucial part of central hearing. Previous studies have shown that the ability to extract static figures (with fixed frequencies) predicts real-life listening: speech-in-noise ability. In this study we assessed both fixed and dynamic figures: the latter comprised component frequencies that vary over time like natural speech. 159 participants (aged 18-79) with a range of peripheral hearing sensitivity were studied. We used hierarchal linear regression and structural equation modelling to examine how well speech-in-noise ability (for words and sentences) could be predicted by age, peripheral hearing, and static and dynamic figure-ground. Regression demonstrated that in addition to the audiogram and age, the low-frequency dynamic figure-ground accounted for significant variance of speech-in-noise, higher than the static figure-ground. The structural models showed that a combination of all types of figure-ground tasks predicted speech-in-noise with a higher effect size than the audiogram or age. Age influenced word perception in noise directly but sentence perception indirectly via effects on peripheral and central hearing. Overall, this study demonstrates that dynamic figure-ground explains more variance of real-life listening than static figure-ground, and the combination of both predicts real-life listening better than hearing sensitivity or age.

Stronger premicrosaccadic sensitivity enhancement for dark contrasts in the primate superior colliculus
Microsaccades are associated with enhanced visual perception and neural sensitivity right before their onset, and this has implications for interpreting experiments involving the covert allocation of peripheral spatial attention. However, the detailed properties of premicrosaccadic enhancement are not fully known. Here we investigated how such enhancement in the superior colliculus depends on luminance polarity. Rhesus macaque monkeys fixated a small spot while we presented either dark or bright image patches of different contrasts within the recorded neurons' response fields. Besides replicating premicrosaccadic enhancement of visual sensitivity, we observed stronger enhancement for dark contrasts. This was especially true at moderate contrast levels (such as 10-20%), and it occurred independent of an individual neuron's preference for either darks or brights. On the other hand, postmicrosaccadic visual sensitivity suppression was similar for either luminance polarity. Our results reveal an intriguing asymmetry in the properties of perimicrosaccadic modulations of superior colliculus visual neural sensitivity.

Mutations in PSEN1 predispose inflammation in an astrocyte model of familial Alzheimer's disease through disrupted regulated intramembrane proteolysis
Mutations in PSEN1 cause familial Alzheimer's disease with almost complete penetrance. Age at onset is highly variable between different PSEN1 mutations and even within families with the same mutation. Current research into late onset Alzheimer's disease implicates inflammation in both disease onset and progression. PSEN1 is the catalytic subunit of gamma-secretase, responsible for regulated intramembrane proteolysis of numerous substrates that include cytokine receptors. For this reason, we tested the hypothesis that mutations in PSEN1 impact inflammatory responses in astrocytes, thereby contributing to disease progression. Here, using iPSC-astrocytes, we show that PSEN1 is upregulated in response to inflammatory stimuli, and this upregulation is disrupted by pathological PSEN1 mutations. Using transcriptomic analyses, we demonstrate that PSEN1 mutant astrocytes have an augmented inflammatory profile in their basal state, concomitant with an upregulation of genes coding for regulated intramembrane proteolytic and robust activation of JAK-STAT signalling. Using JAK-STAT2 as an example signalling pathway, we show altered phosphorylation cascades in PSEN1 mutant astrocytes, reinforcing the notion of altered cytokine signalling cascades. Finally, we use small molecule modulators of gamma-secretase to confirm a role for PSEN1/gamma-secretase in regulating the astrocytic response to inflammatory stimuli. Together, these data suggest that mutations in PSEN1 enhance cytokine signalling via impaired regulated intramembrane proteolysis, thereby predisposing astrocytic inflammatory profiles. These findings support a two-hit contribution of PSEN1 mutations to fAD pathogenesis, not only impacting APP and Abeta processing but also altering the cellular response to inflammation.

Barcode activity in a recurrent network model of the hippocampus enables efficient memory binding
Forming an episodic memory requires binding together disparate elements that co-occur in a single experience. One model of this process is that neurons representing different components of a memory bind to an "index" --- a subset of neurons unique to that memory. Evidence for this model has recently been found in chickadees, which use hippocampal memory to store and recall locations of cached food. Chickadee hippocampus produces sparse, high-dimensional patterns ("barcodes") that uniquely specify each caching event. Unexpectedly, the same neurons that participate in barcodes also exhibit conventional place tuning. It is unknown how barcode activity is generated, and what role it plays in memory formation and retrieval. It is also unclear how a memory index (e.g. barcodes) could function in the same neural population that represents memory content (e.g. place). Here, we design a biologically plausible model that generates barcodes and uses them to bind experiential content. Our model generates barcodes from place inputs through the chaotic dynamics of a recurrent neural network and uses Hebbian plasticity to store barcodes as attractor states. The model matches experimental observations that memory indices (barcodes) and content signals (place tuning) are randomly intermixed in the activity of single neurons. We demonstrate that barcodes reduce memory interference between correlated experiences. We also show that place tuning plays a complementary role to barcodes, enabling flexible, contextually-appropriate memory retrieval. Finally, our model is compatible with previous models of the hippocampus as generating a predictive map. Distinct predictive and indexing functions of the network are achieved via an adjustment of global recurrent gain. Our results suggest how the hippocampus may use barcodes to resolve fundamental tensions between memory specificity (pattern separation) and flexible recall (pattern completion) in general memory systems.

The neurotrophin artemin and its receptor GFRα3 mediate migraine-like pain via the ion channel TRPM8
Background Migraine has a strong genetic foundation, including both monogenic and polygenic types. The former are rare, with most migraine considered polygenic, supported by genome-wide association studies (GWAS) identifying numerous genetic variants associated with migraine risk. Surprisingly, some of the most common mutations are associated with TRPM8, a non-selective cation channel that is the primary sensor of cold temperatures in primary afferent neurons of the somatosensory system. However, it is unlikely that the temperature sensitivity of TRPM8 underlies its role in migraine pathogenesis. To define the basis of the channels involvement, we reasoned that cellular processes that increase cold sensitivity in the skin, such as the neurotrophin artemin, via its receptor GFR3, also mediate TRPM8-associated migraine-like pain in the meninges. Methods To investigate the role of artemin and GFR3 in preclinical rodent migraine models, we infused nitroglycerin acutely and chronically, and measured changes in periorbital and hind paw mechanical sensitivity in male and female mice lacking GFR3, after neutralization of free artemin with specific monoclonal antibodies, or by systemic treatment with a TRPM8-specific antagonist. Further, in wildtypes and mice lacking either GFR3 or TRPM8, we tested the effects of supradural infusions of a mix of inflammatory mediators, artemin, and a TRPM8-specific agonist on migraine-related pain in mice. Results We find that mechanical allodynia induced by systemic nitroglycerin, or supradural infusion of inflammatory mediators, involves GFR3. In addition, neutralization of circulating artemin reduces the nitroglycerin phenotype, demonstrating the importance of this neurotrophic pathway. Further, we show TRPM8 expression in the meninges and that direct supradural infusion of either a TRPM8-specific agonist or artemin itself produces mechanical allodynia, the latter dependent on TRPM8 and ameliorated by concurrent treatment with sumatriptan. Conclusions These results indicate that neuroinflammatory events in the meninges can produce migraine-like pain in mice via artemin and GFR3, likely acting upstream of TRPM8, providing a novel pathway that may contribute to migraine pathogenesis.

Sex differences in contextual fear expression are associated with altered medial prefrontal cortex activity
Understanding the neural basis of fear expression in rodents has implications for understanding pathological fear responses that characterize posttraumatic stress disorder. Even though posttraumatic stress disorder is more common in females, little is known about the neural circuit interactions supporting fear expression in female rodents. In this study, we were interested in determining whether neural activity associated with the expression of contextual fear differed between males and females within the projections from the medial prefrontal cortex to the ventrolateral periaqueductal gray, and in the medial prefrontal cortex in neurons that do not project to the periaqueductal gray. We infused a viral retrograde tracer into the ventrolateral periaqueductal gray in male and female rats and trained them in a contextual fear conditioning task. The following day rats were re-exposed to the conditioning context and were sacrificed shortly thereafter. Neural activity was measured using EGR1 immunofluorescence. The behavioral results showed that males exhibited higher levels of freezing during the context test than females. Male rats that underwent training and testing showed an increase in the proportion of viral infected cells that express EGR1 in the PL compared to rats that had only received context exposure. Trained female rats were not different than controls, however a direct comparison between sexes was not different. In cells not labeled by the tracer, males showed higher levels of fear-induced EGR1 expression in the prelimbic cortex than females. Conversely, females showed higher levels of EGR1 expression in the infralimbic cortex following testing as compared to males. These results suggest that sex differences in the expression of contextual fear may involve differences in the relative activity levels of the prelimbic and infralimbic cortex.

Population coding of auditory space in the dorsal inferior colliculus persists with altered binaural cues
Sound localization is critical for real-world hearing, such as segregating overlapping sound streams. For optimal flexibility, central representations of auditory space must adapt to peripheral changes in binaural cue availability, such as following asymmetric hearing loss in adulthood. However, whether the mature auditory system can reliably encode spatial auditory representations upon abrupt changes in binaural input is unclear. Here we use 2-photon Ca2+ imaging in awake head-fixed mice to determine how the higher-order shell layers of the inferior colliculus (IC) encode sound source location in the frontal azimuth, under binaural conditions and after acute monaural hearing loss induced by an ear plug ipsilateral to the imaged hemisphere. Spatial receptive fields were typically broad and not exclusively contralateral: Neurons responded reliably to multiple positions in the contra- and ipsilateral hemifields, with preferred positions tiling the entire frontal azimuth. Ear plugging broadened receptive fields and reduced spatial selectivity in a subset of neurons, in agreement with an inhibitory influence of ipsilateral sounds. However ear plugging also enhanced spatial tuning and/or unmasked receptive fields in other neurons, shifting the distribution of preferred angles ipsilaterally with minimal impact on the neuronal population's overall spatial resolution; these effects occurred within 2 hours of ear plugging. Consequently, linear classifiers trained on fluorescence data from control and ear-plugged conditions had similar classification accuracy when tested on held out data from within, but not across hearing conditions. Spatially informative neuronal population codes therefore arise rapidly following monaural hearing loss, in absence of overt experience.

Differential Impact of Multiple Sensory Deprivation on Spatial-coding Cells in Medial Entorhinal Cortex
Spatial navigation depends on anchoring internal spatial maps to external environments, guided by sensory cues such as visual and tactile stimuli. The Medial Entorhinal Cortex (MEC) is crucial for integrating these sensory inputs during the formation of spatial maps. While the responsiveness of many spatial-coding cells to visual stimuli is well-established, the role of tactile sensation in spatial representation is less understood. Rodents primarily gather tactile information through their whiskers, which provide essential spatial and textural details via whisking movements, potentially vital for constructing accurate spatial map. In our study, we employed advanced miniature two-photon microscopy to monitor neural activity in the MEC of freely moving mice subjected to sensory deprivation. Our findings revealed that head direction cells and border cells exhibited impaired spatial representation after either light deprivation or whisker trimming. In contrast, grid cells and speed cells were less affected by whisker trimming compared to visual deprivation, suggesting a stronger dependence on visual cues for these cell types. Notably, distinct subpopulations within each type of spatial-coding cell exhibited varying sensitivity to sensory deprivation-some neurons significantly changed their spatial-coding patterns, while others remained unaffected. This indicates that cells within the MEC may differ in their spatial-coding based on their sensitivity to external sensory inputs. Additionally, we observed a strong correlation between the activity of certain MEC neurons and whisker movement. Collectively, these findings enhance our understanding of how the MEC processes spatial information, particularly in relation to tactile sensation.

Burst firing optimizes invariant coding of natural communication signals by electrosensory neural populations
Accurate perception of objects within the environment independent of context is essential for the survival of an organism. While neurons that respond in an invariant manner to identity-preserving transformations of objects are thought to provide a neural correlate of context-independent perception, how these emerge in the brain remains poorly understood. Here we demonstrate that burst firing in neural populations can give rise to an invariant representation of highly heterogeneous natural communication stimuli. Multi-unit recordings from central sensory neural populations showed that considering burst spike trains led to invariant representations at the population but not the single neuron level. Computational modeling further revealed that optimal invariance is achieved for levels of burst firing seen experimentally. Taken together, our results demonstrate a novel function for burst firing towards establishing invariant representations of sensory input in neural populations.

Virally encoded single-chain antibody fragments targeting alpha-synuclein protect against motor impairments and neuropathology in a mouse model of synucleinopathy
Parkinson's disease (PD) is a neurodegenerative disorder mainly characterized by the loss of dopaminergic neurons from the substantia nigra. Affected neurons exhibit intracellular aggregates primarily composed of misfolded and phosphorylated alpha-synuclein (aSyn). In pathological conditions, this presynaptic protein has been shown to be transmitted from cell to cell in a prion-like manner, which contributes to the progression of the disease. Single-chain variable fragments (scFvs) are small polypeptides derived from the binding domains of antibodies that are less immunogenic and have better tissue penetration compared to full antibodies. In this work, we aimed to demonstrate the potential of extracellular scFvs to slow down the propagation of pathological aSyn in an in vivo model of synucleinopathy. We generated scFvs that target aSyn, and tested two of them in a PD mouse model consisting of transgenic M83 mice injected with human aSyn pre-formed fibrils (PFFs). The sequence encoding each anti-aSyn scFv was cloned in a self-complementary AAV2 viral vector, and purified particles were administered intravenously. CNS expression of either scFv protected against the development of paralysis and limb weakness, in addition to significantly reducing pathologic aggregates of phosphorylated aSyn in the brain. Moreover, in vitro results in human iPSCs-derived dopaminergic neurons suggest that the scFvs can mitigate aSyn spreading by preventing its internalization. Overall, our findings demonstrate that single-chain antibody fragments exhibit strong therapeutic potential in a preclinical mouse model. Thus, our minimally invasive, gene-mediated immunotherapy approach has the potential to serve as an effective treatment for halting the progression of Lewy body diseases.

CLIMATE BRAIN - Questionnaires, Tasks and the Neuroimaging Dataset
Climate change presents a fundamental threat to human populations and ecosystems across the globe. Neuroscience researchers have recently started developing ways to advance research on this topic. However, validated questionnaires, experimental stimuli, and fMRI tasks are still needed. Here we describe the CLIMATE BRAIN dataset, a multimodal collection of questionnaire, behavioural, and neuroimaging data related to climate change, acquired from 160 healthy individuals. In particular, it includes data from (1) various questionnaire measures, including the Inventory of Climate Emotions (ICE); (2) a neuroimaging task for measuring emotional reactions to standardized Emotional Climate Change Stories (ECCS); and (3) a neuroimaging task based on Carbon Emission Task (CET) to measure climate action-taking. For technical validation, we provide image quality metrics and show the evidence for the effectiveness of tasks consistent with prior studies. To our knowledge, the proposed dataset is currently the only publicly available resource specifically designed to investigate human brain responses to climate change.

Neural representation of vocalization self-monitoring in the bat auditory midbrain
During acoustic interaction, mammals, including humans, not only monitor sounds from external sources but also their own vocalizations, the latter of which is known as vocalization feedback monitoring. Yet, it is unclear whether subcortical auditory regions process vocalization feedback. Here, we established an experimental paradigm that allows recording chronically the single-unit activity of the auditory midbrain (inferior colliculus) in freely vocalizing bats. We report that most collicular neurons represented self-produced biosonar vocalizations distinctively from pure tones and vocalization playbacks. Some neurons showed robust excitatory responses to vocalization feedback yet lacked any excitatory response to pure tones covering the entire frequency range of the vocalizations. Surprisingly, some collicular neurons even reversed the response polarity, from vocalization-induced suppression to vocalization-playback-induced excitation. Moreover, approximately a third of the neurons responded faster to self-produced vocalizations than to both vocalization playbacks and pure tones. These findings show that the midbrain inferior colliculus is involved in vocalization feedback processing, an ability suggested to arise locally in the auditory cortex.

LM11a-31 Inhibits p75 Neurotrophin Receptor (p75NTR) Cleavage and is Neuroprotective in a Cell Culture Model of Parkinson's Disease.
The p75 Neurotrophin Receptor (p75NTR) is a multifunctional transmembrane protein that mediates neuronal responses to pathological conditions in specific regions of the nervous system. In many biological contexts, p75NTR signaling is initiated through sequential cleavage of the receptor by - and {gamma}-secretases, which releases receptor fragments for downstream signaling. Our previous work demonstrated that proteolytic processing of p75NTR in this manner is stimulated by oxidative stress in Lund Human Mesencephalic (LUHMES) cells, a dopaminergic neuronal cell line derived from human mesencephalic tissue. Considering the vulnerability of dopaminergic neurons in the ventral mesencephalon to oxidative stress and neurodegeneration associated with Parkinson's disease (PD), we investigated the role of this signaling cascade in neurodegeneration and explored cellular processes that govern oxidative stress-induced p75NTR signaling. In the present study, we provide evidence that oxidative stress induces cleavage of p75NTR by promoting c-Jun N-terminal Kinase (JNK)-dependent internalization of p75NTR from the cell surface. This activation of p75NTR signaling is counteracted by tropomyosin-related kinase (Trk) receptor signaling; however, oxidative stress leads to Trk receptor downregulation, thereby enhancing p75NTR processing. Importantly, we demonstrate that this pathway can be inhibited by LM11a-31, a small molecule modulator of p75NTR, thereby conferring protection against neurodegeneration. Treatment with LM11a-31 significantly reduced p75NTR cleavage and neuronal death associated with oxidative stress. These findings reveal novel mechanisms underlying activation of p75NTR in response to oxidative stress, underscore a key role for p75NTR in dopaminergic neurodegeneration, and highlight p75NTR as a potential therapeutic target for reducing neurodegeneration in PD.