Biology subjects

Denny, C. A.

Publications and source records attributed to Denny, C. A..

14 recordsLinked to original sources

bioRxiv2025

Novel, small molecules targeting the 5-HT4R receptor protect against stress-induced maladapative behavior with efficacy across age

BACKGROUNDStress is a risk factor for developing psychiatric disorders, including major depressive disorder (MDD). Compounds targeting the serotonin type 4 receptor (5-HT4R) hold promise as novel rapid-acting treatments of mood disorders. However, a lack of selectivity and numerous side effects have been limiting factors for their clinical use. Here, we developed and characterized novel-composition 5-HT4R compounds in mouse models of stress. METHODSThree 5-HT4R-targeting compounds were designed and synthesized based on PF-04995274, a high-affinity 5-HT4R ligand reported to be a partial agonist. G-protein assays were utilized to characterize molecular activity. Saline, PF-04995274, or a novel compound were administered before or after stress in male and female mice. Drug effects were assayed using behavioral paradigms. Patch clamp electrophysiology was used to determine the effect of drug on glutamatergic activity in hippocampal Cornu Ammonis 3 (CA3). RESULTSProphylactic administration of DL5, DL7, or DL8 was effective at reducing stress-induced maladaptive behaviors in male and female mice; DL7 and DL8 were effective when administered after stress. When administered following learned helplessness (LH), DL7 reduced behavioral despair and increased c-Fos in the dentate gyrus (DG) and CA3. All novel compounds attenuated large-amplitude AMPA receptor-mediated bursts in ventral CA3 (vCA3). In aged male mice, prophylactic DL7 reduced behavioral despair. CONCLUSIONSThese results characterize novel 5-HT4R-targeting compounds for stress-induced psychiatric disease with the potential to address unmet needs in adult and aged patients with stress-induced psychiatric illness. Future work will characterize their mechanism of action with the goal of clinical development.

neuroscience↗

bioRxiv2025

Altered striatal dopamine regulation in ADGRL3 knockout mice

Dopaminergic signaling is essential for regulating movement, learning, and reward. Disruptions in this system are linked to neuropsychiatric disorders such as ADHD. ADGRL3, an adhesion G protein-coupled receptor highly expressed in the brain, is genetically associated with increased ADHD risk. ADGRL3 knockout in animals alters expression of dopaminergic markers and induces dopamine-related behavioral changes. However, its precise role in modulating dopamine signaling remains unclear. We investigated how ADGRL3 knockout affects striatal dopamine release in mice using ex vivo fast-scan cyclic voltammetry and in vivo fiber photometry with a dopamine sensor. Ex vivo measurements showed increased electrically-evoked dopamine release across the striatum. Conversely, in vivo recordings revealed reduced task-induced dopamine signals in the nucleus accumbens during an operant fixed interval task. This reduction was not due to impaired dopamine availability, as amphetamine-evoked release was unchanged. These findings suggest ADGRL3 modulates dopamine release in complex ways via different pre- and postsynaptic mechanisms.

neuroscience↗

bioRxiv2025

Brainwide genetic capture for conscious state transitions

Neural circuits underlying unconsciousness remain poorly defined. We test the hypothesis that unconsciousness arises from specific, distributed circuits using general anesthesia in mice as a reproducible model. We identify a cortical-to-subcortical shift in neural activity during isoflurane anesthesia that is organized into nine discrete functional communities mapped at single-cell resolution. The lateral parabrachial nucleus (LPB) emerges as a central hub, exhibiting high interconnectivity, spontaneous firing under anesthesia, and preferential recruitment during reactivation of the brain-wide ensemble confirmed by single unit recordings. Chemogenetic reactivation of the captured brain-wide ensemble induces sedation, slow wave oscillations, hypothermia, and analgesia, which are components of anesthesia-induced unconsciousness. Reactivation of the LPB ensemble alone recapitulates a subset of these effects. Together, we define a global neural substrate for unconsciousness and recapitulate its dissociable autonomic, neurophysiologic, and behavioral effects using brain-wide ensemble manipulations. These results establish a neural circuit framework for anesthesia-induced unconsciousness in the mammalian brain.

neuroscience↗

bioRxiv2024

A SMARTR workflow for multi-ensemble atlas mapping and brain-wide network analysis

In the last decade, activity-dependent strategies for labelling multiple immediate early gene (IEG) ensembles in mice have generated unprecedented insight into the mechanisms of memory encoding, storage, and retrieval. However, few strategies exist for brain-wide mapping of multiple ensembles, including their overlapping population, and none incorporate capabilities for downstream network analysis. Here, we introduce a scalable workflow to analyze traditionally coronally-sectioned datasets produced by activity-dependent tagging systems. Intrinsic to this pipeline is simple multi-ensemble atlas registration and statistical testing in R (SMARTTR), an R package which wraps mapping capabilities with functions for statistical analysis and network visualization, and support for import of external datasets. We demonstrate the versatility of SMARTTR by mapping the ensembles underlying the acquisition and expression of learned helplessness (LH), a robust stress model. Applying network analysis, we find that exposure to inescapable shock (IS), compared to context training (CT), results in decreased centrality of regions engaged in spatial and contextual processing and higher influence of regions involved in somatosensory and affective processing. During LH expression, the substantia nigra emerges as a highly influential region which shows a functional reversal following IS, indicating a possible regulatory function of motor activity during helplessness. We also report that IS results in a robust decrease in reactivation activity across a number of cortical, hippocampal, and amygdalar regions, indicating suppression of ensemble reactivation may be a neurobiological signature of LH. These results highlight the emergent insights uniquely garnered by applying our analysis approach to multiple ensemble datasets and demonstrate the strength of our workflow as a hypothesis-generating toolkit.

neuroscience↗

bioRxiv2024

Ketamine metabolism via hepatic CYP450 isoforms contributes to its sustained antidepressant actions.

(R,S)-ketamine (ketamine) has rapid and sustained antidepressant (AD) efficacy at sub-anesthetic doses in depressed patients. A metabolite of ketamine, including (2R,6R)-hydroxynorketamine ((6)-HNKs) has been reported to exert antidepressant actions in rodent model of anxiety/depression. To further understand the specific role of ketamines metabolism in the AD actions of the drug, we evaluated the effects of inhibiting hepatic cytochrome P450 enzymes on AD responses. We assessed whether pre-treatment with fluconazole (10 and 20 mg/kg, i.p.) 1 hour prior to ketamine or HNKs (10 mg/kg, i.p.) administration would alter behavioral and neurochemical actions of the drugs in male BALB/cJ mice with a highly anxious phenotype. Extracellular microdialysate levels of glutamate and GABA (Gluext, GABAext) were also measured in the medial prefrontal cortex (mPFC). Pre-treatment with fluconazole altered the pharmacokinetic profile of ketamine, by increasing both plasma and brain levels of ketamine and (R,S)-norketamine, while robustly reducing those of (6)-HNKs. At 24 hours post-injection (t24h), fluconazole prevented the sustained AD-like response of ketamine responses in the forced swim test and splash test, as well as the enhanced cortical GABA levels produced by ketamine. A single (2R,6R)-HNK administration selectively rescued the antidepressant-like activity of ketamine in mice pretreated with fluconazole within 24 hours of treatment. Overall, these findings are consistent with an essential role of (6)-HNK in mediating the sustained antidepressant-like effects of ketamine and suggest potential interactions between pharmacological CYPIs and ketamine during antidepressant treatment in patients.

neuroscience↗

bioRxiv2024

A multiple Arc (mArc) tagging system to uncover the organizational principles of multiple memories

Engrams or memory traces are the neuronal ensembles that collectively store individual experiences. Genetic strategies based on immediate early genes (IEGs), such as Arc/Arg3.1, allow us to tag the ensembles active during memory encoding and compare them to those active during retrieval. However, these strategies only allow for the tagging of one neural ensemble. Here, we developed a multiple Arc (mArc) system that allows for the tagging of two Arc+ ensembles. We validated this system by investigating how context, time, and valence influence neuronal ensemble reactivation in the dentate gyrus (DG). We show that similar contextual and valenced experiences are encoded in overlapping DG ensembles. We also find that ensembles are modulated by time, where experiences closer in time are encoded in more similar ensembles. These results highlight the dynamic nature of DG ensembles and show that the mArc system provides a powerful approach for investigating multiple memories in the brain. HIGHLIGHTSO_LIThe mArc system allows for the tagging of two Arc+ ensembles in the same mouse C_LIO_LIDG ensembles labeled by the mArc system receive increased excitatory input C_LIO_LIContext, valence, and time influence DG ensemble reactivation C_LIO_LIDG neural ensembles are reactivated less with increasing time C_LI

neuroscience↗

bioRxiv2023

(R,S)-ketamine's rapid-acting antidepressant effects are modulated by NR2B- containing NMDA receptors on adult-born hippocampal neurons

Standard antidepressant treatments often take weeks to reach efficacy and are ineffective for many patients. (R,S)-ketamine, an N-methyl-D-aspartate (NMDA) antagonist, has been shown to be a rapid-acting antidepressant and to decrease depressive symptoms within hours of administration. While previous studies have shown the importance of the NR2B subunit of the NMDA receptor (NMDAR) on interneurons in the medial prefrontal cortex (mPFC), no study has investigated the influence of NR2B-expressing adult-born granule cells (abGCs). In this study, we examined whether (R,S)-ketamines efficacy depends upon these adult-born hippocampal neurons using a genetic strategy to selectively ablate the NR2B subunit of the NMDAR from Nestin+ cells. To validate our findings, we also used several other transgenic lines including one in which NR2B was deleted from an interneuron (Parvalbumin (PV)+) population. We report that in male mice, NR2B expression on 6-week-old adult-born neurons is necessary for (R,S)-ketamines effects on behavioral despair in the forced swim test (FST) and on hyponeophagia in the novelty suppressed feeding (NSF) paradigm, as well on fear behavior following contextual fear conditioning (CFC). In female mice, NR2B expression is necessary for effects on hyponeophagia in the NSF. We also find that ablating neurogenesis increases fear expression in CFC, which is buffered by (R,S)-ketamine administration. In line with previous studies, these results suggest that 6-week-old adult-born hippocampal neurons expressing NR2B partially modulate (R,S)-ketamines rapid-acting effects. Future work targeting these 6-week-old adult-born neurons may prove beneficial for increasing the efficacy of (R,S)-ketamines antidepressant actions.

neuroscience↗

bioRxiv2023

A tale of two receptors: simultaneous targeting of NMDARs and 5-HT4Rs exerts additive effects against stress

BACKGROUNDSerotonin (5-HT) receptors and N-methyl-D-aspartate receptors (NMDARs) have both been implicated in the pathophysiology of depression and anxiety disorders. Here, we evaluated whether targeting both receptors through combined dosing of (R,S)-ketamine, an NMDAR antagonist, and prucalopride, a serotonin type IV receptor (5-HT4R) agonist, would have additive effects, resulting in reductions in stress-induced fear, behavioral despair, and hyponeophagia. METHODSA single injection of saline (Sal), (R,S)-ketamine (K), prucalopride (P), or a combined dose of (R,S)-ketamine and prucalopride (K+P) was administered before or after contextual fear conditioning (CFC) stress in both sexes. Drug efficacy was assayed using the forced swim test (FST), elevated plus maze (EPM), open field (OF), marble burying (MB), and novelty-suppressed feeding (NSF). Patch clamp electrophysiology was used to measure the effects of combined drug on neural activity in hippocampal CA3. c-fos and parvalbumin (PV) expression in the hippocampus (HPC) and medial prefrontal cortex (mPFC) was examined using immunohistochemistry and network analysis. RESULTSWe found that a combination of K+P, given before or after stress, exerted additive effects, compared to either drug alone, in reducing a variety of stress-induced behaviors in both sexes. Combined K+P administration significantly altered c-fos and PV expression and network activity in the HPC and mPFC. CONCLUSIONSOur results indicate that combined K+P has additive benefits for combating stress-induced pathophysiology, both at the behavioral and neural level. Our findings provide preliminary evidence that future clinical studies using this combined treatment strategy may prove advantageous in protecting against a broader range of stress-induced psychiatric disorders.

neuroscience↗

bioRxiv2023

Sex-Specific Effects of Anxiety on Cognition and Activity-Dependent Neural Networks: Insights from (Female) Mice and (Wo)Men

INTRODUCTIONNeuropsychiatric symptoms (NPS), such as depression and anxiety, are observed in 90% of Alzheimers disease (AD) patients, two-thirds of whom are women. NPS usually manifest long before AD onset creating a therapeutic opportunity. Here, we examined the impact of anxiety on AD progression and the underlying brain-wide neuronal mechanisms. METHODSTo gain mechanistic insight into how anxiety impacts AD progression, we performed a cross-sectional analysis on mood, cognition, and neural activity utilizing the ArcCreERT2 x enhanced yellow fluorescent protein (eYFP) x APP/PS1 (AD) mice. The ADNI dataset was used to determine the impact of anxiety on AD progression in human subjects. RESULTSFemale AD mice exhibited anxiety-like behavior and cognitive decline at an earlier age than control (Ctrl) mice and male mice. Brain-wide analysis of c-Fos+ revealed changes in regional correlations and overall network connectivity in AD mice. Sex-specific memory trace changes were observed; female AD mice exhibited impaired memory traces in dorsal CA3 (dCA3), while male AD mice exhibited impaired memory traces in the dorsal dentate gyrus (dDG). In the ADNI dataset, anxiety predicted transition to dementia. Female subjects positive for anxiety and amyloid transitioned more quickly to dementia than male subjects. CONCLUSIONSWhile future studies are needed to understand whether anxiety is a predictor, a neuropsychiatric biomarker, or a comorbid symptom that occurs during disease onset, these results suggest that AD network dysfunction is sexually dimorphic, and that personalized medicine may benefit male and female AD patients rather than a one size fits all approach.

neuroscience↗

bioRxiv2023

Traumatic brain injury-induced fear generalization in mice involves hippocampal memory trace dysfunction and is alleviated by (R,S)-ketamine

INTRODUCTIONTraumatic brain injury (TBI) is a debilitating neurological disorder caused by an impact to the head by an outside force. TBI results in persistent cognitive impairments, including fear generalization, the inability to distinguish between aversive and neutral stimuli. The mechanisms underlying fear generalization have not been fully elucidated, and there are no targeted therapeutics to alleviate this symptom of TBI. METHODSTo identify the neural ensembles mediating fear generalization, we utilized the ArcCreERT2 x enhanced yellow fluorescent protein (EYFP) mice, which allow for activity-dependent labeling and quantification of memory traces. Mice were administered a sham surgery or the controlled cortical impact (CCI) model of TBI. Mice were then administered a contextual fear discrimination (CFD) paradigm and memory traces were quantified in numerous brain regions. In a separate group of mice, we tested if (R,S)-ketamine could decrease fear generalization and alter the corresponding memory traces in TBI mice. RESULTSTBI mice exhibited increased fear generalization when compared with sham mice. This behavioral phenotype was paralleled by altered memory traces in the DG, CA3, and amygdala, but not by alterations in inflammation or sleep. In TBI mice, (R,S)-ketamine facilitated fear discrimination and this behavioral improvement was reflected in DG memory trace activity. CONCLUSIONSThese data show that TBI induces fear generalization by altering fear memory traces, and that this deficit can be improved with a single injection of (R,S)-ketamine. This work enhances our understanding of the neural basis of TBI-induced fear generalization and reveals potential therapeutic avenues for alleviating this symptom.

animal behavior and cognition↗

bioRxiv2020

PKMζ traces hippocampal LTP maintenance and spatial long-term memory

PKM{zeta} is an autonomously active PKC isoform crucial for the maintenance of synaptic long-term potentiation (LTP) and long-term memory. Unlike other protein kinases that are transiently stimulated by second messengers, PKM{zeta} is persistently activated through sustained increases in kinase protein expression. Therefore, visualizing increases in PKM{zeta} expression during long-term memory storage might reveal the sites of its persistent action and thus the location of memory-associated LTP maintenance in the brain. Using quantitative immunohistochemistry validated by the lack of staining in PKM{zeta}-null mice, we examined the amount and distribution of PKM{zeta} in subregions of the hippocampal formation of wild-type mice during LTP maintenance and spatial long-term memory storage. During LTP maintenance in hippocampal slices, PKM{zeta} increases in the pyramidal cell body and stimulated dendritic layers of CA1 for at least 2 h. During spatial memory storage, PKM{zeta} increases in CA1 pyramidal cells for at least 1 month, paralleling the persistence of the memory. The subset of CA1 pyramidal cells that are tagged by immediate early gene Arc-driven transcription of fluorescent proteins, whose expression increases during initial memory formation, also expresses the persistent increase of PKM{zeta} during memory storage. In the memory-tagged cells, the increased PKM{zeta} expression persists in dendritic compartments within stratum radiatum for 1 month, indicating the long-term storage of information in the CA3-to-CA1 pathway during remote spatial memory. We conclude that persistent increases in PKM{zeta} trace the molecular mechanism of LTP maintenance and thus the sites of information storage within brain circuitry during long-term memory.

neuroscience↗

bioRxiv2019

Optogenetic reactivation of prefrontal social memory trace mimics social buffering of fear

Social buffering occurs when the presence of a companion attenuates the physiological and/or behavioral effects of a stressful or fear-provoking event. It represents a way in which social interactions can immediately and potently modulate behavior. As such, social buffering is one mechanism by which strong social support increases resilience to mental illness. While the behavioral and neuroendocrine impacts of social buffering are well studied in multiple species, including humans, the neuronal bases of this behavioral phenomenon remain largely unexplored. Previous work has shown that the infralimbic prefrontal cortex (IL-PFC) is important for processing social information and, in separate studies, for modulating fear and anxiety. Thus, we hypothesized that socially-active cells within the IL-PFC may integrate social information to modulate fear responsivity. To test this hypothesis, we employed social buffering paradigms in male and female mice. Similar to prior studies in rats, we found that the presence of a cagemate reduced freezing in fear and anxiety-provoking contexts. In accordance with previous work, we demonstrated that interaction with a novel or familiar conspecific induces activity in the IL-PFC as evidenced by increased immediate early gene (IEG) expression. We then utilized an activity-dependent tagging murine line, the ArcCreERT2 mice, to express channelrhodopsin (ChR2) in neurons active during the social encoding of a new cagemate. We found that optogenetic reactivation of these socially-active neuronal ensembles phenocopied the effects of cagemate presence in male and female mice in learned and innate fear contexts without being inherently rewarding or altering locomotion. These data suggest that a social neuronal ensemble within the IL-PFC may contribute to social buffering of fear. These neurons may represent a novel therapeutic target for fear and anxiety disorders.

neuroscience↗

bioRxiv2019

Ovarian hormones mediate the prophylactic efficacy of (R,S)-ketamine and (2R,6R)-hydroxynorketamine in female mice

BACKGROUNDFemales are more likely than males to develop major depressive disorder (MDD) after exposure to stress. We previously reported that the administration of (R,S)-ketamine before stress can prevent stress-induced depressive-like behavior in male mice but have yet to assess efficacy in female mice or for other compounds, such as the metabolites of (R,S)-ketamine.\n\nMETHODSWe administered (R,S)-ketamine or its metabolites (2R,6R)-hydroxynorketamine ((2R,6R)-HNK) and (2S,6S)-HNK at various doses 1 week before one of a number of stressors, including contextual fear conditioning (CFC), learned helplessness (LH), and chronic immobilization stress (CIS), in male and female 129S6/SvEv mice. To examine the interaction between ovarian hormones and stress resilience, female mice also underwent ovariectomy surgery (OVX) and a hormone replacement protocol prior to drug administration.\n\nRESULTS(R,S)-ketamine and (2S,6S)-HNK, but not (2R,6R)-HNK, attenuated learned fear in male mice. (R,S)-ketamine and (2R,6R)-HNK, but not (2S,6S)-HNK, significantly reduced stress-induced depressive-like behavior in male and female mice. (R,S)-ketamine and (2R,6R)-HNK) were prophylactically effective at a lower dose (10 mg/kg and 0.025 mg/kg, respectively) in female mice than in male mice (30 mg/kg and 0.075 mg/kg, respectively). Moreover, ovarian-derived hormones were necessary and sufficient for prophylaxis in female mice.\n\nCONCLUSIONSOur results suggest that prophylactics against stress-induced depressive-like behavior can be developed in a sex-specific manner and that ovarian hormones mediate prophylactic efficacy in females. To our knowledge, this is the first demonstration of the prophylactic efficacy of the metabolites of (R,S)-ketamine in male and female mice.

neuroscience↗

bioRxiv2019

Prophylactic efficacy of 5-HT4R agonists against stress

Enhancing stress resilience could protect against stress-induced psychiatric disorders in at-risk populations. We and others have previously reported that (R,S)-ketamine acts as a resilience enhancing drug (e.g., prophylactic) against stress when administered 1 week before stress. While we have shown that the selective 5-hydroxytryptamine (5-HT) (serotonin) reuptake inhibitor (SSRI) fluoxetine (Flx) is ineffective as a prophylactic, it remains to be determined if other serotonergic drugs could be effective prophylactics. Here, we hypothesized that serotonin 4 receptor (5-HT4R) agonists could be prophylactic against fear, depressive-like, and/or anxiety-like behavior. We tested if three 5-HT4R agonists with varying affinity (e.g., partial or selective agonists) could protect against stress in two mouse strains by utilizing a chronic corticosterone (CORT) administration or a contextual fear conditioning (CFC) paradigm. Mice were administered RS-67,333, prucalopride, or PF-04995274 at varying doses and then 1 week later were subjected to chronic CORT or CFC. Chronic administration of RS-67,333, but not Flx was efficacious as a prophylactic against CORT in C57BL/6NTac mice. A single injection of RS-67,333 attenuated learned fear in male, but not female 129S6/SvEv mice. RS-67,333 was ineffective against stress-induced depressive-like behavior in the forced swim test (FST). A single injection of either prucalopride or PF-04995274 attenuated learned fear and decreased stress-induced depressive-like behavior. These data show that in addition to (R,S)-ketamine, 5-HT4R agonists are also effective prophylactics against stress, suggesting that the 5-HT4R may be a novel target for prophylactic drug development.

neuroscience↗