Summary: Texas A&M researchers report that fentanyl increases activity of direct-pathway medium spiny neurons (dMSNs) in the striatum. During early withdrawal, these dMSNs send stronger inhibitory signals to downstream dopamine-producing neurons, creating a hypodopaminergic state that contributes to the negative emotions and anxiety seen in withdrawal. Suppressing dMSN activity reduced withdrawal symptoms and anxiety-like behaviors in experimental models, pointing to potential targets for treating opioid use disorder.
Source: Texas A&M
The opioid epidemic continues to devastate communities across the United States, with tens of thousands of opioid-related deaths annually. Although public health data highlight the scale of the crisis, the neural circuits that drive addiction, withdrawal-induced negative emotion, and relapse remain incompletely understood.
A new study in Cell Reports from Jun Wang, associate professor in the Department of Neuroscience and Experimental Therapeutics at Texas A&M University School of Medicine, and colleagues clarifies how fentanyl, a potent synthetic opioid, alters specific striatal circuits. The team focused on the striatum, a brain region central to voluntary actions, reward processing, and drug-seeking behavior.
Many individuals who stop using opioids relapse weeks or months later, often driven by the depression, anxiety and dysphoria that accompany withdrawal. Treatments that reduce these negative emotional states could substantially increase the chances of durable recovery from opioid use disorder.
Opioids exert much of their effect through μ-opioid receptors (MORs). In the striatum, MORs are expressed on a subset of neurons called direct-pathway medium spiny neurons (dMSNs), which promote “go” behaviors and have been implicated in drug-seeking. The striatum is organized into patch and matrix compartments; the patch compartment is enriched in MOR-expressing dMSNs and is heavily involved in emotional processing and decision-making.
The researchers examined how chronic opioid exposure and subsequent withdrawal alter activity in patch dMSNs and their outputs, with an emphasis on how those changes produce the negative affect that can trigger relapse.
Key findings show that fentanyl enhances dMSN activity in the striatum and, during early withdrawal, strengthens GABAergic (inhibitory) signaling from these dMSNs to downstream targets, including dopaminergic neurons in midbrain regions. Because dopaminergic neurons regulate motivation, reward and positive affect, their increased inhibition creates a hypodopaminergic state that likely underlies withdrawal-related anxiety and dysphoria.
The study demonstrates that repeated morphine or fentanyl exposure potentiates inhibitory striatal outputs to the globus pallidus and substantia nigra, and that fentanyl self-administration reduces midbrain dopamine neuron activity. Electrophysiological and behavioral experiments showed that these circuit changes are associated with increased anxiety-like behavior and conditioned responses to drug-associated contexts.
Importantly, targeted inhibition of striatal MOR-positive neurons—those dMSNs enriched in the patch compartment—reversed physical signs of withdrawal and reduced anxiety-like behaviors in the experimental models. These results indicate that the enhanced GABAergic transmission from dMSNs is not only correlated with negative affect but is functionally important for producing withdrawal symptoms.
By identifying specific striatal pathways that shift toward stronger inhibitory output and suppress dopaminergic signaling during withdrawal, this research points to new molecular and circuit-level targets for interventions. Therapies that normalize dMSN activity or the downstream inhibition of dopamine neurons could help alleviate the negative emotional states that drive relapse, improving recovery outcomes for people with opioid use disorder.
In short, the study advances understanding of how chronic opioid exposure and withdrawal remodel striatal circuits—particularly MOR-expressing dMSNs and their GABAergic projections—to produce hypodopaminergic states and negative affect. These mechanistic insights offer a foundation for developing treatments aimed at reducing withdrawal-related mood disturbances and preventing relapse.
About this opioid addiction research news
Author: Press Office
Source: Texas A&M
Contact: Press Office – Texas A&M
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Original Research: Open access.
“Striatal μ-opioid receptor activation triggers direct-pathway GABAergic plasticity and induces negative affect” by Wei Wang et al. Cell Reports
Abstract
Striatal μ-opioid receptor activation triggers direct-pathway GABAergic plasticity and induces negative affect
Highlights
- Repeated morphine and fentanyl injections potentiate inhibitory striatopallidal (dMSN→GPh) transmission
- Repeated fentanyl exposure enhances inhibitory striatonigral (dMSN→SNc) transmission
- Fentanyl recruits striatal neurons that encode contextual memory associated with drug exposure
- Striatal MOR-positive neurons drive the negative affect observed during fentanyl withdrawal
Summary
Withdrawal from chronic opioid use frequently produces a hypodopaminergic state and negative emotional symptoms that can precipitate relapse. Direct-pathway medium spiny neurons in the striatal patch compartment express μ-opioid receptors (MORs), but the ways in which chronic opioid exposure and withdrawal alter these neurons and their downstream outputs were not fully defined.
The study reports that acute MOR activation suppresses GABAergic striatopallidal transmission to habenula-projecting globus pallidus neurons. However, after repeated morphine or fentanyl exposure, withdrawal potentiates this GABAergic transmission. Intravenous fentanyl self-administration also enhanced striatonigral inhibitory transmission and diminished midbrain dopaminergic activity.
Fentanyl-activated striatal neurons were necessary for retrieving contextual memories in conditioned place preference assays, and chemogenetic inhibition of striatal MOR-positive neurons alleviated both physical withdrawal signs and anxiety-like behaviors. Together, these results indicate that chronic opioid use induces GABAergic plasticity in striatopallidal and striatonigral pathways, producing a hypodopaminergic state that contributes to negative affect and may promote relapse.