Biology subjects

Maren, S.

Publications and source records attributed to Maren, S..

At least 19 recordsLinked to original sources

bioRxiv2026

Silencing basal forebrain cholinergic input to the infralimbic cortex renders fear extinction resistant to renewal

The infralimbic cortex (IL) is critical for the extinction of conditioned fear and receives dense cholinergic innervation from the basal forebrain, particularly from the horizontal limb of the diagonal band of Broca (HDB). Acetylcholine release in the IL regulates fear-related processes, but the mechanisms involved remain poorly understood. We investigated whether cholinergic projections from the HDB to the IL regulate the formation, extinction, and renewal of fear memories. Using optogenetics in male and female transgenic rats, we silenced the HDB to IL cholinergic pathway during either fear conditioning or extinction. Silencing during fear conditioning had no effect, whereas silencing during extinction enhanced extinction retrieval and prevented fear renewal. These effects were anatomically specific, as silencing the neighboring HDB to prelimbic cortex pathway had no such consequence. In ex vivo IL slices, stimulation of HDB cholinergic terminals preferentially excited interneurons over pyramidal neurons, consistent with feedforward inhibition of IL output. Finally, blockade of IL nicotinic acetylcholine receptors during extinction fully reproduced the effects of silencing the pathway, whereas muscarinic blockade attenuated renewal without affecting extinction retrieval. These findings indicate that cholinergic input from the HDB to the IL controls the acquisition and contextual specificity of extinction and identify nicotinic signaling in the IL as a potential target for improving extinction-based therapies.

neuroscience↗

bioRxiv2025

Locus Coeruleus-Amygdala Circuit Disrupts Prefrontal Control to Impair Fear Extinction

BackgroundStress undermines extinction learning and hinders exposure-based clinical therapies for a variety of neuropsychiatric disorders. In both animals and humans, dysfunction in the ventromedial prefrontal cortex (vmPFC) contributes to stress-impaired extinction, but the neural circuit by which stress modulates vmPFC function is not known. We hypothesize that the locus coeruleus (norepinephrine system (LC-NE) undermines extinction learning by recruiting projections from the basolateral amygdala (BLA) to vmPFC. MethodsWe combined chemogenetics, calcium imaging, and fiber photometry to examine how the LC-NE system influences fear extinction, with special interest to LC[->]BLA projections. We infused viral vectors into the LC, BLA, and ventromedial prefrontal cortex (vmPFC) to express designer receptors (hM3Dq) or calcium indicators (GCaMP). The LC was globally or selectively (LC[->]BLA projections) stimulated, while vmPFC and BLA activity was monitored during different stages of memory processing. Intra-BLA propranolol infusions were used to block {beta}-adrenergic receptors to test their role in LC-driven effects. ResultsWe found that chemogenetic activation of the LC increased freezing behavior, suppressed vmPFC neuronal activity, and mimicked the effects of footshock. LC stimulation impaired both delayed and immediate extinction learning, while activation of the LC[->]BLA pathway alone was sufficient to drive the immediate extinction deficit. LC activation increased activity in BLA neurons projecting to vmPFC, and this effect, as well as vmPFC suppression, was prevented by {beta}-adrenergic blockade with propranolol in the BLA. Overall, LC-driven NE release in the BLA disrupted vmPFC activity and dynamics, promoted a high-stress stated and impaired fear extinction. ConclusionThis study demonstrates that stress and LC activation promote NE release in the BLA, which disrupts vmPFC activity and impairs fear extinction. These findings identify the LC-BLA-vmPFC circuit as a key pathway through which stress undermines extinction learning, highlighting BLA {beta}-adrenergic receptors as potential therapeutic targets for stress-related disorders like PTSD.

neuroscience↗

bioRxiv2025

Theta-paced stimulation of the thalamic nucleus reuniens en-trains mPFC-HPC oscillations and facilitates the acquisition of extinction memories

BackgroundThe nucleus reuniens (RE) is a midline thalamic nucleus interconnecting the medial prefrontal cortex (mPFC) and the hippocampus (HPC), structures known to be involved in aversive memory processes. Recent work indicates that the RE plays a critical role in the acquisition and retrieval of fear extinction memories. Functional inactivation of the RE impairs both mPFC-HPC coherence and extinction memory. Here we examine whether imposing theta activity on the RE entrains oscillations in the mPFC and HPC and facilitates extinction learning. MethodsTo deliver theta-paced (8 Hz) optogenetic stimulation, we expressed an excitatory opsin, (channelrhodopsin; AAV9-CaMKIIa-hChR2(H134R)-mCherry) or control virus (AAV9-CaMKIIa-mCherry) in the RE in male and female rats. A single optic fiber targeting the RE was implanted during the same surgery. After recovery, animals underwent auditory fear conditioning, extinction training, and an extinction retrieval test, each separated by 24-h. During extinction training, conditioned stimuli (CS) presentations were paired with 8-Hz sinusoidal optostimulation (473 nM, 10 mW) of the RE. In another experiment, we recorded local field potentials (LFPs) from the mPFC and dorsal HPC during using these behavioral procedures. ResultsTheta-paced stimulation of the RE during extinction training significantly decreased freezing behavior compared to the control group. Notably, the reduction in conditioned behavior was evident during the subsequent stimulation-free retrieval test. This reveals that RE stimulation during extinction not only suppresses conditioned fear responses acutely, but also facilitates the acquisition of long-term extinction memories. Theta-paced RE stimulation markedly enhanced both neural activity and entrained theta oscillations in the mPFC and dHPC. ConclusionThis work suggests that the RE oscillatory activity is critical for the acquisition of extinction memories through the modulation of hippocampal-prefrontal network dynamics. In the future, RE theta-paced stimulation can be an important therapeutic tool by strengthening extinction memories.

neuroscience↗

bioRxiv2025

Neural Representation of Associative Threat Learning in Pulvinar Divisions, Lateral Geniculate Nucleus, and Mediodorsal Thalamus in Humans

Understanding the neural mechanisms underlying associative threat learning is essential for advancing behavioral models of threat and adaptation. We investigated distinct activation patterns across thalamic pulvinar divisions, the lateral geniculate nucleus (LGN), and the mediodorsal thalamus (MD) during associative threat learning using fMRI. The anterior pulvinar and MD exhibited parallel activation patterns, that may reflect distinct contributions to automatic and more deliberative learning processes. Additionally, our findings suggest a hierarchical functional organization of pulvinar activation during fear conditioning, in which coordinated activation among inferior, lateral, medial, and anterior divisions may support the integration of threat-related information. Pulvinar divisions and the MD showed activation during extinction learning and exhibited activation patterns consistent with salience processing during extinction recall and threat renewal. LGN activation patterns were consistent with feedforward visual processing. These findings extend current models of threat learning and memory by suggesting distinct patterns of thalamic involvement across associative threat learning and memory and providing a functional framework for investigating thalamic contributions to these processes.

neuroscience↗

bioRxiv2025

Hippocampal-prelimbic coupling during context-dependent extinction retrieval in rats

After fear conditioning, repeated presentation of the conditioned stimulus (CS) alone produces a context-dependent extinction of learned fear. The hippocampus has a critical role in this process, but the mechanism by which contextual information encoded by the hippocampus leads to fear suppression is unknown. We hypothesize that contextual information encoded by the dorsal hippocampus supports the recall of extinction memory by the medial prefrontal cortex (mPFC). To test this hypothesis, we evaluated the oscillatory coherence and directional coupling of the hippocampus and mPFC during context-dependent extinction retrieval in a previously published experiment. In this experiment, male and female rats were subjected to auditory fear conditioning followed by fear extinction and extinction retrieval procedures. Previous analyses focused on oscillatory coupling during the CS; here, we performed new analyses to assess hippocampal-prefrontal coupling in the context in which extinction occurred. We found that, after extinction, re-exposing the animals to the extinction context produces a marked increase in dorsal hippocampal theta (6-8 Hz) oscillations. This increase was associated with enhanced coherence with the prelimbic (PL), but not the infralimbic (IL), division of the mPFC. Moreover, Granger causality analyses revealed that hippocampal theta oscillations preceded theta in the PL throughout the extinction retrieval session. This effect emerged during exposure to the extinction context and persisted during the presentation of the CSs and the expression of freezing behavior. Interestingly, this pattern of coherence was not observed in the IL. These results reveal that oscillatory coupling between the dorsal hippocampus and PL facilitates the context-dependent retrieval of the extinguished fear memory.

neuroscience↗

bioRxiv2025

Functional synaptic connectivity of engrafted spinal cord neurons with locomotor circuitry in the injured spinal cord

Spinal cord injury (SCI) results in significant neurological deficits, with no currently available curative therapies. Neural progenitor cell (NPC) transplantation has emerged as a promising approach for neural repair, as graft-derived neurons (GDNs) can integrate into the host spinal cord and support axon regeneration. However, the mechanisms underlying functional recovery remain poorly understood. In this study, we investigate the synaptic integration of NPC-derived neurons into locomotor circuits, the projection patterns of distinct neuronal subtypes, and their potential to modulate motor circuit activity. Using transsynaptic tracing in a mouse thoracic contusion SCI model, we found that NPC-derived neurons form synaptic connections with host locomotor circuits, albeit at low frequencies. Furthermore, we mapped the axon projections of V0C and V2a interneurons, revealing distinct termination patterns within host spinal cord laminae. To assess functional integration, we employed chemogenetic activation of GDNs, which induced muscle activity in a subset of transplanted animals. However, NPC transplantation alone did not significantly improve locomotor recovery, highlighting a key challenge in the field. Our findings suggest that while GDNs can integrate into host circuits and modulate motor activity, synaptic connectivity remains a limiting factor in functional recovery. Future studies should focus on enhancing graft-host connectivity and optimizing transplantation strategies to maximize therapeutic benefits for SCI.

neuroscience↗

bioRxiv2025

Associative coding of conditioned fear in the thalamic nucleus reuniens in rodents and humans

The nucleus reuniens (RE) is a midline thalamic structure interconnecting the medial prefrontal cortex (mPFC) and the hippocampus (HPC). Recent work in both rodents and humans implicates the RE in the adaptive regulation of emotional memories, including the suppression of learned fear. However, the neural correlates of aversive learning in the RE of rodents and humans remains unclear. To address this, we recorded RE activity in humans (BOLD fMRI) and rats (fiber photometry) during Pavlovian fear conditioning and extinction. In both rats and humans, we found that conditioned stimulus (CS)-evoked activity in RE reflects the associative value of the CS. In rats, we additionally found that spontaneous neural activity in RE tracks defensive freezing and shows anticipatory increases in calcium activity that precede the termination of freezing behavior. Single-unit recordings in rats confirmed that individual RE neurons index both the associative value of the CS and defensive behavior transitions. Moreover, distinct neuronal ensembles in the RE encode fear versus extinction memories. These findings suggest a conserved role of the RE across species in modulating defensive states and emotional memory processes, providing a foundation for future translational research on fear-related disorders.

neuroscience↗

bioRxiv2024

Acute stress yields a sex-dependent facilitation of signaled active avoidance in rats

Post-traumatic stress disorder (PTSD) is a debilitating disorder characterized by excessive fear, hypervigilance, and avoidance of thoughts, situations or reminders of the trauma. Among these symptoms, relatively little is known about the etiology of pathological avoidance. Here we sought to determine whether acute stress influences avoidant behavior in adult male and female rats. We used a stress procedure (unsignaled footshock) that is known to induce long-term sensitization of fear and potentiate aversive learning. Rats were submitted to the stress procedure and, one week later, underwent two-way signaled active avoidance conditioning (SAA). In this task, rats learn to prevent an aversive outcome (shock) by performing a shuttling response when exposed to a warning signal (tone). We found that acute stress significantly enhanced SAA acquisition rate in females, but not males. Female rats exhibited significantly greater avoidance responding on the first day of training relative to controls, reaching similar levels of performance by the second day. Males that underwent the stress procedure showed similar rates of acquisition to controls but exhibited resistance to extinction. This was manifest as both elevated avoidance and intertrial responding across extinction days relative to non-stressed controls, an effect that was not observed in females. In a second experiment, acute stress sensitized footshock unconditioned responses in males, not females. However, males and females exhibited similar levels of stress-enhanced fear learning (SEFL), which was expressed as sensitized freezing to a shock-paired context. Together, these results reveal that acute stress facilitates SAA performance in both male and female rats, though the nature of this effect is different in the two sexes. We did not observe sex differences in SEFL, suggesting that the stress-induced sex difference in performance was selective for instrumental avoidance. Future work will elucidate the neurobiological mechanisms underlying the differential effect of stress on instrumental avoidance in male and female rats.

neuroscience↗

bioRxiv2024

Pharmacological stimulation of infralimbic cortex after fear conditioning facilitates subsequent fear extinction

The infralimbic (IL) division of the medial prefrontal cortex (mPFC) is a crucial site for extinction of conditioned fear memories in rodents. Recent work suggests that neuronal plasticity in the IL that occurs during (or soon after) fear conditioning enables subsequent IL-dependent extinction learning. We therefore hypothesized that pharmacological activation of the IL after fear conditioning would promote the extinction of conditioned fear. To test this hypothesis, we characterized the effects of post-conditioning infusions of the GABAA receptor antagonist, picrotoxin, into the IL on extinction of auditory conditioned freezing in male and female rats. In four experiments, we found that picrotoxin injections performed immediately, 24 hours, or 13 days after fear conditioning reduced conditioned freezing to the auditory conditioned stimulus (CS) during both extinction training and extinction retrieval; this effect was observed up to two weeks after picrotoxin infusions. Interestingly, inhibiting protein synthesis inhibition in the IL immediately after fear conditioning prevented the inhibition of freezing by picrotoxin injected 24 hours later. Our data suggest that the IL encodes an inhibitory memory during the consolidation of fear conditioning that is necessary for future fear suppression.

neuroscience↗

bioRxiv2024

Ventral hippocampus mediates inter-trial responding in signaled active avoidance

The hippocampus has a central role in regulating contextual processes in memory. We have shown that pharmacological inactivation of ventral hippocampus (VH) attenuates the context-dependence of signaled active avoidance (SAA) in rats. Here, we explore whether the VH mediates intertrial responses (ITRs), which are putative unreinforced avoidance responses that occur between trials. First, we examined whether VH inactivation would affect ITRs. Male rats underwent SAA training and subsequently received intra-VH infusions of saline or muscimol before retrieval tests in the training context. Rats that received muscimol performed significantly fewer ITRs, but equivalent avoidance responses, compared to controls. Next, we asked whether chemogenetic VH activation would increase ITR vigor. In male and female rats expressing excitatory (hM3Dq) DREADDs, systemic CNO administration produced a robust ITR increase that was not due to nonspecific locomotor effects. Then, we examined whether chemogenetic VH activation potentiated ITRs in an alternate (non-training) test context and found it did. Finally, to determine if context-US associations mediate ITRs, we exposed rats to the training context for three days after SAA training to extinguish the context. Rats submitted to context extinction did not show a reliable decrease in ITRs during a retrieval test, suggesting that context-US associations are not responsible for ITRs. Collectively, these results reveal an important role for the VH in context-dependent ITRs during SAA. Further work is required to explore the neural circuits and associative basis for these responses, which may be underlie pathological avoidance that occurs in humans after threat has passed.

neuroscience↗

bioRxiv2022

Thalamic nucleus reuniens coordinates prefrontal-hippocampal synchrony to suppress extinguished fear

Traumatic events result in vivid and enduring fear memories. Suppressing the retrieval of these memories is central to behavioral therapies for pathological fear. The medial prefrontal cortex (mPFC) and hippocampus (HPC) have been implicated in retrieval suppression, but how mPFC-HPC activity is coordinated during extinction retrieval is unclear. Here we show that after extinction training, coherent theta oscillations (6-9 Hz) in the HPC and mPFC are correlated with the suppression of conditioned freezing in male and female rats. Inactivation of the nucleus reuniens (RE), a thalamic hub interconnecting the mPFC and HPC, reduces extinction-related Fos expression in both the mPFC and HPC, dampens mPFC-HPC theta coherence, and impairs extinction retrieval. Conversely, theta-paced optogenetic stimulation of RE augments fear suppression and reduces relapse of extinguished fear. Collectively, these results demonstrate a novel role for RE in coordinating mPFC-HPC interactions to suppress fear memories after extinction.

neuroscience↗

bioRxiv2022

Sex differences in the immediate extinction deficit and renewal of extinguished fear in rats

Extinction learning is central to exposure-based behavioral therapies for reducing fear and anxiety in humans. However, patients with fear and anxiety disorders are often resistant to extinction. Moreover, trauma and stress-related disorders are highly prone to relapse and are twice as likely to occur in females compared to males, suggesting that females may be more susceptible to extinction deficits and fear relapse phenomena. In this report, we tested this hypothesis by examining sex differences in a stress-induced extinction learning impairment, the immediate extinction deficit (IED), and renewal, a common form of fear relapse. In contrast to our hypothesis, there were no sex differences in the magnitude of the immediate extinction deficit in two different rat strains (Long-Evans and Wistar). However, we did observe a sex difference in the renewal of fear when the extinguished conditioned stimulus was presented outside the extinction context. Male Wistar rats exhibited significantly greater renewal than female rats, a sex difference that has previously been reported after appetitive extinction. Collectively, these data reveal that stress-induced extinction impairments are similar in male and female rats, though the context-dependence of extinction is more pronounced in males.

animal behavior and cognition↗

bioRxiv2021

Convergent coding of recent and remote fear memory in the basolateral amygdala

BackgroundIn both rodents and humans, the basolateral amygdala (BLA) is essential for encoding and retrieving conditioned fear memories. Although the BLA is a putative storage site for these memories, recent evidence suggests that they become independent of the BLA with the passage of time. MethodsWe systematically examined the role for the BLA in the retrieval of recent (1 day) and remote (2 weeks) fear memory using optogenetic, electrophysiological, and calcium imaging methods in male and female Long-Evans rats. Critically, we used a behavioral design that permits within-subjects comparison of recent and remote memory at the same time point; freezing behavior served as the index of learned fear. ResultsWe found that BLA c-Fos expression was similar after the retrieval of recent or remote fear memories. Extracellular single-unit recordings in awake, behaving animals revealed that single BLA neurons exhibit robust increases in spike firing to both recent and remote conditional stimuli (CSs). Fiber photometry recordings revealed that these patterns of activity emerge from principal neurons. Consistent with these results, optogenetic inhibition of BLA principal neurons impaired conditioned freezing to both recent and remote CSs. There were no sex differences in any of the measures or manipulations. ConclusionsThese data reveal that BLA neurons encode both recent and remote fear memories, suggesting substantial overlap in the allocation of temporally distinct events. This may underlie the broad generalization of fear memories across both space and time. Ultimately, these results provide evidence that the BLA is a long-term storage site for emotional memories.

neuroscience↗

bioRxiv2021

AI-driven high-throughput automation of behavioral analysis and dual-channel wireless optogenetics for multiplexing brain dynamics

Advances in behavioral optogenetics are limited by the absence of high-throughput pipelines for the automated analysis of behavior in freely behaving animals. Although a variety of AI algorithms has been proposed that enable automation of behavioral analysis, existing methods are generally low-throughput. In addition, optogenetic manipulation of neural circuits typically requires physical tethers to light sources, which limits the number of brain areas that can be targeted and thus constrains behavioral testing. Here, we develop a new wireless platform that combines a battery-free dual-channel optogenetic implant with an AI algorithm for high-throughput behavioral analysis. In our platform, a customized AI algorithm detected and quantified freezing behavior of rats that had undergone fear conditioning. Notably, our platform allows up to four enclosures to be monitored simultaneously. Wireless dual-channel optogenetic devices were implanted in the basolateral amygdala (BLA) to permit independent modulation of BLA principal neurons (red light, AAV-CaMKII-JAWS) or BLA interneurons (blue light, AAV-mDlx-ChR2) in freely behaving animals. In vivo validation with behaving rats demonstrates the utility of the telemetry system for large-scale optogenetic studies. SignificanceAI algorithms can enable automation of behavioral analysis and thereby facilitate the progress on behavioral optogenetics. Successful integration of advanced wireless dual-channel optoelectronic devices with biological systems can also yield new tools and techniques for neuroscience research, particularly in the context of techniques for optogenetics. Here, we propose a new approach that combines an advanced AI algorithm with a low power wireless telemetry system, yielding powerful capabilities in the understanding of brain functions and the evaluation of the behavioral consequences of neural circuit manipulations. In vivo studies using optimized systems demonstrate high-throughput automation of behavioral manipulation and analysis via AI-powered wireless telemetry.

neuroscience↗

bioRxiv2021

Ventral hippocampus mediates the context-dependence of two-way signaled avoidance in male rats

Considerable work indicates that instrumental responding is context-dependent, but the neural mechanisms underlying this phenomenon are poorly understood. Given the important role for the hippocampal formation in contextual processing, we hypothesized that reversible inactivation of the hippocampus would impair the context-dependence of active avoidance. To test this hypothesis, we used a two-way signaled active avoidance (SAA) task that requires rats to shuttle across a divided chamber during a tone CS in order to avoid a footshock US. After training, avoidance responding was assessed in an extinction test in both the training context and a novel context in a counterbalanced order. Rats performed significantly more avoidance responses in the training context than in the novel context, demonstrating the context-dependence of shuttle avoidance behavior. To examine the role of the hippocampus in the context-dependence of SAA, we reversibly inactivated either the dorsal (DH) or ventral hippocampus (VH) prior to testing. Inactivation of the VH eliminated the context-dependence of SAA and elevated avoidance responding in the novel context to levels similar to that expressed in the training context. In contrast, DH inactivation had no effect on avoidance in either context, and neither manipulation affected freezing behavior. Therefore, the integrity of the VH, but not DH, is required for the expression context-dependence of avoidance behavior.

neuroscience↗

bioRxiv2021

Behavioral and brain mechanisms mediating conditioned flight behavior in rats

Environmental contexts and associative learning can inform animals of potential threats, though it is currently unknown how contexts bias defensive transitions. Here we investigated context-dependent flight responses in the Pavlovian serial-compound stimulus (SCS) paradigm. We show here that SCS-evoked flight behavior in male and female rats is dependent on contextual fear. Flight was reduced in the conditioning context after context extinction and could be evoked in a different shock-associated context. Although flight was exclusive to white noise stimuli, it was nonetheless associative insofar as rats that received an equal number of unpaired USs did not show flight-like behavior. Finally, we found that inactivation of either the central nucleus of the amygdala (CeA) or bed nucleus of the stria terminalis (BNST) attenuated both contextual fear and flight responses. This work demonstrates that contextual fear summates with cued and innate fear to drive a high fear state and freeze-to-flight transitions.

neuroscience↗

bioRxiv2019

Threat imminence dictates the role of the bed nucleus of the stria terminalis in contextual fear

Previous work indicates that the bed nucleus of the stria terminalis (BNST) is involved in defensive freezing to unpredictable Pavlovian conditioned stimuli (Goode et al., 2019). Here we show that the BNST mediates freezing to contexts paired with remote (unpredictable), but not imminent (predictable), footshock. Rats underwent a fear conditioning procedure in which a single footshock unconditioned stimulus (US) was delivered either 1 (imminent) or 9 minutes (remote) after placement in the context; each rat received a total of four conditioning trials over two days. Contexts associated with either imminent or remote USs produced distinct patterns of freezing and shock-induced activity but freezing in each case was context-dependent. Reversible inactivation of the BNST reduced the expression of contextual freezing in the context paired with remote, but not imminent, footshock. Implications of these data are discussed in light of recent conceptualizations of BNST function, as well as for anxiety behaviors.

neuroscience↗

bioRxiv2018

Bed nucleus of the stria terminalis mediates fear to ambiguous threat signals

The bed nucleus of the stria terminalis (BNST) has been implicated in fear and anxiety, but the specific factors that engage the BNST in defensive behavior are unclear. Here we explore the possibility that ambiguous threats recruit the BNST during Pavlovian fear conditioning in rats. We arranged a conditioned stimulus (CS) to either precede or follow an aversive unconditioned stimulus (US), a procedure that established reliable (forward) or ambiguous (backward) signals for US onset. After conditioning, reversible inactivation of the BNST selectively reduced freezing to the backward CS; BNST inactivation did not affect freezing to the forward CS even when that CS predicted a variable magnitude US. Backward CSs increased Fos in the ventral BNST and in BNST-projecting neurons in the infralimbic cortex, but not the hippocampus or amygdala. These data reveal that BNST circuits process ambiguous threat signals central to the etiology and expression of anxiety.

neuroscience↗