Biology subjects

Anderson, M. C.

Publications and source records attributed to Anderson, M. C..

13 recordsLinked to original sources

bioRxiv2026

Amnesia Induced by Suppressing the Focus of Internal Attention

Our thoughts can recede as we direct attention to the external world. This experience may reflect the suppression of thoughts about past events, future worries, or stray ideas that could otherwise disrupt focus. Such thoughts may arise spontaneously from replay mechanisms supported by the episodic memory system; hence, sustaining external focus may require suppressing these systems to stop internal distraction. Here, periods of high external focus disrupted diverse episodic content activated near in time, inducing an 'amnesic shadow'. This shadow occurred for both novel content and already formed memories and exhibited key markers of active suppression: forgetting beyond expectations from time alone, which generalised to an alternative reminder. External attention therefore automatically engages an active suppression mechanism that appears to broadly inhibit cognitive systems supporting the emergence of distracting thoughts. The findings raise the possibility that people may naturally gravitate toward activities demanding external attention, unwittingly, to regulate unwanted thoughts.

neuroscience↗

bioRxiv2024

Dissecting the functional heterogeneity of glutamatergic synapses with high-throughput optical physiology

Fluorescent reporters for glutamate release and postsynaptic Ca2+ signaling are essential tools for quantifying synapse functional heterogeneity across neurons and circuits. However, leveraging these probes for neuroscience requires scalable experimental frameworks. Here, we devised a high-throughput approach to efficiently collect and analyze hundreds of optical recordings of glutaamate release activity at presynaptic boutons in cultured rat hippocampal neurons. Boutons exhibited remarkable functional heterogeneity and could be separated into multiple functional classes based on their iGluSnFR3 responses to single action potentials, paired stimuli, and synaptic parameters derived from mean-variance analysis. Finally, we developed a novel all-optical assay of pre- and postsynaptic glutamatergic synapse function. We deployed iGluSnFR3 with a red-shifted, postsynaptically-targeted Ca2+ sensor, enabling direct imaging and analysis of NMDA receptor-mediated synaptic transmission at large numbers of dendritic spines. This work enables direct observation of the flow of information at single synapses and should speed detailed investigations of synaptic functional heterogeneity.

neuroscience↗

bioRxiv2024

Large donor CRISPR for whole-CDS replacement of cell adhesion molecule LRRTM2

The cell adhesion molecule LRRTM2 is crucial for synapse development and function. However, our understanding of its endogenous trafficking has been limited due to difficulties in manipulating its coding sequence (CDS) using standard genome editing techniques. We instead replaced the whole LRRTM2 CDS by adapting the recent CRISPR method Targeted Knock-in using Two Guides (TKIT), enabling complete control of LRRTM2. In primary rat hippocampal cultures, N-terminally tagged, endogenous LRRTM2 was found in 80% of synapses, and synaptic LRRTM2 content correlated with PSD-95 and AMPAR levels. LRRTM2 was also enriched with AMPARs outside synapses, demonstrating the sensitivity of this method to detect relevant new biology. Finally, we leveraged total genomic control to increase the synaptic levels of LRRTM2 via simultaneous mutation of its C-terminal domain, which did not correspondingly increase AMPAR enrichment. The coding region of thousands of genes span lengths suitable for whole-CDS replacement, suggesting this simple approach will enable straightforward structure-function analysis in diverse cellular systems.

neuroscience↗

bioRxiv2024

Loss of postsynaptic NMDARs drives nanoscale reorganization of Munc13-1 and PSD-95

Nanoscale protein organization within the active zone (AZ) and post-synaptic density (PSD) influences synaptic transmission. Nanoclusters of presynaptic Munc13-1 are associated with readily releasable pool size and neurotransmitter vesicle priming, while postsynaptic PSD-95 nanoclusters coordinate glutamate receptors across from release sites to control their opening probability. Nanocluster number, size, and protein density vary between synapse types and with development and plasticity, supporting a wide range of functional states at the synapse. Whether or how the receptors themselves control this critical architecture remains unclear. One prominent PSD molecular complex is the NMDA receptor (NMDAR). NMDARs coordinate several modes of signaling within synapses, giving them the potential to influence synaptic organization through direct protein interactions or through signaling. We found that loss of NMDARs results in larger synapses that contain smaller, denser, and more numerous PSD-95 nanoclusters. Intriguingly, NMDAR loss also generates retrograde reorganization of the active zone, resulting in denser, more numerous Munc13-1 nanoclusters, more of which are aligned with PSD-95 nanoclusters. Together, these changes to synaptic nanostructure predict stronger AMPA receptor-mediated transmission in the absence of NMDARs. Notably, while prolonged antagonism of NMDAR activity increases Munc13-1 density within nanoclusters, it does not fully recapitulate these trans-synaptic effects. Thus, our results confirm that NMDARs play an important role in maintaining pre- and postsynaptic nanostructure and suggest that both decreased NMDAR expression and suppressed NMDAR activity may exert distinct effects on synaptic function, yet through unique architectural mechanisms. Significance StatementSynaptic transmission is shaped by the trans-synaptic coordination of molecular ensembles required for neurotransmitter release and receptor retention, but how receptors themselves influence this critical architecture remains unclear. Using state-of-the-art super-resolution microscopy, we report that loss of NMDA receptors from excitatory synapses alters both pre- and postsynaptic nano-organizational features. Notably, pharmacological antagonism of NMDA receptors also alters presynaptic features, but without fully mimicking effects of the knockout. This suggests that both NMDA receptor activity and presence at the synapse exert retrograde influence on active zone organization. Because numerous disease and activity states decrease expression or function of NMDA receptors, our results suggest that distinct nanostructural states contribute to the unique functional status of synapses in these disorders.

neuroscience↗

bioRxiv2023

Trans-synaptic molecular context of NMDA receptor nanodomains

Tight coordination of the spatial relationships between protein complexes is required for cellular function. In neuronal synapses, many proteins responsible for neurotransmission organize into subsynaptic nanoclusters whose trans-cellular alignment modulates synaptic signal propagation. However, the spatial relationships between these proteins and NMDA receptors (NMDARs), which are required for learning and memory, remain undefined. Here, we mapped the relationship of key NMDAR subunits to reference proteins in the active zone and postsynaptic density using multiplexed super-resolution DNA-PAINT microscopy. GluN2A and GluN2B subunits formed nanoclusters with diverse configurations that, surprisingly, were not localized near presynaptic vesicle release sites marked by Munc13-1. Despite this, we found a subset of release sites was enriched with NMDARs, and modeling of glutamate release and receptor activation in measured synapses indicated this nanotopography promotes NMDAR activation. This subset of release sites was internally denser with Munc13-1, aligned with abundant PSD-95, and associated closely with specific NMDAR nanodomains. Further, NMDAR activation drove rapid reorganization of this release site/receptor relationship, suggesting a structural mechanism for tuning NMDAR-mediated synaptic transmission. This work reveals a new principle regulating NMDAR signaling and suggests that synaptic functional architecture depends on the assembly of and trans-cellular spatial relationships between multiprotein nanodomains.

neuroscience↗

bioRxiv2023

Memory control deficits in the sleep-deprived human brain

Sleep disturbances are associated with intrusive memories, but the neurocognitive mechanisms underpinning this relationship are poorly understood. Here, we show that an absence of sleep disrupts prefrontal inhibition of memory retrieval, and that the overnight restoration of this inhibitory mechanism is predicted by time spent in rapid eye movement (REM) sleep. The functional impairments arising from sleep loss are linked to a behavioural deficit in the ability to suppress unwanted memories, and coincide with a deterioration of deliberate patterns of self-generated thought. We conclude that sleep deprivation gives rise to intrusive memories via the disruption of neural circuits governing mnemonic inhibitory control, which may rely on REM sleep.

neuroscience↗

bioRxiv2023

Distinct SAP102 and PSD-95 nano-organization defines multiple types of synaptic scaffold protein domains at single synapses

The MAGUK family of scaffold proteins plays a central role in maintaining and modulating synaptic signaling, providing a framework to retain and position receptors, signaling molecules, and other synaptic components. Of these scaffold proteins, SAP102 and PSD-95 are essential for synaptic function at distinct developmental timepoints and perform overlapping as well as unique roles. While their similar structures allow for common binding partners, SAP102 is expressed earlier in synapse development and is required for synaptogenesis, whereas PSD-95 expression peaks later in development and is associated with synapse maturation. PSD-95 and other key synaptic proteins organize into subsynaptic nanodomains that have a significant impact on synaptic transmission, but the nanoscale organization of SAP102 is unknown. How SAP102 is organized within the synapse, and how it relates spatially to PSD-95 on a nanometer scale, could impact how SAP102 clusters synaptic proteins and underlie its ability to perform its unique functions. Here we used DNA-PAINT super-resolution microscopy to measure SAP102 nano-organization and its spatial relationship to PSD-95 at individual synapses. We found that like PSD-95, SAP102 accumulates in high-density subsynaptic nanoclusters. However, SAP102 nanoclusters were smaller and denser than PSD-95 nanoclusters across development. Additionally, only a subset of SAP102 nanoclusters co-organized with PSD-95, revealing that within individual synapses there are nanodomains that contain either one or both proteins. This organization into both shared and distinct subsynaptic nanodomains may underlie the ability of SAP102 and PSD-95 to perform both common and unique synaptic functions. Significance statementSAP102 and PSD-95 are two key members of the MAGUK family of synaptic scaffold proteins that are critical for synapse development, maintenance, and modification during plasticity. Because PSD-95 has a highly complex subsynaptic nanostructure that impacts synaptic function, we asked if SAP102 is similarly organized into nanoclusters at individual synapses and how it relates to PSD-95 within synapses. We found that SAP102 forms subsynaptic nanoclusters with unique properties, and that within individual synapses proteins both concentrate into overlapping nanodomains, as well as form MAGUK-specific nanodomains. This demonstrates that organization of synaptic proteins into nanoclusters is likely to be maintained within the family of MAGUK proteins and reveals potential mechanism for specializing functions within individual synapses based on scaffold protein nanodomains.

neuroscience↗

bioRxiv2022

Reduced Hippocampal-Cortical Connectivity During Memory Suppression Predicts the Ability to Forget Unwanted Memories

The ability to suppress unwelcome memories is important for productivity and well-being. Successful memory suppression is associated with hippocampal deactivations and a concomitant disruption of this regions functionality. Much of the previous neuroimaging literature exploring such suppression-related hippocampal modulations has focused on the regions negative coupling with the prefrontal cortex. In contrast, task-based changes in functional connectivity between the hippocampus and other brain regions have remained relatively underexplored. Here, we utilize psychophysiological interactions and seed connectome-based predictive modeling (seed-CPM) to investigate the relationship between the hippocampus and the rest of the brain as 134 participants attempted to suppress unwanted memories during the Think/No-Think task. The results show that during retrieval suppression, the right hippocampus exhibited decreased functional connectivity with visual cortical areas (bilateral intracalcarine cortex, right cuneal cortex, left lingual gyrus, right supracalcarine cortex, right occipital pole), left nucleus accumbens and the brain-stem that predicted superior forgetting of unwanted memories on later memory tests. Validation tests verified that prediction performance was not an artifact of head motion or prediction method and that the negative features remained consistent across different brain parcellations. These findings suggest that systemic memory suppression involves more than the modulation of hippocampal activity--it alters functional connectivity patterns between the hippocampus and visual cortex, leading to successful forgetting.

neuroscience↗

bioRxiv2021

Dopamine modulates adaptive forgetting in medial prefrontal cortex

Active forgetting occurs in many species, but how the mechanisms that control behavior contribute to determining which memories are forgotten is still unknown. We previously found that when rats need to retrieve particular memories to guide exploration, it reduces later retention of other memories encoded in that environment. As with humans, this retrieval-induced forgetting relies on prefrontal control processes. The dopaminergic input to the prefrontal cortex is important for executive functions and cognitive flexibility. We found that, in a similar way, prefrontal dopamine signaling through D1 receptors is required for retrieval-induced forgetting in rats. Blockade of medial prefrontal cortex D1 receptors as animals encountered a familiar object impaired forgetting of the memory of a competing object in a subsequent long-term memory test. Inactivation of the ventral tegmental area produced the same pattern of behavior, a pattern that could be reversed by concomitant activation of prefrontal D1 receptors. We observed a bidirectional modulation of retrieval-induced forgetting by agonists and antagonists of D1 receptors in the medial prefrontal cortex. These findings establish the essential role of prefrontal dopamine in the active forgetting of competing memories, contributing to the shaping of retention in response to an organisms behavioral goals.

animal behavior and cognition↗

bioRxiv2020

Dynamic targeting enables domain-general inhibitory control over action and thought by the prefrontal cortex.

Successful self-control requires the ability to stop unwanted actions or thoughts. Stopping is regarded as a central function of inhibitory control, a mechanism enabling the suppression of diverse mental content, and strongly associated with the prefrontal cortex. A domain-general inhibitory control capacity, however, would require the region or regions implementing it to dynamically shift top-down inhibitory connectivity to diverse target regions in the brain. Here we show that stopping unwanted thoughts and stopping unwanted actions engage common regions in the right anterior dorsolateral and right ventrolateral prefrontal cortex, and that both areas exhibit this dynamic targeting capacity. Within each region, pattern classifiers trained to distinguish stopping actions from making actions also could identify when people were suppressing their thoughts (and vice versa) and could predict which people successfully forgot thoughts after inhibition. Effective connectivity analysis revealed that both regions contributed to action and thought stopping, by dynamically shifting inhibitory connectivity to motor area M1 or to the hippocampus, depending on the goal, suppressing task-specific activity in those regions. These findings support the existence of a domain-general inhibitory control mechanism that contributes to self-control and establish dynamic inhibitory targeting as a key mechanism enabling these abilities.

neuroscience↗

bioRxiv2020

The ascorbate-deficient guinea pig model of shigellosis allows the study of the entire Shigella life cycle

Shigella spp. are the causative agents of bacillary dysentery or shigellosis, mainly in children living in developing countries. The study of Shigella entire life cycle in vivo and the evaluation of vaccine candidates protection efficacy have been hampered by the lack of a suitable animal model of infection (1). None of the ones evaluated so far (mouse, rabbit, guinea pig) allows to recapitulate shigellosis symptoms upon Shigella oral challenge. Historical reports suggest that dysentery and scurvy are both metabolic diseases associated with ascorbate-deficiency. Mammals which are susceptible to Shigella infection (humans, non-human primates and guinea pigs) are the lonely ones which are unable to synthesize ascorbate. We optimized a low-ascorbate diet to induce moderate ascorbate-deficiency but not scurvy in guinea pigs (Ascplasma conc.=1.6 M vs 36 M with optimal ascorbate supply). We demonstrated that moderate ascorbate-deficiency increases shigellosis severity during extended period of time (up to 48h) with all strains tested (Shigella flexneri 5a and 2a, Shigella sonnei). At late time-points, a massive influx of neutrophils was observed both within the disrupted colonic mucosa and in the luminal compartment, although Shigella remains able to disseminate deep into the organ to reach the sub-mucosal layer and the bloodstream. This new model of shigellosis opens new doors for the study both of Shigella infection strategy and innate and adaptive immune responses to Shigella infection. It may be also of a great interest to study the virulence of other pathogen for which no suitable animal model of infection is available (Vibrio cholerae, Yersinia pestis, Mycobacterium tuberculosis or Campylobacter jejuni, among others). SignificanceThe study of Shigella virulence cycle in vivo has been hampered by the lack of a suitable animal model, which would allow the colonic mucosa infection upon oral challenge. Based on historical reports and physiological aspects, it was suggested that ascorbate-deficiency may stand as a new dysentery risk-factor. To test this hypothesis, we set up a new ascorbate-deficient guinea pig model and demonstrated for the first time that the Shigella infectious process occurred for extended period of time (up to 48h) and demonstrated that shigellosis severity was higher in ascorbate-deficient animal. Ascorbate-deficient guinea pig model of infection may be used to assess the virulence of other pathogens for which no suitable animal model of infection is still lacking.

microbiology↗

bioRxiv2020

IlvY is an important regulator of Shigella infection in vitro and in vivo

Shigellosis results from oral ingestion of the Gram-negative bacteria Shigella, and symptoms include severe diarrhea and dysentery. In the absence of vaccines, small molecule antibacterial drugs have provided treatment options for shigellosis. However, Shigella drug resistance is rapidly emerging, and Shigella strains with resistance to both third-generation cephalosporins and azithromycin have been identified in Asia. A re-conceptualization is needed regarding the development of therapeutics that target bacterial pathogens in order to reduce resistance development and alteration of gut microbiota, which is depleted upon treatment with wide spectrum antibiotics, thereby increasing susceptibility to subsequent enteric infections. A more organism-specific approach is to develop agents targeting virulence factors such as toxins, adhesins, invasins, quorum sensing, and protein secretion systems. For Shigella, there is interest in targeting transcription factors essential for Shigella infection in vivo rather than specific effectors. Here we describe the importance of the Shigella transcription factor IlvY in Shigella virulence in vitro and in vivo. This work included the development of a novel, oral mouse model of Shigella infection with wild-type adult mice. Unlike previous models, mice do not require antibiotic pretreatment or diet modifications. This mouse model was used to demonstrate the importance of IlvY for Shigella in vivo survival and that deletion of ilvY impacts host responses to infection. These results illustrate that IlvY is a potential therapeutic target for the treatment of shigellosis. In addition, the novel mouse model provides an exciting new opportunity to investigate therapeutic efficacy against Shigella infection and host responses to infection.

microbiology↗

bioRxiv2019

Losing Control: Sleep Deprivation Impairs the Suppression of Unwanted Thoughts

Unwanted memories often enter conscious awareness when we confront reminders. People vary widely in their talents at suppressing such memory intrusions; however, the factors that govern suppression ability are poorly understood. We tested the hypothesis that successful memory control requires sleep. Following overnight sleep or total sleep deprivation, participants attempted to suppress intrusions of emotionally negative and neutral scenes when confronted with reminders. The sleep-deprived group experienced significantly more intrusions (unsuccessful suppressions) than the sleep group. Deficient control over intrusive thoughts had consequences: whereas in rested participants suppression reduced behavioural and psychophysiological indices of negative affect for aversive memories, it had no such salutary effect for sleep-deprived participants. Our findings raise the possibility that sleep deprivation disrupts prefrontal control over medial temporal lobe structures that support memory and emotion. These data point to an important role of sleep disturbance in maintaining and exacerbating psychiatric conditions characterised by persistent, unwanted thoughts.

neuroscience↗