Biology subjects

Holt, L. M.

Publications and source records attributed to Holt, L. M..

10 recordsLinked to original sources

bioRxiv2026

A shared transcriptional network in the nucleus accumbens supports resilience to chronic stress across sex.

Although chronic stress increases the risk for depression, only a subset of exposed individuals develop psychiatric illness. The biological mechanisms that protect against depression remain incompletely understood, particularly at the molecular level. Here, we identify a transcriptional network in the nucleus accumbens (NAc), a central brain reward region, that supports stress resilience in both sexes and demonstrate the causal contribution of key hub genes. Using chronic social defeat stress, RNA-seq, and co-expression network analysis, we find sex-specific but overlapping gene modules linked to resilience, anchored by shared hub genes embedded within a common network architecture. Overexpression of these hub genes in stress-naive mice confers stress protection and induces a transcriptional state that is discrete from both susceptible and resilient profiles. These findings position resilience as a structured and targetable molecular phenotype and provide a basis for investigating sex-informed mechanisms of stress adaptation.

neuroscience↗

bioRxiv2025

Astrocytic CREB regulates transcriptional, neuronal, and behavioral responses to cocaine

Drug addiction is characterized by neuronal adaptations that support a shift from goal-directed behaviors to habitual, compulsive drug-seeking with persistent effects on cognition and decision-making. Emerging evidence increasingly indicates that astrocytes are also involved in nervous system disorders, including addiction, but the cocaine-induced astrocyte-specific transcriptome has not yet been investigated. We utilized whole cell sorting of astrocytes, RNA-sequencing, and bioinformatic approaches to characterize the astrocyte transcriptome in the nucleus accumbens (NAc), a key brain region involved in reward-processing, following cocaine self-administration, prolonged abstinence, and "relapse" in male mice. We found that astrocytes exhibit robust and contextually-specific transcriptional signatures that converge strongly with human cocaine use disorder. Bioinformatic analysis revealed CREB as a highly ranked predicted upstream regulator of cocaine-induced transcriptional regulation in NAc astrocytes, and CUT&RUN-sequencing mapped increased CREB binding across the astrocyte genome in response to cocaine. Viral-mediated manipulation of CREB activity selectively in NAc astrocytes, in combination with several measures of addiction-related behaviors including conditioned place preference and self-administration, revealed that astrocytic CREB increases the rewarding and reinforcing properties of cocaine. This effect is sex-specific, with no change in astrocytic CREB activity or CPP found in females. Subsequent experiments identify potential molecular mechanisms of astrocytic CREBs influence through modulating astrocytic Ca2+ signaling in response to cocaine. Finally, we show that astrocytic CREB selectively modulates D1-type medium spiny neurons in NAc to control cocaine-related behaviors. Together, these data demonstrate that the astrocyte transcriptome responds robustly to cocaine and that CREB mediates cocaines effects on gene expression in astrocytes, with consequent effects on neuronal activity and rewarding responses to the drug.

neuroscience↗

bioRxiv2024

Cell-Type-Specific Regulation of Cocaine Reward by the E2F3a Transcription Factor in Nucleus Accumbens

The development of drug addiction is characterized by molecular changes in brain reward regions that lead to the transition from recreational to compulsive drug use. These neurobiological processes in brain reward regions, such as the nucleus accumbens (NAc), are orchestrated in large part by transcriptional regulation. Our group recently identified the transcription factor E2F3a as a novel regulator of cocaines rewarding effects and gene expression regulation in the NAc of male mice. Despite this progress, no information is available about the role of E2F3a in regulating cocaine reward at the sex- and cell-specific levels. Here, we used male and female mice expressing Cre-recombinase in either D1- or D2-type medium spiny neurons (MSNs) combined with viral-mediated gene transfer to bidirectionally control levels of E2F3a in a cell-type-specific manner in the NAc during conditioned place preference (CPP) to cocaine. Our findings show that selective overexpression of E2F3a in D1-MSNs increased cocaine CPP in both male and female mice, whereas opposite effects were observed under knockdown conditions. In contrast, equivalent E2F3a manipulations in D2-MSNs had no significant effects. To further explore the role of E2F3a in sophisticated operant and motivated behaviors, we performed viral manipulations of all NAc neurons in combination with cocaine self-administration and behavioral economics procedures in rats and demonstrated that E2F3a regulates sensitivity aspects of cocaine seeking and taking. These results confirm E2F3a as a central substrate of cocaine reward and demonstrate that this effect is mediated in D1-MSNs, thereby providing increased knowledge of cocaine action at the transcriptional level.

neuroscience↗

bioRxiv2024

Transcriptional characterization of cocaine withdrawal versus extinction within nucleus accumbens

Substance use disorder is characterized by a maladaptive imbalance wherein drug seeking persists despite negative consequences or drug unavailability. This imbalance correlates with neurobiological alterations some of which are amplified during forced abstinence, thereby compromising the capacity of extinction-based approaches to prevent relapse. Cocaine use disorder (CUD) exemplifies this phenomenon in which neurobiological modifications hijack brain reward regions such as the nucleus accumbens (NAc) to manifest craving and withdrawal-like symptoms. While increasing evidence links transcriptional changes in the NAc to specific phases of addiction, genome-wide changes in gene expression during withdrawal vs. extinction (WD/Ext) have not been examined in a context- and NAc-subregion-specific manner. Here, we used cocaine self-administration (SA) in rats combined with RNA-sequencing (RNA-seq) of NAc subregions (core and shell) to transcriptionally profile the impact of experiencing withdrawal in the home cage or in the previous drug context or experiencing extinction training. As expected, home-cage withdrawal maintained drug seeking in the previous drug context, whereas extinction training reduced it. By contrast, withdrawal involving repetitive exposure to the previous drug context increased drug-seeking behavior. Bioinformatic analyses of RNA-seq data revealed gene expression patterns, networks, motifs, and biological functions specific to these behavioral conditions and NAc subregions. Comparing transcriptomic analysis of the NAc of patients with CUD highlighted conserved gene signatures, especially with rats that were repetitively exposed to the previous drug context. Collectively, these behavioral and transcriptional correlates of several withdrawal-extinction settings reveal fundamental and translational information about potential molecular mechanisms to attenuate drug-associated memories.

neuroscience↗

bioRxiv2024

Astrocytic CREB in nucleus accumbens promotes susceptibility to chronic stress

BackgroundIncreasing evidence implicates astrocytes in stress and depression in both rodent models and human Major Depressive Disorder (MDD). Despite this, little is known about the transcriptional responses to stress of astrocytes within the nucleus accumbens (NAc), a key brain reward region, and their influence on behavioral outcomes. MethodsWe used whole cell sorting, RNA-sequencing, and bioinformatic analyses to investigate the NAc astrocyte transcriptome in male mice in response to chronic social defeat stress (CSDS). Immunohistochemistry was used to determine stress-induced changes in astrocytic CREB within the NAc. Finally, astrocytic regulation of depression-like behavior was investigated using viral-mediated manipulation of CREB in combination with CSDS. ResultsWe found a robust transcriptional response in NAc astrocytes to CSDS in stressed mice, with changes seen in both stress-susceptible and stress-resilient animals. Bioinformatic analysis revealed CREB, a transcription factor widely studied in neurons, as one of the top-predicted upstream regulators of the NAc astrocyte transcriptome, with opposite activation states seen in resilient versus susceptible mice. This bioinformatic result was confirmed at the protein level with immunohistochemistry. Viral overexpression of CREB selectively in NAc astrocytes promoted susceptibility to chronic stress. ConclusionsTogether, our data demonstrate that the astrocyte transcriptome responds robustly to CSDS and, for the first time, that transcriptional regulation in astrocytes contributes to depressive-like behaviors. A better understanding of transcriptional regulation in astrocytes may reveal unknown molecular mechanisms underlying neuropsychiatric disorders.

neuroscience↗

bioRxiv2023

Transcriptional correlates of cocaine-associated learning in striatal ARC ensembles.

Learned associations between the rewarding effects of drugs and the context in which they are experienced underlie context-induced relapse. Previous work demonstrates the importance of sparse neuronal populations - called neuronal ensembles - in associative learning and cocaine seeking, but it remains unknown whether the encoding vs. retrieval of cocaine-associated memories involves similar or distinct mechanisms of ensemble activation and reactivation in nucleus accumbens (NAc). We use ArcCreERT2 mice to establish that mostly distinct NAc ensembles are recruited by initial vs. repeated exposures to cocaine, which are then differentially reactivated and exert distinct effects during cocaine-related memory retrieval. Single-nuclei RNA-sequencing of these ensembles demonstrates predominant recruitment of D1 medium spiny neurons and identifies transcriptional properties that are selective to cocaine-recruited NAc neurons and could explain distinct excitability features. These findings fundamentally advance our understanding of how cocaine drives pathological memory formation during repeated exposures.

neuroscience↗

bioRxiv2023

Shared and divergent transcriptomic regulation in nucleus accumbens D1 and D2 medium spiny neurons by cocaine and morphine

Substance use disorders (SUDs) induce widespread molecular dysregulation in the nucleus accumbens (NAc), a brain region pivotal for coordinating motivation and reward. These molecular changes are thought to support lasting neural and behavioral disturbances that promote drug-seeking in addiction. However, different drug classes exert unique influences on neural circuits, cell types, physiology, and gene expression despite the overlapping symptomatology of SUDs. To better understand common and divergent molecular mechanisms governing SUD pathology, our goal was to survey cell-type-specific restructuring of the NAc transcriptional landscape in after psychostimulant or opioid exposure. We combined fluorescence-activated nuclei sorting and RNA sequencing to profile NAc D1 and D2 medium spiny neurons (MSNs) across cocaine and morphine exposure paradigms, including initial exposure, prolonged withdrawal after repeated exposure, and re-exposure post-withdrawal. Our analyses reveal that D1 MSNs display many convergent transcriptional responses across drug classes during exposure, whereas D2 MSNs manifest mostly divergent responses between cocaine and morphine, with morphine causing more adaptations in this cell type. Utilizing multiscale embedded gene co-expression network analysis (MEGENA), we discerned transcriptional regulatory networks subserving biological functions shared between cocaine and morphine. We observed largely integrative engagement of overlapping gene networks across drug classes in D1 MSNs, but opposite regulation of key D2 networks, highlighting potential therapeutic gene network targets within MSNs. These studies establish a landmark, cell-type-specific atlas of transcriptional regulation induced by cocaine and by morphine that can serve as a foundation for future studies towards mechanistic understanding of SUDs. Our findings, and future work leveraging this dataset, will pave the way for the development of targeted therapeutic interventions, addressing the urgent need for more effective treatments for cocaine use disorder and enhancing the existing strategies for opioid use disorder.

neuroscience↗

bioRxiv2022

Transcriptional control of nucleus accumbens neuronal excitability by Retinoid X Receptor Alpha tunes sensitivity to drug rewards

The complex nature of the transcriptional networks underlying addictive behaviors suggests intricate cooperation between diverse gene regulation mechanisms that go beyond canonical activity-dependent pathways. Here we implicate in this process a novel nuclear receptor transcription factor, Retinoid X Receptor Alpha (RXR), which we identified bioinformatically as associated with addiction-like behaviors. In the nucleus accumbens (NAc) of male and female mice, we show that, while its own expression remains unaltered after cocaine exposure, RXR controls plasticity- and addiction-relevant transcriptional programs in both dopamine receptor D1- and D2-expressing medium spiny neurons, which in turn modulate intrinsic excitability and synaptic activity of these NAc cell types. Behaviorally, bidirectional viral and pharmacological manipulation of RXR regulates drug reward sensitivity in both non-operant and operant paradigms. Together, this study demonstrates a key role for NAc RXR in promoting drug addiction, and paves the way for future studies of rexinoid signaling in psychiatric disease states.

neuroscience↗

bioRxiv2022

Region-specific CREB function regulates distinct forms of regret associated with resilience versus susceptibility to chronic stress

Regret describes recognizing that alternative actions could have led to better outcomes. This can transform into behavioral consequences, altering subsequent valuations, but remains unclear if regret derives from a generalized computation for mistake appraisal or instead is made up of dissociable action-specific processes. Using a novel neuroeconomic decision-making paradigm, we found mice were differentially sensitive to fundamentally distinct types of missed opportunities following exposure to chronic social defeat stress or manipulations of CREB, a key transcription factor implicated in chronic stress action. Bias to make compensatory decisions after rejecting high-value offers (regret type I) was unique to stress-susceptible mice. Bias following the converse operation, accepting low-value offers (regret type II), was enhanced in stress-resilient and absent in stress-susceptible mice. CREB function in either the medial prefrontal cortex or nucleus accumbens was required to suppress regret type I but differentially affected regret type II. We provide insight into how adaptive versus maladaptive stress-response traits may be related to fundamentally distinct forms of counterfactual thinking and could steer psychotherapy for mood disorders such as depression toward unveiling circuit-specific computations through a careful description of decision narrative.

neuroscience↗

bioRxiv2019

BDNF/TrkB.T1 signaling is a novel mechanism for astrocyte morphological maturation

Brain derived neurotrophic factor (BDNF) is a critical growth factor involved in the maturation of neurons, including neuronal morphology and synapse refinement. Herein, we demonstrate astrocytes express high levels of BDNFs receptor, TrkB (in the top 20 of protein-coding transcripts), with nearly exclusive expression of the truncated isoform, TrkB.T1 which peaks in expression during astrocyte morphological maturation. Using a novel culture paradigm, we show that astrocyte morphological complexity is increased in the presence of BDNF and is dependent upon BDNF/TrkB.T1 signaling. Deletion of TrkB.T1 in vivo revealed morphologically immature astrocytes with significantly reduced volume and branching, as well as dysregulated expression of perisynaptic genes associated with mature astrocyte functions, including synaptogenic genes. Indicating a role for functional astrocyte maturation via BDNF/TrkB.T1 signaling, TrkB.T1 KO astrocytes do not support normal excitatory synaptogenesis. These data suggest a significant role for BDNF/TrkB.T1 signaling in astrocyte morphological maturation, a critical process for CNS development.

neuroscience↗