Biology subjects

Creed, M. C.

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

15 recordsLinked to original sources

bioRxiv2026

FLEX-DBS: a flexible wireless platform for bilateral constant-current deep brain stimulation in freely moving rodents

Background: Preclinical deep brain stimulation (DBS) in rodents is central to understanding how DBS works, but most rodent DBS is delivered through a tether, which constrains behavior, home-cage experiments and uninterrupted stimulation. Most long-runtime wireless mouse stimulators achieve their runtimes by setting stimulation parameters before or around implantation and operating from supplies of about 3 V. New method: FLEX-DBS (Flexible Deep Brain Stimulation) is a head-mounted, battery-powered stimulator that delivers bilateral constant-current stimulation from improved Howland current pumps on +/-5 V rails. Amplitude, pulse width and frequency are programmable in continuous and burst modes from an iOS application over Bluetooth Low Energy, and stimulation continues autonomously after the phone disconnects. The device measures 19.5 x 22.5 x 8.72 mm, weighs 3.71 g in operation and runs on two size-13 zinc-air cells, which are exchanged by briefly detaching the device, pausing stimulation only for the exchange. Results: Into a 1 k{Omega} bench load, delivered current increased approximately linearly with the amplitude setting and was repeatable from pulse to pulse, with an asymmetric biphasic waveform whose recovery phase ran at about one fifth of the stimulating amplitude. Battery current was 1.47-1.89 mA in standby and 3.15-3.42 mA during stimulation at amplitude settings of 60-400 A, giving a projected three days of continuous stimulation per pair of cells. Firmware v0.5 left a net charge of 26-35 % of the stimulating-phase charge per pulse into 1 k{Omega}. Into 47 k{Omega}, within the in vivo load range, stimulating current was compliance-limited at 93 A. Pulse-derived estimates of the effective load presented by five implanted platinum electrodes in three mice had weekly means of 43-54 k{Omega} over eight weeks (32-80 k{Omega} across individual sessions), placing the maximum regulated current near 90 A (81-101 A at the weekly means). Analysis of the current-pump network bounds load-dependent current error at 3-8% for these loads. In vivo, we delivered cingulate FLEX-DBS at high amplitude settings intended to evoke a robust stimulation-associated behavioral phenotype in six mice. Time spent immobile in an open field rose from 46.5% at baseline to 75.7% during stimulation (a 62.7% increase in the group mean) and remained elevated after stimulation ended; without a sham control, this increase cannot be separated from within-session habituation. Comparison with existing methods: Among the published wireless rodent stimulators compared here, several offer some of these capabilities, but none combines bilateral constant current output, real-time wireless control that continues as autonomous stimulation after disconnect, and both continuous and burst modes; FLEX-DBS does so at the cost of runtime measured in days rather than weeks. Conclusions: FLEX-DBS is designed for untethered DBS experiments in which parameters must be set, changed and verified at the cage. Its measured power consumption permits a projected three days of continuous operation per cell pair; firmware v0.5 requires improved charge balancing before prolonged in vivo stimulation. The electrode load, rather than the programmable range, sets the usable stimulation amplitude in vivo. In vivo, stimulation at high amplitude settings was associated with increased immobility, consistent with effective stimulation through implanted electrodes; electrode impedance and delivered current were not measured in these mice.

bioengineering↗

bioRxiv2026

PixelPaws: a low-cost, open-source integrated platform for automated scoring of mouse behaviors

Behavioral scoring is central to preclinical pain research but is typically performed manually, which is inherently low-throughput and subject to variability between observers. Automated alternatives exist, but cost and programming expertise limit adoption beyond the laboratories that build them. Here we describe PixelPaws, an open-source platform combining a near-infrared imaging enclosure built from consumer parts for under $300, multi-camera acquisition software, a bundled pose-estimation network, and eight classifiers in a graphical user interface. We evaluated the platform across standard assays of pain, itch, and opioid withdrawal. Licking, scratching, and jumping classifiers were validated against trained human observers by leave-one-session-out evaluation. In the formalin assay, classifier-scored licking followed the expected biphasic time course and was reduced dose-dependently by oxycodone, with a phase 2 potency estimate comparable to blinded manual scoring. Chloroquine roughly tripled scratching, and naloxone precipitated a burst of jumping in oxycodone-treated mice. From the same recordings we derived a set of paw contour metrics. Contour intensity fell after formalin and tracked the oxycodone dose series, and contour area shifted toward symmetry after oxycodone in nerve-injured mice. Behavioral sequencing revealed distinct changes in the transi

neuroscience↗

bioRxiv2026

Ventral pallidal GABAergic neurons control hedonic feeding and obesity

Food intake is governed by two interacting drives. The homeostatic hunger drive regulates food intake to fulfill caloric needs while the hedonic drive promotes intake of palatable foods outside of caloric need. It is unclear which neural substrates can control the hedonic drive and thereby reduce overeating of palatable foods and associated obesity. Here, we show that ventral pallidal GABAergic neurons (VPGABA) preferentially control hedonic feeding and are necessary for diet-induced obesity in mice. Stimulating VPGABA neurons drove robust consumption of high-fat diet and liquids, but not regular laboratory chow. Despite driving intake of palatable foods, VPGABA neurons are relatively insensitive to homeostatic signals - they express few hunger-hormone receptors and are not activated by ghrelin administration or fasting. Single-cell calcium imaging revealed stronger engagement of VPGABA neurons during long vs short feeding bouts, suggesting control over bout duration, which has been linked to palatability. This was confirmed with closed-loop optogenetic stimulation. Finally, taCasp3-mediated ablation of VPGABA neurons reduced intake of palatable liquids and blocked high-fat diet-induced obesity without impacting homeostatic feeding. Together, these findings establish VPGABA neurons as a neural population that preferentially controls hedonic over homeostatic feeding and can be leveraged to block obesity in mice.

neuroscience↗

bioRxiv2026

Sex differences in exploration-exploitation strategies during home-cage decision making

The exploration-exploitation trade-off refers to the conflict between using known strategies that reliably yield reward (exploitation) and sampling uncertain options that might yield better outcomes (exploration). Dysregulation of this balance is implicated in neuropsychiatric disease, and while sex differences in this balance have been described, the biological bases remain unclear. To quantify sex differences in this trade-off, we tested mice (n=74 male, 62 female) on four home-cage based foraging tasks with an operant pellet dispensing device, Feeding Experimentation Device 3 (FED3). Mice completed the tasks continuously over multiple days and the tasks were their only source of food. Across multiple tasks, males showed higher win-stay behaviour than females, indicating greater exploitation of previously rewarded actions, an effect that was modest in size but highly significant. Power analyses revealed that >30 mice per sex were needed to detect these modest but significant sex differences with 80% power. No consistent sex differences were observed in pellet intake, suggesting that differences in exploitation did not reflect differences in hunger drive or demand for pellets. Exploitation is a more efficient strategy when environmental parameters are fixed, while exploration can be more advantageous when parameters such as reward locations are changing and uncertain. We tested this idea by re-running our mice in a probabilistic foraging task, where actions led to uncertain probabilities of reward. While males continued to show higher levels of win-stay behaviour on this task, this no longer led to increases in accuracy. Behavioural modelling also supported this framework, demonstrating that stronger win-stay behaviour was most advantageous in deterministic models, and less advantageous in probabilistic models. Together, our findings demonstrate that male and female mice have small but significant differences in their exploration-exploitation balance, which leads to more accurate foraging in certain, but not uncertain, environments.

neuroscience↗

bioRxiv2025

Inducible Calling Cards: Developing Mouse Reagents for Experimentally Controlled Transposon Insertion in vivo.

The piggyBac transposase enables robust forward genetic screens in mice. Further, fusions of piggyBac with specific transcription factors (TFs) enables recovery of recoverable transposons (Calling Cards) for recording location of DNA binding events in vitro and in vivo. Such applications would be enhanced by engineering inducible transposases, such that timing of recording could be precisely controlled in vivo, as has been previously developed in vitro. Here, we tested two approaches for applying inducible Calling Cards (iCC) in the murine brain. We engineered knock-ins of inducible versions of two TFs: Jun, an immediate early gene that serves as a proxy for neural activity, and Sp1, a promiscuous binder of CpG unmethylated regions that indicates active promoters. We fused hyperPiggyBac transposase and a tamoxifen-inducible domain (ERT2) to these TFs and tested the system for efficacy and temporal control of insertions, both in vitro and in vivo. Jun-iCC mice developed normally with no behavioral abnormalities, showed tamoxifen-dependent recording, and captured neural activity during pharmacologically induced seizures. Jun-iCC yields relatively low numbers of insertions, likely due to the transient expression of Jun. In contrast, Sp1-iCC provided substantially higher insertion numbers, but transgenic animals exhibited developmental abnormalities, including reduced viability, anophthalmia, and reduced body weight, suggesting that ERT2 domains may sequester Sp1 and thus significantly impact development. Nonetheless, these inducible Calling Cards mouse lines enable drug-inducible integration of transposon cargo into specific loci in the living mouse. SIGNIFICANCE STATEMENTTransposases, like the more widely used recombinases (Cre, Flp, etc.), enable the integration of a variety of DNA sequences into the genome, but without dependence on LoxP sites. However, few mouse reagents exist for transposases. Cre has been adapted to be drug-inducible, as well as activity-regulated (e.g., FOS-TRAP). Thus, additional applications would become available if transposases could also be drug-controlled and activity-dependent. Further, there may be benefits to targeting integration to specific genomic region types (e.g., promotors). Here, we report results testing mouse lines for two drug-inducible transposase fusions to transcription factors (TF) - the promoter binding SP1, and activity dependent Jun. Both allowed genomic integration, with viability, efficiency, inducibility and targeting varying by TF-fusion.

neuroscience↗

bioRxiv2025

Reduced SK channel control of mesolimbic dopamine neuron firing drives reward seeking adaptations in chronic pain

Patients with chronic neuropathic pain typically experience affective symptoms that drive reduced quality of life and negatively impact pain management. Mesolimbic dopamine is necessary for reward valuation and learning, and the existence of a hypodopaminergic state has been proposed to underlie these affective symptoms of chronic pain. However, direct functional evidence for this hypodopaminergic state is lacking, and the mechanisms underlying its emergence over the acute to chronic pain transition are unknown. Here, we find a selective deficit in the ability of mesolimbic dopamine neurons to sustain burst firing, which is apparent uniquely at chronic timepoints following neuropathic injury. As a result, animals are unable to sustain effortful pursuit of rewards under conditions of high effort or time costs. Convergent biophysical modeling and experimental electrophysiology establish that in a spared nerve injury (SNI) model of chronic neuropathic pain, calcium-activated, small-conductance potassium (SK) channel function is impaired, resulting in lower peak firing and earlier entry into depolarization block of mesolimbic dopamine neurons. Critically, dopamine dependent reward learning, formation of cue-reward associations and locomotor activity remain intact, arguing against the interpretation of a generalized hypodopaminergic state. These results elucidate a circuit-level basis for selective motivational deficits emerging in chronic neuropathic pain.

neuroscience↗

bioRxiv2025

Single-Cell Resolution of Individual Variation in Hypothalamic Neurons Allows Targeted Manipulation Affecting Social Motivation

Despite decades of research, connecting molecular and cellular phenotypes to complex behavioral traits remains an elusive goal1. Social motivation exhibits individual trait variation2, which we hypothesize is mediated by molecular and cellular variability across hypothalamic neurons. To test this, we generated single-nucleus RNA-sequencing profiles3,4 of >120,000 neurons from tuberal hypothalamus and adjacent thalamus in 36 mice, balanced across sex and autism-associated mutation5, with all mice assessed for social motivation2. First, we show that molecular activation patterns predict behavior across individuals: specifically, activation of paraventricular Agtr1a+ (angiotensin receptor 1a) neurons predicted reduced social behavior. Subsequent inhibition of AGTR1A with telmisartan--an FDA-approved antihypertensive6--improved social orienting. Second, we show natural variation in neuronal proportions--likely arising from stochastic developmental events7--is sufficient to shape adult behavior even among genetically-identical individuals: we identified multiple neuronal populations whose relative abundance predicted social reward-seeking behavior. Chemogenetic inhibition of one such population, Nxph4+ neurons of the postero-lateral hypothalamus8, suppressed multiple aspects of social motivation. This work establishes proof-of-principle for an approach where single-cell genomics precisely maps neural substrates governing behavior. This approach revealed that stochastic variations in neuronal architecture deterministically influence social motivation, and enabled identification of therapeutically-actionable targets with immediate translational potential for disorders with social deficits.

genetics↗

bioRxiv2024

Transcriptomic landscape of mammalian ventral pallidum at single-cell resolution

The ventral pallidum (VP) is critical for motivated behaviors. While contemporary work has begun to elucidate the functional diversity of VP neurons, the molecular heterogeneity underlying this functional diversity remains incompletely understood. We used snRNA-seq and in situ hybridization to define the transcriptional taxonomy of VP cell types in mice, macaques, and baboons. We found transcriptional conservation between all three species, within the broader neurochemical cell types. Unique dopaminoceptive and cholinergic subclusters were identified and conserved across both primate species but had no homolog in mice. This harmonized consensus VP cellular atlas will pave the way for understanding the structure and function of the VP and identified key neuropeptides, neurotransmitters, and neuro receptors that could be targeted within specific VP cell types for functional investigations. TeaserGenetic identity of ventral pallidum cell types is conserved across rodents and primates at the transcriptional level

neuroscience↗

bioRxiv2023

Impact of delta9-tetrahydrocannabinol and oxycodone co-administration on measures of antinociception, dependence, circadian activity, and reward in mice

Oxycodone is commonly prescribed for moderate to severe pain disorders. While efficacious, long-term use can result in tolerance, physical dependence, and the development of opioid use disorder. Cannabis and its derivatives such as {Delta}9-Tetrahydrocannabinol ({Delta}9-THC) have been reported to enhance oxycodone analgesia in animal models and in humans. However, it remains unclear if {Delta}9-THC may facilitate unwanted aspects of oxycodone intake, such as tolerance, dependence, and reward at analgesic doses. This study sought to evaluate the impact of co-administration of {Delta}9-THC and oxycodone across behavioral measures related to antinociception, dependence, circadian activity, and reward in both male and female mice. Oxycodone and {Delta}9-THC produced dose-dependent antinociceptive effects in the hotplate assay that were similar between sexes. Repeated treatment (twice daily for 5 days) resulted in antinociceptive tolerance. Combination treatment of oxycodone and {Delta}9-THC produced a greater antinociceptive effect than either administered alone, and delayed the development of antinociceptive tolerance. Repeated treatment with oxycodone produced physical dependence and alterations in circadian activity, neither of which were exacerbated by co-treatment with {Delta}9-THC. Combination treatment of oxycodone and {Delta}9-THC produced CPP when co-administered at doses that did not produce preference when administered alone. These data indicate that {Delta}9-THC may facilitate oxycodone-induced antinociception without augmenting certain unwanted features of opioid intake (e.g. dependence, circadian rhythm alterations). However, our findings also indicate that {Delta}9-THC may facilitate rewarding properties of oxycodone at therapeutically relevant doses which warrant consideration when evaluating this combination for its potential therapeutic utility.

neuroscience↗

bioRxiv2023

Cell specific single viral vector CRISPR/Cas9 editing and genetically encoded tool delivery in the central and peripheral nervous systems

Gene manipulation strategies using germline knockout, conditional knockout, and more recently CRISPR/Cas9 are crucial tools for advancing our understanding of the nervous system. However, traditional gene knockout approaches can be costly and time consuming, may lack cell-type specificity, and can induce germline recombination. Viral gene editing presents and an exciting alternative to more rapidly study genes of unknown function; however, current strategies to also manipulate or visualize edited cells are challenging due to the large size of Cas9 proteins and the limited packaging capacity of adeno-associated viruses (AAVs). To overcome these constraints, we have developed an alternative gene editing strategy using a single AAV vector and mouse lines that express Cre-dependent Cas9 to achieve efficient cell-type specific editing across the nervous system. Expressing Cre-dependent Cas9 in specific cell types in transgenic mouse lines affords more space to package guide RNAs for gene editing together with Cre-dependent, genetically encoded tools to manipulate, map, or monitor neurons using a single virus. We validated this strategy with three commonly used tools in neuroscience: ChRonos, a channelrhodopsin, for manipulating synaptic transmission using optogenetics; GCaMP8f for recording Ca2+ transients using fiber photometry, and mCherry for anatomical tracing of axonal projections. We tested these tools in multiple brain regions and cell types, including GABAergic neurons in the nucleus accumbens (NAc), glutamatergic neurons projecting from the ventral pallidum (VP) to the lateral habenula (LHb), dopaminergic neurons in the ventral tegmental area (VTA), and parvalbumin (PV)-positive proprioceptive neurons in the periphery. This flexible approach should be useful to identify novel genes that affect synaptic transmission, circuit activity, or morphology with a single viral injection.

neuroscience↗

bioRxiv2022

Neuropathic injury drives a generalized negative affective state in mice

Neuropathic pain causes both sensory and emotional maladaptation. Preclinical animal studies of neuropathic pain-induced negative affect could result in novel insights into the mechanisms of chronic pain. Modeling pain-induced negative affect, however, is variable across research groups and conditions. The same injury may or may not produce robust negative affective behavioral responses across different species, strains, and laboratories. Here we sought to identify negative affective consequences of the spared nerve injury model on C57BL/6J male and female mice. We found no significant effect of spared nerve injury across a variety of approach-avoidance, hedonic choice, and coping strategy assays. We hypothesized these inconsistencies may stem in part from the short test duration of these assays. To test this hypothesis, we used the homecage-based Feeding Experimentation Device version 3 to conduct 12-hour, overnight progressive ratio testing to determine whether mice with chronic spared nerve injury had decreased motivation to earn palatable food rewards. Our data demonstrate that despite equivalent task learning, spared nerve injury mice are less motivated to work for a sugar pellet than sham controls. Further, when we normalized behavioral responses across all the behavioral assays we tested, we found that a combined normalized behavioral score is predictive of injury-state and significantly correlates with mechanical thresholds. Together these results suggest that homecage-based operant behaviors provide a useful platform for modeling nerve injury-induced negative affect and that valuable pain-related information can arise from agglomerative data analyses across behavioral assays - even when individual inferential statistics do not demonstrate significant mean differences.

neuroscience↗

bioRxiv2022

Oral oxycodone self-administration leads to features of opioid addiction in male and female mice

Use of prescription opioids, particularly oxycodone is an initiating factor driving the current opioid epidemic. There are several challenges with modeling oxycodone abuse. First, prescription opioids including oxycodone are orally self-administered and have different pharmacokinetics and dynamics than morphine or fentanyl which have been more commonly used in rodent research. This oral route of administration determines the pharmacokinetic profile, which then influences the establishment of drug-reinforcement associations in animals. Moreover, the pattern of intake and the environment in which addictive drugs are self-administered are critical determinants of the levels of drug intake, of behavioral sensitization, and of propensity to relapse behavior. These are all important considerations when modeling prescription opioid use, which is characterized by continuous drug access in familiar environments. Thus, to model features of prescription opioid use and the transition to abuse, we designed an oral, homecage-based oxycodone self-administration paradigm. Mice voluntarily self-administer oxycodone in this paradigm without any taste modification such as sweeteners, and the majority exhibit preference for oxycodone, escalation of intake, physical signs of dependence, and reinstatement of seeking after withdrawal. In addition, a subset of animals demonstrate drug taking that is resistant to aversive consequences. This model is therefore translationally relevant and useful for studying the neurobiological substrates of prescription opioid abuse.

neuroscience↗

bioRxiv2022

Enhanced food motivation in obese mice is controlled by D1R expressing spiny projection neurons in the nucleus accumbens.

Obesity is a chronic relapsing disorder that is caused by an excess of caloric intake relative to energy expenditure. In addition to homeostatic feeding mechanisms, there is growing recognition of the involvement of food reward and motivation in the development of obesity. However, it remains unclear how brain circuits that control food reward and motivation are altered in obese animals. Here, we tested the hypothesis that signaling through pro-motivational circuits in the core of the nucleus accumbens (NAc) is enhanced in the obese state, leading to invigoration of food seeking. Using a novel behavioral assay that quantifies physical work during food seeking, we confirmed that obese mice work harder than lean mice to obtain food, consistent with an increase in the relative reinforcing value of food in the obese state. To explain this behavioral finding, we recorded neural activity in the NAc core with both in vivo electrophysiology and cell-type specific calcium fiber photometry. Here we observed greater activation of D1-receptor expressing NAc spiny projection neurons (NAc D1SPNs) during food seeking in obese mice relative to lean mice. With ex vivo slice physiology we identified both pre- and post-synaptic mechanisms that contribute to this enhancement in NAc D1SPN activity in obese mice. Finally, blocking synaptic transmission from D1SPNs decreased physical work during food seeking and attenuated high-fat diet-induced weight gain. These experiments demonstrate that obesity is associated with a selective increase in the activity of D1SPNs during food seeking, which enhances the vigor of food seeking. This work also establishes the necessity of D1SPNs in the development of diet-induced obesity, establishing these neurons as a potential therapeutic target for preventing obesity.

neuroscience↗

bioRxiv2021

Modeling features of addiction with an oral oxycodone self-administration paradigm

Prescription opioid use is an initiating factor driving the current opioid epidemic. There are several challenges with modeling prescription opioid addiction. First, prescription opioids such as oxycodone are orally self-administered and have different pharmacokinetics and dynamics than morphine or fentanyl. This oral route of administration determines the pharmacokinetic profile, which is critical for establishing reliable drug-reinforcement associations in animals. Moreover, the pattern of intake and environment in which addictive drugs are self-administered intake are critical determinants of the levels of drug intake, sensitization and relapse behavior. This is an important consideration with prescription opioid use, which is characterized by continuous drug access in familiar environments. Thus, to model features of prescription opioid use and the transition to abuse, we present an oral oxycodone self-administration paradigm that is administered in the home cage. Mice voluntarily self-administer oxycodone in this paradigm without any taste modification such as sweeteners, and exhibit preference for oxycodone, escalation of intake, physical signs of dependence, reinstatement of seeking after withdrawal, and a subset of animals demonstrate drug taking that is resistant to aversive consequences. This model could be useful for studying the neurobiological substrates specifically relevant to prescription opioid abuse.

neuroscience↗

bioRxiv2020

Ventral arkypallidal neurons modulate accumbal firing to promote reward consumption.

A pause in firing of nucleus accumbens shell (NAcSh) neurons is critical for reward consumption; however, the substrate driving this pause is unknown. While ventral pallidal (VP) activity encodes reward value, the specific roles of VP subpopulations in computation and expression of this value are poorly understood. Here, we establish that inhibitory input from the VP is crucial for reward-related inhibition of NAc firing. A sparse, non-canonical subpopulation of VP neurons, the so-called "ventral arkypallidal (vArky)" neurons makes inhibitory synaptic contacts throughout the NAcSh, and drives inhibition of NAcSh neurons in vivo. Moreover, endogenous calcium activity of vArky neurons predicted subsequent reward consumption behavior, while optogenetically activating this pathway increased reward consumption by amplifying hedonic value of reward. Classically, the VP is considered downstream of the NAc; however, our results challenge this view and establish that vArky neurons in the VP promote reward consumption via potent modulation of NAcSh firing.

neuroscience↗