Hebrew University Study Reveals How Serotonin Signaling Is Hijacked in Brain's Striatum for Learning and Movement

Hebrew University Researchers Uncover Serotonin 'Hijacking' Mechanism in the Brain

A groundbreaking study from the Hebrew University of Jerusalem has revealed a fascinating new way the brain coordinates its chemical signals. Researchers discovered that in the striatum—a key brain region involved in learning, reward processing, and voluntary movement—acetylcholine (ACh), a neurotransmitter released by cholinergic interneurons (CINs), can directly 'hijack' serotonin (5-HT) signaling. This process allows for precise, synchronized release of serotonin, extending its influence across a wider area than normal.

The findings, published on March 16, 2026, in the prestigious journal Nature Communications (DOI: 10.1038/s41467-026-70359-6), challenge traditional views of neurotransmitter independence. Instead, they show how one system can commandeer another to fine-tune behavior, with profound implications for understanding disorders like obsessive-compulsive disorder (OCD) and depression.

The Striatum: Brain's Control Center for Action and Habit

The striatum, part of the basal ganglia, acts as the brain's hub for integrating sensory inputs, motivation, and motor control. Divided into dorsal (upper) and ventral (lower) parts, the dorsal striatum is particularly crucial for habit formation, goal-directed learning, and smooth movement execution. Disruptions here are linked to conditions ranging from Parkinson's disease to addiction.

Serotonin, often called the 'mood molecule,' modulates these functions by influencing neuronal excitability and synaptic plasticity. Acetylcholine, meanwhile, serves as a 'conductor,' synchronizing activity among striatal neurons. Prior research showed ACh triggering dopamine release via nicotinic acetylcholine receptors (nAChRs) on dopamine axons, but its role with serotonin was unknown—until now.

How the 'Hijacking' Works: A Step-by-Step Breakdown

The Hebrew University team, led by Prof. Joshua A. Goldberg from the Edmond and Lily Safra Center for Brain Sciences (ELSC) and Prof. Joshua L. Plotkin from Stony Brook University, used cutting-edge techniques to uncover the mechanism.

• Synchronous CIN Activation: When CINs fire together in bursts—mimicking natural behavioral events like decision-making—they release ACh.
• nAChR Binding: ACh binds to α4β2 nAChRs on nearby serotonergic axons (fibers from raphe nuclei).
• Serotonin Release: This depolarizes the axons, causing vesicular 5-HT exocytosis. The result? A ~45% expansion in serotonin's spatial reach (from 126 µm to 183 µm, per Lorentzian modeling).
• Regional Specificity: Exclusive to dorsal striatum; ventral lacks this coupling despite denser 5-HT innervation, possibly due to CIN density or receptor differences.

Methods included optogenetics (light-activated ChR2 in CINs), GRAB-5HT sensors for real-time 5-HT imaging via two-photon microscopy, and pharmacological blockers like mecamylamine to confirm nAChR dependency.

Experimental Evidence: From Mouse Brains to Behavioral Insights

In acute brain slices from mice expressing GRAB-5HT sensors, electrical stimulation (10 pulses at 10 Hz) or blue light flashes evoked 5-HT transients. nAChR antagonists reduced peak amplitude and shortened spread, proving direct axonal activation independent of GABA, glutamate, or muscarinic receptors.

In Sapap3^-/- mice—a validated OCD model with compulsive grooming—the hypercholinergic state amplified nAChR-dependent 5-HT (and dopamine) release by 2-3 fold, without changing baseline capacity. This 'overdrive' mirrors human OCD, where striatal hyperactivity drives compulsions.

Implications for Learning and Movement Control

The striatum's role in reinforcement learning relies on balanced dopamine-serotonin interplay. Dopamine signals rewards; serotonin brakes impulsivity and promotes patience. ACh-orchestrated 5-HT surges could refine action selection, stabilizing habits while preventing perseveration.

For movement, coordinated release ensures fluid execution. Dysregulation might contribute to Parkinson's dyskinesia, where levodopa excess from 5-HT terminals exacerbates involuntary motions amid cholinergic loss.

Statistics highlight stakes: Globally, 1 in 100 suffer OCD; depression affects 280 million. Understanding crosstalk offers targeted therapies beyond SSRIs, which boost extracellular 5-HT but ignore upstream drivers.

Photo by Shawn Day on Unsplash

Linking to Psychiatric Disorders: OCD and Beyond

OCD involves cortico-striatal loops with cholinergic hyperactivity. The study shows how CIN overfiring 'hijacks' 5-HT, flooding circuits and locking compulsions. In depression, low striatal 5-HT ties to anhedonia; disrupted coordination might underlie treatment resistance.

Quotes from lead authors: “Our findings show that the brain’s internal wiring allows one chemical system to take the wheel of another... In OCD, this coordination may go into overdrive.” This shifts paradigms from isolated imbalances to system failures. Future drugs modulating CINs or nAChRs could restore balance. For more on OCD models, see the Sapap3 data in the paper.

Hebrew University's Role in Neuroscience Excellence

The Edmond J. Safra Center for Brain Sciences at Hebrew University is a global leader in neural circuits. Prof. Goldberg's lab pioneered CIN-dopamine links; this extends to serotonin. Collaborations with Stony Brook underscore international impact.

Israel's higher ed invests heavily in brain research, with HUJI ranking top in neuroscience outputs. This study exemplifies how university labs drive discoveries with clinical promise, training PhDs like Lior Matityahu in optogenetics.

Explore neuroscience careers at AcademicJobs.com/research-jobs.

Broader Neuroscience Context and Related Research

Prior work showed CINs extending dopamine range; now serotonin joins, suggesting a general 'amplifier' role. Serotonin fine-tunes plasticity: High levels inhibit; low promote LTP for learning.

In Parkinson's, cholinergic denervation worsens; boosting CINs might aid therapy. Depression links to raphe hypoactivity, but striatal hijacking offers a local lens.

Future Directions: Therapeutic Horizons

Challenges: In vivo validation needed; CIN synchrony during behavior unclear. Opportunities: nAChR modulators for OCD; CIN-targeted DBS for movement disorders.

Timeline: Preclinical trials 2-5 years; clinical 5-10. Hebrew University plans behavioral assays linking CIN-5HT to compulsions.

Stakeholders: Patients (OCD affects 2-3% globally), pharma (beyond SSRIs), neuroscientists seeking circuit models.

Why This Matters for Higher Education and Research Careers

Studies like this highlight university labs' role in transformative science. Hebrew University's interdisciplinary approach—combining optogenetics, imaging, genetics—attracts top talent.

For aspiring researchers, skills in viral vectors, sensors, mouse models are gold. Global demand surges; neuroscience jobs up 15% yearly per BLS.

Actionable: Pursue PhDs in neural circuits; check faculty positions.

Photo by Aakash Dhage on Unsplash

Expert Perspectives and Global Reception

Neuroscience News hailed it as reframing 'chemical imbalances.' EurekAlert noted OCD surge potential. No X trends yet, but academic buzz high.

Balanced view: Exciting, but translation hurdles remain. Multi-perspective: Clinicians eye therapies; theorists model circuits.