Biology subjects

Muir, J.

Publications and source records attributed to Muir, J..

9 recordsLinked to original sources

bioRxiv2025

Whole brain dimensional approach identifies shared and sex-specific networks of stress susceptibility in male and female mice.

Stress is a major risk factor for depression and anxiety, two highly comorbid disorders with sex differences in symptom presentation and prevalence. Accumulating evidence on the chronic variable stress (CVS) mouse model has revealed that stress susceptibility is sex-specific, as females require less stress exposure (6 days) compared to males (21-28 days) to develop comparable adaptations in depressive- and anxiety-like behaviors. However, the neuroanatomical changes associated with stress susceptibility remain unclear in each sex. Given this differential susceptibility, elucidating these mechanisms requires a phenotype-matched approach in which stress duration is titrated in a sex-specific manner to induce comparable behavioral adaptations. Here, we used a multi-variate brain-behavior and connectomic analysis to examine signatures of stress susceptibility in female and male mice. Using structural magnetic resonance imaging (MRI), we investigate whole-brain neuroanatomical changes associated with behavioral susceptibility within each sex. We then examined the structural connectome underlying neuroanatomical changes associated with behavioral susceptibility within each sex, and putative molecular basis for behaviorally-relevant changes using spatial gene expression analyses. CVS induced significant neuroanatomical changes in regions commonly implicated in anxiety- and depressive-like phenotypes in both sexes (e.g. nucleus accumbens and hippocampus); however qualitative differences between sexes in the direction of change were observed. In addition to these changes, in females stress-induced neuroanatomical changes were associated with both depressive- and anxiety-like behavior, whereas in males we observed two orthogonal dimensions of neuroanatomical changes associated with anxiety-like behavior or social preference. The connectomic topology underlying these brain-behavior dimensions revealed the cortical hub regions for females and subcortical hub regions for males. In females, neuroanatomical changes were associated with genes enriched for protein localization to the cell surface, suggesting alterations in cholinergic signaling By implementing a phenotype-matched CVS protocol, our findings indicate that the neuroanatomical signature of stress susceptibility encompasses similar brain regions across both sexes, however the direction of change, association to behavior and connectomic properties may differ in each sex.

neuroscience↗

bioRxiv2025

D3 dopamine receptors implicate a subtype of medium spiny neuron in the aversive effects of antipsychotic medications

Second generation antipsychotics (SGAs) are widely used clinical tools; yet, they often cause negative side effects and take weeks to become effective, leading to poor patient compliance. The effect/side effect profile of individual SGAs is highly variable, and the mechanisms that underlie this variability are not well understood. Here, we identify a role of type 3 dopamine receptor (D3R) neurons in the Nucleus Accumbens (NAc) that mimics the aversive effects of quetiapine. Using single-nucleus RNA sequencing, we show that D3R is expressed in a subpopulation of D1R neurons and defines a distinct NAc cell type. We found that both clozapine and quetiapine cause acute conditioned place aversion in mice, but aversion subsides only after 21 days of treatment with quetiapine, a drug characterized as an arrestin-biased agonist at D3R. We provide evidence at both the cellular and population level that quetiapine inhibits D3R-expressing neurons in the lateral shell (LatSh) of the NAc. We also demonstrate that local injection of quetiapine into LatSh NAc is sufficient to cause place aversion. Selective optogenetic inhibition of D3R-neurons in the LatSh produces real time place aversion in mice, correlating this cell type to the aversive effects of quetiapine. These findings suggest a cell-type-specific mechanism underlying quetiapine-induced aversion and its potential attenuation with chronic treatment, offering insight into the cell types and circuitry that shape the quetiapine side effect profile.

neuroscience↗

bioRxiv2025

High-Speed Neural Imaging with Multiplexed Miniature Two-Photon Microscopy (M-MINI2P)

Head-mounted miniaturized two-photon microscopes are powerful tools to record neural activity with cellular resolution deep in the mouse brain during unrestrained, free-moving behavior. Two-photon microscopy, however, is traditionally limited in imaging frame rate due to the necessity of raster scanning the laser excitation spot over a large field-of-view (FOV). Here, we present two multiplexed miniature two-photon microscopes (M-MINI2Ps) to increase the imaging frame rate while preserving the spatial resolution. Two different FOVs are imaged simultaneously and then demixed temporally or computationally. We demonstrate large-scale (500x500 m2 FOV) multiplane calcium imaging in visual cortex and prefrontal cortex in freely moving mice for spontaneous activity and auditory stimulus evoked responses. Furthermore, the increased speed of M-MINI2Ps also enables two-photon voltage imaging at 400 Hz over a 380x150 m2 FOV in freely moving mice. M-MINI2Ps have compact footprints and are compatible with the open-source MINI2P. M-MINI2Ps, together with their design principles, allow the capture of faster physiological dynamics and population recordings over a greater volume than currently possible in freely moving mice, and will be a powerful tool in systems neuroscience.

neuroscience↗

bioRxiv2024

Uncertainty gates redundancy in reward integration in prefrontal-cortical and ventral-hippocampal nucleus accumbens inputs to tune engagement

The NAc, a highly integrative brain region controlling motivated behavior, is thought to receive distinct information from various glutamatergic inputs yet strong evidence of functional specialization of inputs is lacking. While circuit neuroscience commonly seeks specific functions for specific circuits, redundancy can be highly adaptive and is a critical motif in circuit organization. Using dual-site fiber photometry in an operant reward task, we simultaneously recorded from two NAc glutamatergic afferents to assess circuit specialization. We identify a common neural motif that integrates reward history in medial prefrontal cortex (mPFC) and ventral hippocampus (vHip) inputs to NAc. Then, by systematically degrading task complexity, dissociating reward from choice and action, we identify key circuit-specificity in the behavioral conditions that recruit encoding. While mPFC-NAc invariantly encodes reward, vHip-NAc encoding is uniquely anchored to loss. Ultimately, using optogenetic stimulation we demonstrate that both inputs co-operatively modulate task engagement. We illustrate how similar encoding, with differential gating by behavioral state, supports state-sensitive tuning of reward-motivated behavior.

neuroscience↗

bioRxiv2023

Prefrontal Cortex Astroglia Modulate Anhedonia-like Behavior

Reductions of astroglia expressing glial fibrillary acidic protein (GFAP) are consistently found in the prefrontal cortex (PFC) of patients with depression and in rodent chronic stress models. Here, we examine the consequences of PFC GFAP+ cell depletion and cell activity enhancement on depressive-like behaviors in rodents. Using viral expression of diphtheria toxin receptor in PFC GFAP+ cells, which allows experimental depletion of these cells following diphtheria toxin administration, we demonstrated that PFC GFAP+ cell depletion induced anhedonia-like behavior within 2 days and lasting up to 8 days, but no anxiety-like deficits. Conversely, activating PFC GFAP+ cell activity for 3 weeks using designer receptor exclusively activated by designer drugs (DREADDs) reversed chronic restraint stress-induced anhedonia-like deficits, but not anxiety-like deficits. Our results highlight a critical role of cortical astroglia in the development of anhedonia and further support the idea of targeting astroglia for the treatment of depression.

neuroscience↗

bioRxiv2022

Dietary fibre controls blood pressure and cardiovascular risk by lowering large intestinal pH and activating the proton-sensing receptor GPR65

High blood pressure (BP) is the most common cause of death globally, due to increasing the risk of cardiovascular diseases. Dietary fiber regulates BP through gut microbial production of acidic metabolites known as short-chain fatty acids (SCFAs). The specific mechanisms of how SCFAs regulate BP are still emerging. In a phenome-wide association study, we identified that the proton-sensing G-protein-coupled receptor GPR65 gene is associated with hypertension and its associated end-organ damage phenotypes. We hypothesized that acidic metabolites produced from the gut microbiota may activate GPR65, thus conferring BP regulating effects. We found that dietary fiber levels determined the luminal and interstitial tissue pH in the large intestine through production of SCFAs by the gut microbiota. We identified that low pH produced by high fiber intake, acting via GPR65 signaling, increased cAMP production and phosphorylation of CREB, and restricted the production of hypertension-promoting inflammatory cytokines by CD8+ T cells. Gpr65-/- mice spontaneously developed higher BP, cardiac and renal hypertrophy and fibrosis. We showed that the benefits of a diet high in fiber, which prevented hypertension and associated end-organ damage, were decreased in Gpr65-/- mice. Finally, adoptive transfers revealed that GPR65 deficiency in CD8+ T cells causally explained this phenotype. In conclusion, we showed that pH sensing by GPR65 in CD8+ T cells mediates much of the cardiovascular benefits of dietary fiber. pH sensing represents a novel gene-by-environment interaction of gut microbiota-to-host biological effects and may form the basis for new therapeutic strategies for hypertension.

molecular biology↗

bioRxiv2022

Higher habitual FODMAP intake is associated with lower body mass index, lower insulin resistance and higher short-chain fatty acid-producing microbiota in people with prediabetes

Aims/hypothesisThe quantity and quality of FODMAPs can alter the relative abundance of gut microbiota with metabolic consequences although similar data are lacking in people with prediabetes. We investigated associations between habitual FODMAP contents, gut microbiota and glucose/insulin responses in subjects with prediabetes. MethodsIn this prospective cross-sectional study, ninety-eight subjects with impaired glucose tolerance (IGT) (mean age: 57{+/-}7 years, 43 % men) had assessment of body composition, 6-point oral glucose tolerance tests (OGTT), Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) and 3-day dietary intake. We analysed faecal samples in a sub-group of 20 subjects with IGT and 10 subjects with normal glucose tolerance by 16S rRNA microbiome analysis. ResultsObese subjects with IGT had the lowest daily FODMAP intake compared with their non-overweight and non-obese counterparts (5.7 (3.9-7.9) vs 7.1 (5.0-11.3) vs 9.9 (4.1-22.4) g/day, p=0.024) despite having similar total daily energy intake. Total content of FODMAPs was negatively correlated with body fat. After adjustment for age and gender, total FODMAPs were negatively associated with BMI and HOMA-IR. This remained significant after adjustment for macronutrients and physical activity (p=0.032 and p=0.036 respectively). FODMAP contents were strongly associated with short-chain fatty acid (SCFA)-producing bacteria, such as Lactobacillus (p=0.011), Akkermansia muciniphila (p=0.012), and Bifidobacterium longum (p=0.010), the abundance of which were negatively correlated with 2-hr plasma glucose (r = -0.524, p =0.003). ConclusionIn individuals with IGT, higher habitual FODMAP intake was associated with lower body fat and insulin resistance and increased abundance of SCFA-producing bacteria, calling for interventional studies to evaluate the effects of FODMAP intake in prediabetes.

microbiology↗

bioRxiv2022

Sexually dimorphic neural encoding of threat discrimination in nucleus accumbens afferents drives suppression of reward behavior

Learning to predict threat is essential but equally important yet often overlooked is learning about the absence of threat. Interrogating neural activity in two nucleus accumbens afferents in male and female mice during aversive and neutral cues reveals sex-specific encoding of cue discrimination and cuemediated suppression of reward behavior. Sexual dimorphisms in neural bases of threat discrimination may reflect sex differences in behavioral strategy relevant to differential psychiatric risk.

neuroscience↗

bioRxiv2020

Adaptive synaptic plasticity maintains CRH neuron output during chronic glucocorticoid exposure

An increase in circulating glucocorticoids (CORT) is an essential part of the response to stress. Sustained elevations of CORT, however, have dramatic consequences on behavior, endocrine systems and peripheral organs. Critically, they dampen the endocrine response to acute challenges and decrease intrinsic excitability of corticotropin-releasing hormone neurons in the paraventricular nucleus (CRHPVN), suggesting key circuits may be less responsive to stress. Here, we make the surprising discovery that CRHPVN neurons harness a form of adaptive synaptic scaling to escape the persistent negative feedback pressure from CORT and maintain stable output in vivo. Specifically, there is an increase in glutamatergic drive to these cells that is mediated by a postsynaptic, multiplicative increase in synaptic strength. These findings suggest that dysfunctions associated with chronic stress may not be due to the primary actions of CORT, but instead reflect the emergence of synaptic adaptations as networks seek to re-establish intrinsic activity setpoints.

neuroscience↗