bioRxiv Subject Collection: Neuroscience's Journal

Mapping Kappa Opioid Receptor Binding in Titi Monkeys with 11C-GR103545 PET
Purpose: The kappa opioid receptor (KOR) plays a pivotal role in stress- and anxiety-related behaviors, especially in social separation and bonding. However, KOR modulations in these social contexts are not fully characterized. The coppery titi monkey (Plecturocebus cupreus) has been utilized as a translational animal model for studying the neurobiology of attachment, as they form socially monogamous adult pair bonds. While the PET radiotracer 11C-GR103545 has shown the ability to track KOR activity in other species, it has not been utilized in titi monkeys. This study assessed 11C-GR103545 PET for characterizing KOR activity in vivo and its pharmacological blockade in titi monkeys. Methods: Adult titi monkeys (N=6) underwent 11C-GR103545 PET brain scans at baseline, followed by repeat scans upon administration of a KOR antagonist (CERC-501) and a KOR agonist (U50,488). Region-specific, non-displaceable binding potential (BPND) was calculated, with the cerebellum as the reference region, focusing on 14 brain volumes of interest (VOIs) implicated in social bonding. Results: Baseline 11C-GR103545 uptake characteristics across VOIs were consistent with previous reports in humans and other monkey models. CERC-501 pretreatment led to a significant reduction in BPND (average 55.99%) across several, but not all brain VOIs, with the most notable reduction in the superior frontal gyrus (76.25%). In contrast, U50,488 pretreatment resulted in no significant BPND changes across the VOIs analyzed. Conclusions: This study demonstrates the utility of 11C-GR103545 to assess KOR binding dynamics in a monkey model of social bonding. Region-specific blockade of KOR was observed after pretreatment by CERC-501, while blockade by the KOR agonist U50,488 did not change 11C-GR103545 binding.

Increased vowel contrast and intelligibility in connected speech induced by sensorimotor adaptation
Alterations to sensory feedback can drive robust adaptive changes to the production of consonants and vowels, but these changes often have no behavioral relevance or benefit to communication (e.g., making "head" more like "had"). This work aims to align the outcomes of adaptation with changes known to increase speech intelligibility - specifically, adaptations that increase the acoustic contrast between vowels in running speech. To this end, we implemented a vowel centralization feedback perturbation paradigm that pushes all vowels towards the center of vowel space, making them sound less distinct from one another. Speakers across the adult lifespan adapted to the centralization perturbation during sentence production, increasing the global acoustic contrast among vowels and the articulatory excursions for individual vowels. These changes persisted after the perturbation was removed, including after a silent delay, and showed robust transfer to words that were not present in the sentences. Control analyses demonstrated that these effects were unlikely to be due to explicit pronunciation strategies and occurred in the face of increasingly more rapid and less distinct production of familiar sentences. Finally, sentence transcription by crowd-sourced listeners showed that speakers' vowel contrast predicted their baseline intelligibility and that experimentally-induced increases in contrast predicted intelligibility gains. These findings establish the validity of a sensorimotor adaptation paradigm to implicitly increase vowel contrast and intelligibility in connected speech, an outcome that has the potential to enhance rehabilitation in individuals who present with a reduced vowel space due to motor speech disorders, such as the hypokinetic dysarthria associated with Parkinson's disease.

Investigating cocaine- and abstinence-induced effects on astrocyte gene expression in the nucleus accumbens
In recent years, astrocytes have been increasingly implicated in cellular mechanisms of substance use disorders (SUD). Astrocytes are structurally altered following exposure to drugs of abuse; specifically, astrocytes within the nucleus accumbens (NAc) exhibit significantly decreased surface area, volume, and synaptic colocalization after operant self-administration of cocaine and extinction or protracted abstinence (45 days). However, the mechanisms that elicit these morphological modifications are unknown. The current study aims to elucidate the molecular modifications that lead to observed astrocyte structural changes in rats across cocaine abstinence using astrocyte-specific RiboTag and RNA-seq, as an unbiased, comprehensive approach to identify genes whose transcription or translation change within NAc astrocytes following cocaine self-administration and extended abstinence. Using this method, our data reveal cellular processes including cholesterol biosynthesis that are altered specifically by cocaine self-administration and abstinence, suggesting that astrocyte involvement in these processes is changed in cocaine-abstinent rats. Overall, the results of this study provide insight into astrocyte functional adaptations that occur due to cocaine exposure or during cocaine withdrawal, which may pinpoint further mechanisms that contribute to cocaine-seeking behavior.

The molecular diversity of hippocampal regions and strata at synaptic resolution revealed by integrated transcriptomic and proteomic profiling
The molecular diversity of neurons and their synapses underlies the different responses and plasticity profiles that drive all neural circuits and behavior. While the extent of this diversity has been partially revealed by transcriptomic and proteomic profiling, combined studies of neuronal transcripts and proteins are limited. Here, we used microdissection of mouse hippocampal subregions and CA1 strata and fluorescence-activated synaptosome sorting (FASS) to characterize the transcripts and proteins from different hippocampal neurons and their compartments with synaptic resolution. Parallel RNA-seq and LC-MS/MS of microdissections identified over 15,000 mRNA transcripts and 10,000 proteins, revealing thousands with local enrichment such as classes of glutamate receptors and voltage-gated potassium channels, myelin-associated molecules, and adhesion molecules. Synaptosome analysis further identified specific enrichment of molecules from collagen, ribosome, solute carrier, and receptor families at different synapses formed along CA1 neurons. By integrating mRNA and protein data, we defined clusters of co-regulated molecules such as adhesion and neurofilament proteins and transporter mRNAs, and found subsets of mRNA-protein pairs with strong correlation and anti-correlation in their abundance variation. Our findings comprise a rich resource on the molecular landscape of the hippocampus and its synapses that is accessible at syndive.org, and highlight the coordinated organization of transcripts and proteins between regions, neuronal compartments, and synapses.

Amyloid, Tau, and APOE in Alzheimer's Disease: Impact on White Matter Tracts
Alzheimer's disease (AD) is characterized by cognitive decline and memory loss due to the abnormal accumulation of amyloid-beta (Abeta) plaques and tau tangles in the brain; its onset and progression also depend on genetic factors such as the apolipoprotein E (APOE) genotype. Understanding how these factors affect the brain's neural pathways is important for early diagnostics and interventions. Tractometry is an advanced technique for 3D quantitative assessment of white matter tracts, localizing microstructural abnormalities in diseased populations in vivo. In this work, we applied BUAN (Bundle Analytics) tractometry to 3D diffusion MRI data from 730 participants in ADNI3 (phase 3 of the Alzheimer's Disease Neuroimaging Initiative; age range: 55-95 years, 349M/381F, 214 with mild cognitive impairment, 69 with AD, and 447 cognitively healthy controls). Using along-tract statistical analysis, we assessed the localized impact of amyloid, tau, and APOE genetic variants on the brain's neural pathways. BUAN quantifies microstructural properties of white matter tracts, supporting along-tract statistical analyses that identify factors associated with brain microstructure. We visualize the 3D profile of white matter tract associations with tau and amyloid burden in Alzheimer's disease; strong associations near the cortex may support models of disease propagation along neural pathways. Relative to the neutral genotype, APOE epsilon3/epsilon3, carriers of the AD-risk conferring APOE epsilon4 genotype show microstructural abnormalities, while carriers of the protective epsilon2 genotype also show subtle differences. Of all the microstructural metrics, mean diffusivity (MD) generally shows the strongest associations with AD pathology, followed by axial diffusivity (AxD) and radial diffusivity (RD), while fractional anisotropy (FA) is typically the least sensitive metric. Along-tract microstructural metrics are sensitive to tau and amyloid accumulation, showing the potential of diffusion MRI to track AD pathology and map its impact on neural pathways.

Aversion-induced drug taking and escape behavior involve similar nucleus accumbens core dopamine signaling signatures
Dopamine release in the nucleus accumbens core (NAcC) has long been associated with the promotion of motivated behavior. However, inhibited dopamine signaling can increase behavior in certain settings, such as during drug self-administration. While aversive environmental stimuli can reduce dopamine, it is unclear whether such stimuli reliably engage this mechanism in different contexts. Here we compared the physiological and behavioral responses to the same aversive stimulus in different designs to determine if there is uniformity in the manner that aversive stimuli are encoded and promote behavior. NAcC dopamine was measured using fiber photometry in male and female rats during cocaine self-administration sessions in which an acutely aversive 90 dB white noise was intermittently presented. In a separate group of rats, aversion-induced changes in dopamine were measured in an escape design in which operant responses terminated aversive white noise. Aversive white noise significantly reduced NAcC dopamine and increased cocaine self-administration in both male and female rats. The same relationship was observed in the escape design, in which white noise reduced dopamine and promoted escape attempts. In both designs, the magnitude of the dopamine reduction predicted behavioral performance. While prior research demonstrated that pharmacologically reduced dopamine signaling can promote intake, this report demonstrates that this physiological mechanism is naturally engaged by aversive environmental stimuli and generalizable to non-drug contexts. These findings illustrate a common physiological signature in response to aversion that may promote both adaptive and maladaptive behavior.

Tet2 loss suppress α-synuclein pathology by stimulating ciliogenesis
There are no approved treatments that slow Parkinsons disease (PD) progression and therefore it is important to identify novel pathogenic mechanisms that can be targeted. Loss of the epigenetic marker, Tet2 appears to have some beneficial effects in PD models, but the underlying mechanism of action is not well understood. We performed an unbiased transcriptomic analysis of cortical neurons isolated from patients with PD to identify dysregulated pathways and determine their potential contributions to the disease process. We discovered that genes associated with primary cilia, non-synaptic sensory and signaling organelles, are upregulated in both early and late PD patients. Enhancing ciliogenesis in primary cortical neurons via sonic hedgehog signaling suppressed the accumulation of alpha-synuclein pathology in vitro. Interestingly, deletion of Tet2 in mice also enhanced the expression of primary cilia and sonic hedgehog signaling genes and rescued the accumulation of alpha-synuclein pathology and dopamine neuron degeneration in vivo. Our findings demonstrate the crucial role of Tet2 loss in regulating ciliogenesis and potentially affecting the progression of PD pathology.

Sex-specific behavioral and thalamo-accumbal circuit adaptations after oxycodone abstinence.
Opioid use disorder is marked by a progressive change in the motivation to administer the drug even in the presence of negative consequences. After long periods of abstinence, the urge to return to taking the drug intensifies over time, known as incubation of craving. Conditioned responses to drug-related stimuli, can acquire motivational properties and exert control over motivated behaviors leading to relapse. Although, preclinical data suggest that the behavioral expression of opioid use is similar between male and female rodents, we do not have conclusive results on sex differences on craving and relapse across abstinence periods. Here, we investigated the effects of abstinence from oxycodone self-administration on neurotransmission in the paraventricular thalamus (PVT) to nucleus accumbens shell (NAcSh) pathway in male and female rats. Using optogenetics and ex vivo electrophysiology, we assessed synaptic strength and glutamate release probability in this pathway, as well as NAcSh medium spiny neurons (MSN) intrinsic excitability, in slices from rats which were subjected to either 1 (acute) or 14 (prolonged) days of forced abstinence after self-administration. Our results revealed no sex differences in oxycodone self-administration or somatic withdrawal symptoms following acute abstinence. However, we found a sex-specific enhancement in cue-induced relapse after prolonged, but not acute, abstinence from oxycodone self-administration, with females exhibiting higher relapse rates. Notably, prolonged abstinence led to similar increases in synaptic strength at PVT-NAcSh inputs compared to saline controls in both sexes, which was not observed after acute abstinence. Thus, prolonged abstinence results in a time-dependent increase in PVT-NAcSh synaptic strength and sex-specific effects on cue-induced relapse rates. These findings suggest that prolonged abstinence leads to significant synaptic changes, contributing to heightened relapse vulnerability, highlighting the need for targeted therapeutic strategies in opioid use disorder.

Model selection for spectral parameterization
Neurophysiological brain activity comprises rhythmic (periodic) and arrhythmic (aperiodic) signal elements, which are increasingly studied in relation to behavioral traits and clinical symptoms. Current methods for spectral parameterization of neural recordings rely on user-dependent parameter selection, which challenges the replicability and robustness of findings. Here, we introduce a principled approach to model selection, relying on Bayesian information criterion, for static and time-resolved spectral parameterization of neurophysiological data. We present extensive tests of the approach with ground-truth and empirical magnetoencephalography recordings. Data-driven model selection enhances both the specificity and sensitivity of spectral and spectrogram decompositions, even in non-stationary contexts. Overall, the proposed spectral decomposition with data-driven model selection minimizes the reliance on user expertise and subjective choices, enabling more robust, reproducible, and interpretable research findings.

Transmission of Mixed Convergent Signals at the Mouse Retinogeniculate Synapse
There are two broad modes of information transfer in the brain: the labeled line model, where neurons relay inputs they receive, and the mixed tuning model, where neurons transform and integrate different inputs. In the visual pathway, information transfer between retinal ganglion cells (RGCs) and the dorsal lateral geniculate nucleus (dLGN) neurons is primarily viewed as a labeled line. However, recent work in mice has demonstrated that different RGC types, encoding distinct visual features, can converge onto a dLGN neuron, raising the fundamental question of whether the dLGN transforms visual information. Using optogenetics we activated distinct RGC populations and assessed spiking output of dLGN neurons by in vivo recordings. We found that visual response properties of dLGN neurons driven by a specific RGC population largely matched properties of the activated RGCs. Furthermore, in vitro dual-opsin experiments demonstrate that strong functional convergence from distinct RGC types rarely occurs. Thus, retinogeniculate information transfer in mice largely adheres to a labeled line model.

Understanding the Sport Viewership Experience using Functional Near-Infrared Spectroscopy
Subjective evaluation of a sport event in real time is normally assessed using self-report measures, but neural indices of evaluative processing may provide new insights. The extent of evaluative processing of a sporting event at the neural level may depend on the degree of emotional investment by the viewer, as well as the key moment of the game play being observed. Those with high ego involvement might show more activation within evaluative processing nodes, and this pattern may be most pronounced during critical moments of game play. In the current study, we examined neural activations within the medial and lateral prefrontal cortex during game play as a function of ego-involvement, using video clips featuring key moments in a European league ice hockey game. A total of 343 participants were pre-screened to identify 20 high and low ego-involved individuals. These subgroups then viewed a game segment containing 12 key play moments, while undergoing neuroimaging using fNIRS. Findings indicated more engagement of the dmPFC throughout all key moments for high ego-involved participants, but particularly during critical game moments. Overall, findings suggest that neural indices of evaluative processing might contribute meaningfully to understanding when emotionally invested individuals are most engaged in an action sequence during a sporting event.

Head down tilt 15° increases cerebral perfusion before recanalization in acute ischemic stroke: a pre-clinical MRI study.
We investigated the therapeutic effect of head down positioning at -15{degrees} (head down tilt; HDT15) on cerebral collateral flow and infarct growth in a rat model of large vessel occlusion (LVO) stroke, using multimodal MRI. Twenty-eight Wistar rats were randomly assigned to HDT15 or flat position for 60 minutes, starting 30 minutes after occlusion of the middle cerebral artery, followed by reperfusion. The perfusion shift analysis, comparing post- versus pre-treatment voxel-level changes in time-to-peak perfusion maps, showed a significant increase in cerebral perfusion in the HDT15 group (common odds ratio 1.50; 95% CI 1.41-1.60; p < 0.0001), but not in the flat group (common odds ratio 0.97; 95% CI 0.92-1.03; p = 0.3503). Infarct growth at 24 hours was + 31.4% in the flat group (343 versus 250 mm3; 95% CI 2.4 to 165.1; p = 0.0447) and + 15.4% in the HDT15 group (224 versus 192 mm3; 95% CI -26.9 to 85.9; p = 0.2272). Our findings indicate that HDT15 acutely increases cerebral perfusion in LVO acute ischemic stroke and provides a tissue-saving effect before recanalization. Further research is needed to develop HDT15 as an emergency therapy to acutely increase collateral flow in ischemic stroke prior to recanalization therapy.

Individual alpha frequency tACS reduces functional connectivity across the default mode network
Objectives: Research on the influence of transcranial alternating current stimulation over alpha functional connectivity (FC) is scarce, and at the same time poses as a potential treatment for various diseases. This study aimed to investigate the effects of individualized alpha frequency tACS (IAF-tACS) on FC within the default mode network (DMN) in healthy individuals, particularly focusing on the precuneus (PCU) as a major hub within the network. Materials and Methods: 27 healthy participants were recruited, which underwent a 20-minute IAF-tACS session and three magnetoencephalography (MEG) recordings: two pre-stimulation and one post-stimulation. Participants were randomly assigned to either the stimulation or sham group. FC was evaluated through the corrected imaginary phase locking value (ci-PLV) and leakage corrected amplitude envelope correlation (AEC-c). Statistical analyses compared both Pre-Post FC ratio between groups through ratio t-tests and intragroup FC changes through repeated measures t-tests, with FDR correction applied to account for multiple comparisons. An additional analysis simulated the influence of the cortical folding on the effect of tACS over FC. Results: IAF-tACS significantly decreased AEC-c within the PCU and DMN in the stimulation group compared to the sham group, especially influencing antero-posterior links between hubs of the DMN. No significant changes were observed in ci-PLV connectivity metrics. Negative correlations were found between AEC-c FC changes and power alterations in posterior DMN areas, suggesting a complex interaction between cortical folding and electric field direction. Conclusions: Against our initial hypothesis, IAF-tACS reduced FC in the DMN, possibly due to phase disparities introduced by cortical gyrification. These findings suggest that tACS might modulate FC in a more complex manner than previously thought, highlighting the need for further research into the personalized application of neuromodulation techniques, as well as its potential therapeutic implications for conditions like Alzheimer's disease.

Multiscale heterogeneity of white matter morphometry in psychiatric disorders
Background: Interindividual variability in neurobiological and clinical characteristics in mental illness is often overlooked by classical group mean case control studies. Studies using normative modelling to infer person specific deviations of grey matter volume have indicated that group means are not representative of most individuals. The extent to which this variability is present in white matter morphometry, which is integral to brain function, remains unclear. Methods: We applied Warped Bayesian Linear Regression normative models to T1 weighted magnetic resonance imaging data and mapped interindividual variability in person specific white matter volume deviations in 1,294 cases (58% male) diagnosed with one of six disorders (attention-deficit/hyperactivity, autism, bipolar, major depressive, obsessive compulsive and schizophrenia) and 1,465 matched controls (54% male) recruited across 25 scan sites. We developed a framework to characterize deviation heterogeneity at multiple spatial scales, from individual voxels, through inter-regional connections, specific brain regions, and spatially extended brain networks. Results: The specific locations of white matter volume deviations were highly heterogeneous across participants, affecting the same voxel in fewer than 8% of individuals with the same diagnosis. For autism and schizophrenia, negative deviations (i.e., areas where volume is lower than normative expectations) aggregated into common tracts, regions and large scale networks in up to 35% of individuals. Conclusions: The prevalence of white matter volume deviations was lower than previously observed in grey matter, and the specific location of these deviations was highly heterogeneous when considering voxelwise spatial resolution. Evidence of aggregation within common pathways and networks was apparent in schizophrenia and autism but not other disorders.

Effects of Aging, Fitness, and Cerebrovascular Status on White Matter Microstructural Health
White matter (WM) microstructural health declines with increasing age, with evidence suggesting that improved cardiorespiratory fitness (CRF) may mitigate this decline. Specifically, higher fit older adults tend to show preserved WM microstructural integrity compared to their lower fit counterparts. However, the extent to which fitness and aging independently impact WM integrity across the adult lifespan is still an open question, as is the extent to which cerebrovascular health mediates these relationships. In a large sample (N = 125, aged 25-72), we assessed the impact of age and fitness on fractional anisotropy (FA, derived using diffusion weighted imaging, DWI) and probed the mediating role of cerebrovascular health (derived using diffuse optical tomography of the cerebral arterial pulse, pulse-DOT) in these relationships. After orthogonalizing age and fitness and computing a PCA on whole brain WM regions, we found several WM regions impacted by age that were independent from the regions impacted by fitness (hindbrain areas, including brainstem and cerebellar tracts), whereas other areas showed interactive effects of age and fitness (midline areas, including fornix and corpus callosum). Critically, cerebrovascular health mediated both relationships suggesting that vascular health plays a linking role between age, fitness, and brain health. Secondarily, we assessed potential sex differences in these relationships and found that, although females and males generally showed the same age-related FA declines, males exhibited somewhat steeper declines than females. Together, these results suggest that age and fitness impact specific WM regions and highlight the mediating role of cerebrovascular health in maintaining WM health across adulthood.

Evaluating permutation-based inference for partial least squares analysis of neuroimaging data
Partial least squares (PLS) is actively leveraged in neuroimaging work, typically to map latent variables (LVs) representing brain-behaviour associations. Canonically, LVs are considered statistically significant if they tend to capture more covariance than LVs derived from permuted data, with a Procrustes rotation applied to map each set of permuted LVs to the space defined by the originals, creating an 'apples to apples' comparison. Yet, it has not been established whether applying the rotation makes the permutation test more sensitive to the true LVs in a dataset, and it is unclear if significant LVs can be drawn from data with no meaningful between-feature covariance. Accordingly, we performed PLS analyses across a range of simulated datasets with known latent effects, observing that the Procrustes rotation systematically weakened the null distributions for the first LV. By extension, the first LV was nearly always significant, regardless of whether the effect was weak, undersampled, noisy, or simulated at all. But, if no rotation was applied, all possible LVs tended to be significant as we increased the sample size of UK BioBank datasets. Meanwhile, LV strength and stability metrics accurately tracked our confidence that effects were present in simulated data, and allowed for a more nuanced assessment of which LVs may be relevant in the UK BioBank. We end by presenting a list of considerations for researchers implementing PLS permutation testing, and by discussing promising alternative tests which may alleviate the concerns raised by our findings.

The influence of the head model on magnetoencephalography-derived functional connectivity fingerprinting
Functional connectivity (FC)-based neural fingerprinting is an approach that promises to distinguish subjects within a cohort on the basis of the patterns of statistical dependencies between time series recorded mostly if not always noninvasively, with electroencephalography (EEG), magnetoencephalography (MEG), or functional magnetic resonance imaging (fMRI). The message is that brain activity is what differentiates subjects, or in other words, what makes a neural fingerprint "unique". In EEG- and MEG-derived FC fingerprinting, the activity recorded at the sensors is projected back into cortical sources by means of an inverse model containing the shape of the head and its conductivity, and further averaged to obtain time series of regional activity, used to compute FC. In this study we investigated the role of the head model in fingerprinting. Through a set of experiments aimed to decouple recorded activity and head model for each subject, we found that the head model has a strong influence on the fingerprinting performance, according to two different sets of metrics.