Biology subjects

Malenka, R. C.

Publications and source records attributed to Malenka, R. C..

At least 19 recordsLinked to original sources

bioRxiv2026

Local control of dopamine release in nucleus accumbens gates opioid withdrawal aversion

The opioid crisis has emphasized the need for more effective treatments for opioid use disorder (OUD)1-3, which is characterized by habitual opioid use to avoid withdrawal symptoms4,5. Both physical and affective symptoms contribute to opioid withdrawal yet whether different neural mechanisms mediate these different symptom domains and contribute distinctly to opioid relapse is unknown. While neurons expressing mu opioid receptors (MORs) gate opioids reinforcing effects6-8 by increasing dopamine (DA) release in nucleus accumbens (NAc), sharp decreases in NAc DA release are associated with withdrawal9-11, the cellular and circuit mechanisms of which are unknown. Here we describe an unusual population of evolutionarily-conserved MOR+ neurons in the NAc expressing the transcription factor Tshz1. Increased activity in these neurons is required for withdrawal aversion learning. Deletion of MORs in Tshz1 neurons prevented withdrawal-induced decreases in DA release and affective aversion, but not physical symptoms associated with withdrawal. Pharmacological activation of mGluR8, which is preferentially expressed in Tshz1 neurons, reduced withdrawal aversion. Thus, by dissociating the circuit mechanisms contributing to the physical and affective components of opioid withdrawal focusing on the critical role of Tshz1 neurons, we have identified a novel druggable target with therapeutic potential for treating key OUD withdrawal symptoms.

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bioRxiv2025

Serotonergic neuron-glioma interactions drive high-grade glioma pathophysiology

High-grade gliomas are lethal brain cancers that are powerfully regulated by glutamatergic neurons through activity-dependent paracrine factors and functional neuron-to-glioma synapses. Here, we report that serotonergic neurons promote the proliferation of high-grade gliomas throughout the brain. Serotonergic neuronal activity drives circuit-specific increases in high-grade glioma proliferation, calcium transients, and reduced survival. This growth-promoting effect is chiefly mediated by activation of the serotonin (5-hydroxytryptamine; 5HT) receptor 5HT2A on glioma cells. Knock out or pharmacological blockade of 5HT2A receptors in glioma abrogated the glioma growth-promoting effects of serotonergic neuronal activity, while serotonergic psychedelic drugs robustly promote malignant cell proliferation. Gliomas alter serotonergic neuronal activity patterns, resulting in elevated serotonin release into the tumor microenvironment. Together, these findings uncover pathogenic, feed-forward interactions between serotonergic neurons and glioma cells.

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bioRxiv2025

Serotonin modulates nucleus accumbens circuits to suppress aggression

Serotonin (5-hydroxytryptamine; 5HT) has long been considered anti-aggressive, but the mechanisms by which 5HT regulates downstream circuits to control aggression remain unclear. Combining fiber photometry, optogenetics, and miniaturized microscope recordings in double-transgenic mice, we find that 5HT levels ramp up in the nucleus accumbens during aggression, inhibiting a subset of D1 medium spiny neurons to suppress attacks. Our results reveal a novel 5HT-mediated neuromodulatory mechanism for limiting aggressive behavior.

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bioRxiv2025

Psilocybin has no immediate or persistent analgesic effect in acute and chronic mouse pain models

The psychedelic psilocybin may have lasting therapeutic effects for patients with chronic pain syndromes. Some clinical and preclinical data suggest these putative benefits derive from direct analgesic effects. However, this possibility has not been comprehensively tested in preclinical models. Here, we show that psilocybin is not analgesic over a range of doses across multiple pain assays and models of acute and chronic inflammatory, neuropathic, or musculoskeletal pain in mice.

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bioRxiv2025

Cholinergic modulation of dopamine release drives effortful behavior

Effort is costly: given a choice, we tend to avoid it1. But in many cases, effort adds value to the ensuing rewards2. From ants3 to humans4, individuals prefer rewards that had been harder to achieve. This counterintuitive process may promote reward-seeking even in resource-poor environments, thus enhancing evolutionary fitness5. Despite its ubiquity, the neural mechanisms supporting this behavioral effect are poorly understood. Here we show that effort amplifies the dopamine response to an otherwise identical reward, and this amplification depends on local modulation of dopamine axons by acetylcholine. High-effort rewards evoke rapid acetylcholine release from local interneurons in the nucleus accumbens. Acetylcholine then binds to nicotinic receptors on dopamine axon terminals to augment dopamine release when reward is delivered. Blocking the cholinergic modulation blunts dopamine release selectively in high-effort contexts, impairing effortful behavior while leaving low-effort reward consumption intact. These results reconcile in vitro studies, which have long demonstrated that acetylcholine can trigger dopamine release directly through dopamine axons6-11; with in vivo studies that failed to observe such modulation12-14, but did not examine high-effort contexts. Our findings uncover a mechanism that drives effortful behavior through context-dependent local interactions between acetylcholine and dopamine axons.

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bioRxiv2025

Opponent regulation of striatal output pathways by dopamine and serotonin

Classic theories propose opponent functions for striatal dopamine (DA) and serotonin (5-hydroxytryptamine; 5HT), with DA promoting approach and 5HT promoting patience or avoidance. How these neuromodulators regulate downstream circuits to achieve such antagonistic effects remains mysterious. Here, we mapped striatal 5HT receptor expression and recorded from genetically-identified striatal neurons to demonstrate that DA and 5HT selectively activate distinct populations of striatal neurons to exert opponent control over striatal output.

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bioRxiv2025

A multi-institutional investigation of psilocybin's effects on mouse behavior

Studies reporting novel therapeutic effects of psychedelic drugs are rapidly emerging. However, the reproducibility and reliability of these findings could remain uncertain for years. Here, we implemented a multi-institutional collaborative approach to define the robust and replicable effects of the psychedelic drug psilocybin on mouse behavior. Five laboratories performed the same experiments to test the acute and persistent effects of psilocybin (2 mg/kg, IP) on various behaviors that psychedelics have been proposed to affect, including anxiety-related approach-avoidance, exploration, sociability, depression-related behaviors, fear extinction, and social reward learning. Through this coordinated approach, we found that psilocybin had several robust and replicable acute effects on mouse behavior, including increased anxiety- and avoidance-related behaviors and decreased fear expression. Surprisingly, however, we found that psilocybin did not have replicable effects 24 hours post psilocybin administration on reducing anxiety- and depression-like behaviors or facilitating fear extinction learning. Additionally, we were unable to observe psilocybin-induced alterations in social preference or social reward learning. Overall, our comprehensive characterization of psilocybins acute and persistent behavioral effects using [~]200 total male and female mice per experiment spread across five independent labs demonstrates with unique certainty several acute drug effects and suggests that psilocybins persistent effects in mice may be more modest and inconsistent than previously suggested. We believe this unusual multi-laboratory, highly coordinated research effort serves as a model for facilitating the generation of replicable results and consequently will reduce efforts based on unreliable and spurious results.

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bioRxiv2024

5-HT2C receptors in the nucleus accumbens constrain the rewarding effects of MDMA

MDMA is a promising adjunct to psychotherapy and has well-known abuse liability, although less than other amphetamine analogs. While the reinforcing dopamine (DA)-releasing properties of MDMA are on par with methamphetamine (METH), MDMA is a far more potent serotonin (5-HT) releaser, via the 5-HT transporter (SERT). MDMA-mediated 5-HT release in a major reward center, the nucleus accumbens (NAc), drives prosocial behaviors via 5-HT1BR activation. We hypothesized that this prosocial mechanism contributes to the reduced reinforcing properties of MDMA compared to METH and used a platform of assays to predict the balance of prosocial and abuse-linked effects of (R)-MDMA, a novel entactogen in clinical development. NAc DA release, measured by GRAB-DA photometry in vivo, increased in proportion to MDMA (7.5 and 15 mg/kg, i.p.) and METH (2 mg/kg i.p.)-conditioned place preference (CPP). Using conditional knockouts (cKOs) for DAT and SERT, microdialysis, and photometry, we found that MDMA-released 5-HT limited MDMA-released DA through actions in the NAc, rather than at ventral tegmental area DAergic cell bodies. SERT cKO reduced the MDMA dose required for CPP three-fold. This enhanced MDMA-CPP and increased DA release were replicated by intra-NAc infusion of either a 5-HT reuptake inhibitor (escitalopram) to prevent MDMA interaction with SERT, or a 5-HT2CR antagonist (SB242084), but not by the 5-HT1BR antagonist NAS-181. These data support separate mechanisms for the low abuse potential versus prosocial effect of MDMA. Using this platform of assays, (R)-MDMA is predicted to have prosocial effects and low abuse potential.

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bioRxiv2024

Cross-species brain-wide mapping reveals a conserved and coordinated network engaged by NAc DBS

SummaryNucleus accumbens (NAc) deep brain stimulation (DBS) has been increasingly explored as a treatment modality for refractory neuropsychiatric disorders. Uncovering the accumbens network that is engaged by DBS is a critical step forward in understanding how modulating this important node impacts the broader mesocorticolimbic circuit. Using whole-brain clearing and unbiased, brain-wide neural activity mapping, we found that NAc DBS increases neural activity in a coordinated mesocorticolimbic network in mice. Simultaneous intracranial electrophysiology recordings from the human NAc and brief stimulation epochs of homologous mesocorticolimbic nodes revealed similar connectivity. Altogether, these results identify specific connectivity conserved across species within the mesocorticolimbic circuit that may underlie mechanisms of NAc DBS.

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bioRxiv2024

Opioid receptor expressing neurons of the central amygdala gate behavioral effects of ketamine in mice

Ketamine has anesthetic, analgesic, and antidepressant properties which may involve multiple neuromodulatory systems. In humans, the opioid receptor (OR) antagonist naltrexone blocks the antidepressant effect of ketamine. It is unclear whether naltrexone blocks a direct effect of ketamine at ORs, or whether normal functioning of the OR system is required to realize the full antidepressant effects of treatment. In mice, the effect of ketamine on locomotion, but not analgesia or the forced swim test, was sensitive to naltrexone and was therefore used as a behavioral readout to localize the effect of naltrexone in the brain. We performed whole-brain imaging of cFos expression in ketamine-treated mice, pretreated with naltrexone or vehicle, and identified the central amygdala (CeA) as the area with greatest difference in cFos intensity. CeA neurons expressing both {micro}OR (MOR) and PKC{delta} were strongly activated by naltrexone but not ketamine, and selectively interrupting MOR function in the CeA either pharmacologically or genetically blocked the locomotor effects of ketamine. These data suggest that MORs expressed in CeA neurons gate behavioral effects of ketamine but are not direct targets of ketamine.

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bioRxiv2024

Intercalated amygdala dysfunction drives extinction deficits in the Sapap3 mouse model of obsessive-compulsive disorder

BackgroundThe avoidance of aversive stimuli due to negative reinforcement learning is critical for survival in real-world environments, which demand dynamic responding to both positive and negative stimuli that often conflict with each other. Individuals with obsessive-compulsive disorder (OCD) commonly exhibit impaired negative reinforcement and extinction, perhaps involving deficits in amygdala functioning. An amygdala subregion of particular interest is the intercalated nuclei of the amygdala (ITC) which has been linked to negative reinforcement and extinction, with distinct clusters mediating separate aspects of behavior. This study focuses on the dorsal ITC cluster (ITCd) and its role in negative reinforcement during a complex behavior that models real-world dynamic decision making. MethodsWe investigated the impact of ITCd function on negative reinforcement and extinction by applying fiber photometry measurement of GCamp6f signals and optogenetic manipulations during a platform-mediated avoidance task in a mouse model of OCD-like behavior: the Sapap3-null mouse. ResultsWe find impaired neural activity in the ITCd of male and female Sapap3-null mice to the encoding of negative stimuli during platform-mediated avoidance. Sapap3-null mice also exhibit deficits in extinction of avoidant behavior, which is modulated by ITCd neural activity. ConclusionsSapap3-null mice fail to extinguish avoidant behavior in platform-mediated avoidance, due to heightened ITCd activity. This deficit can be rescued by optogenetically inhibiting ITCd during extinction. Together, our results provide insight into the neural mechanisms underpinning negative reinforcement deficits in the context of OCD, emphasizing the necessity of ITCd in responding to negative stimuli in complex environments.

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bioRxiv2023

Striatal integration of inverse dopamine and serotonin signals gates learning

The neuromodulators dopamine (DA) and serotonin (5-hydroxytryptamine; 5HT) are powerful regulators of associative learning1-9. Similarities in the activity and connectivity of these neuromodulatory systems have inspired competing models of how DA and 5HT interact to drive the formation of new associations10-13. However, these hypotheses have yet to be tested directly because it has not been possible to precisely interrogate and manipulate multiple neuromodulatory systems in a single subject. Here, we establish a double transgenic mouse model enabling simultaneous genetic access to the brains DA and 5HT systems. Anterograde axon tracing revealed the nucleus accumbens (NAc) to be a putative hotspot for the integration of convergent DA and 5HT signals. Simultaneous recordings of DA and 5HT input activity in the NAc posterior medial shell revealed that DA axons are excited by rewards while 5HT axons are inhibited. Optogenetically blunting DA and 5HT reward responses simultaneously blocked learning about a reward-predictive cue. Optogenetically reproducing both DA and 5HT responses to reward, but not either one alone, was sufficient to drive the acquisition of new associations. Altogether, these results demonstrate that striatal integration of inverse DA and 5HT signals is a crucial mechanism gating associative learning.

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bioRxiv2023

UNRAVELing the synergistic effects of psilocybin and environment on brain-wide immediate early gene expression in mice

The effects of context on the subjective experience of serotonergic psychedelics have not been fully examined in human neuroimaging studies, partly due to limitations of the imaging environment. Here, we administered saline or psilocybin to mice in their home cage or an enriched environment, immunofluorescently-labeled brain-wide c-Fos, and imaged cleared tissue with light sheet microscopy to examine the impact of context on psilocybin-elicited neural activity at cellular resolution. Voxel-wise analysis of c-Fos-immunofluorescence revealed differential neural activity, which we validated with c-Fos+ cell density measurements. Psilocybin increased c-Fos expression in the neocortex, caudoputamen, central amygdala, and parasubthalamic nucleus and decreased c-Fos in the hypothalamus, cortical amygdala, striatum, and pallidum. Main effects of context and psilocybin-treatment were robust, widespread, and spatially distinct, whereas interactions were surprisingly sparse.

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bioRxiv2022

Striatal dopamine integrates cost, benefit and motivation

Dopamine (DA) release in the ventral and dorsal striatum has been linked to reward processing and motivation, but there are longstanding controversies about whether DA release in these key target structures primarily reflects costs or benefits, and how these signals vary with motivation. Here we apply behavioral economic principles to generate demand curves for rewards while directly measuring DA release in the nucleus accumbens (NAc) and dorsolateral striatum (DLS) via a genetically-encoded sensor. By independently varying costs and benefits, we reveal that DA release in both structures incorporates reward magnitude and sunk cost. Surprisingly, motivation was inversely correlated with reward-evoked DA release; the higher the motivation for rewards the lower the reward-evoked DA release. These relationships between DA release, cost and motivation remained identical when we used optogenetic activation of striatal DA inputs as a reward. Our results reconcile previous disparate findings by demonstrating that during operant tasks, striatal DA release simultaneously encodes cost, benefit and motivation but in distinct manners over different time scales.

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bioRxiv2022

Myelin plasticity in ventral tegmental area is required for opioid reward

All drugs of abuse induce long-lasting changes in synaptic transmission and neural circuit function that underlie substance use disorders. Here, we demonstrate that dopaminergic neuronal activity-regulated myelin plasticity is a key modulator of dopaminergic circuit function and opioid reward. Oligodendroglial lineage cells respond to dopaminergic neuronal activity evoked by either optogenetic stimulation or by morphine administration specifically within the reward center ventral tegmental area (VTA), but not along the axonal projections in the medial forebrain bundle nor within the target nucleus accumbens (NAc). Genetic blockade of oligodendrogenesis dampens NAc dopamine release dynamics, which is critical for reward learning, and impairs behavioral conditioning to morphine. Our findings identify dopaminergic neuronal activity-regulated myelin plasticity as an important circuit modification that is required for opioid reward. One-Sentence SummaryActivity-dependent myelin plasticity in the ventral tegmental area modulates dopaminergic circuit function and opioid reward

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bioRxiv2022

Somatodendritic release of cholecystokinin potentiates GABAergic synapses onto ventral tegmental area dopamine cells

Neuropeptides are contained in nearly every neuron in the central nervous system and can be released from somatodendritic sites as well as from nerve terminals. Cholecystokinin (CCK), among the most abundant neuropeptides in the brain, is expressed in the majority of midbrain dopamine neurons. Here we report that ventral tegmental area (VTA) dopamine neurons release CCK from somatodendritic regions, where it triggers long-term potentiation of GABAergic synapses. The somatodendritic release occurs with trains of action potentials or prolonged but modest depolarization and is dependent on synaptotagmin 7 and T-type Ca2+ channels. Depolarization-induced LTP is blocked by the CCK2R antagonist, LY225910, and mimicked by exogenously added CCK. To test the behavioral role of CCK, we infused it into the mouse VTA. Ca2+ imaging in vivo demonstrated that infused CCK reduced dopamine cell signals during fasted food consumption. Moreover, local infusion of CCK also inhibited food consumption and decreased distance traveled in an open field test. Together our experiments introduce somatodendritic neuropeptide release as a previously unknown feedback regulator of VTA dopamine cell excitability and dopamine-related behaviors.

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bioRxiv2020

A molecular calcium integrator reveals a striatal cell-type driving aversion

The ability to record transient cellular events in the DNA or RNA of cells would enable precise, large-scale analysis, selection, and reprogramming of heterogeneous cell populations. Here we report a molecular technology for stable genetic tagging of cells that exhibit activity-related increases in intracellular calcium concentration (FLiCRE). We used FLiCRE to transcriptionally label activated neural ensembles in the nucleus accumbens of the mouse brain during brief stimulation of aversive inputs. Using single-cell RNA sequencing, we detected FLiCRE transcripts among the endogenous transcriptome, providing simultaneous readout of both cell-type and calcium activation history. We identified a cell-type in the nucleus accumbens activated downstream of long-range excitatory projections. Taking advantage of FLiCREs modular design, we expressed an optogenetic channel selectively in this cell-type, and showed that direct recruitment of this otherwise genetically-inaccessible population elicits behavioral aversion. The specificity and minute-resolution of FLiCRE enables molecularly-informed characterization, manipulation, and reprogramming of activated cellular ensembles.

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bioRxiv2019

Distinct neural mechanisms for the prosocial and rewarding properties of MDMA

The extensively abused recreational drug MDMA has shown promise as an adjunct to psychotherapy for treatment-resistant psychiatric disease. It is unknown, however, whether the mechanisms underlying its prosocial therapeutic effects and abuse potential are distinct. We demonstrate in mice that MDMA acting at the serotonin transporter within the nucleus accumbens is necessary and sufficient for MDMAs prosocial effect. MDMAs acute rewarding properties, in contrast, require dopaminergic signaling. MDMAs prosocial effect requires 5-HT1b receptor activation and is mimicked by d-fenfluramine, a selective serotonin-releasing compound. By dissociating the mechanisms of MDMAs prosocial effects from its addictive properties, we provide evidence for a conserved neuronal pathway, which can be leveraged to develop novel therapeutics with limited abuse liability.\n\nOne Sentence SummaryMDMA, which has both therapeutic and abuse potential, engages a brain region-specific serotonergic pathway to produce its prosocial effect.

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