---
title: "Whole-Brain Activation Patterns After Mu Opioid and NOP Receptor Agonism Reveal Regional and Netwo"
id: "biorxiv-4-whole-brain-cellular-activation-after-mu-and-nop-receptor-agonism-identifies"
canonical_url: "https://medichelpline.com/clinical-feed/biorxiv-4-whole-brain-cellular-activation-after-mu-and-nop-receptor-agonism-identifies"
content_type: "clinical_feed_article"
specialty: "Pharmacology"
source_name: "bioRxiv (Biomedical Preprints)"
source_url: "https://www.biorxiv.org/content/10.64898/2026.09.22.753526v1?rss=1"
published_at: "2026-09-28T12:00:00.000Z"
evidence_level: "Verified Feed"
license: "CC-BY-NC-4.0 / Informational Use"
---
# Whole-Brain Activation Patterns After Mu Opioid and NOP Receptor Agonism Reveal Regional and Netwo
## Provenance & Clinical Metadata
- **Canonical URL:** https://medichelpline.com/clinical-feed/biorxiv-4-whole-brain-cellular-activation-after-mu-and-nop-receptor-agonism-identifies
- **Specialty:** [Pharmacology](https://medichelpline.com/clinical-feed/pharmacology.md)
- **Primary Source:** bioRxiv (Biomedical Preprints)
- **Source URL:** [Original Journal Publication](https://www.biorxiv.org/content/10.64898/2026.09.22.753526v1?rss=1)
- **Published At:** 2026-09-28T12:00:00.000Z
- **Evidence Rating:** Verified Feed
## Executive GIST (TL;DR)
- The study used TRAP2/Ai9 reporter mice to permanently label neurons active via the c-Fos locus with tdTomato, then applied tissue clearing and light-sheet microscopy to map whole-brain activation after pharmacologic manipulation. - Treatments were acute morphine (10 mg/kg), an escalating twice-daily morphine regimen that produced dependence, and the NOP receptor agonist Ro 64-6198. - All drug treatments increased global neuronal activation relative to vehicle despite Gi/o-coupled inhibitory signaling of the receptors; the whole-brain increase reached statistical significance only in males. - Acute morphine engaged the largest number of brain regions: every measured region showed increased activation with none decreased following acute morphine. - Sex differences were prominent: males showed greater sensitivity across treatments. In males, morphine activated mainly **pain- and reward-related midbrain circuitry**; in females, morphine engagement centered on **hypothalamic circuitry**. - In mice rendered dependent by the escalating morphine regimen, activation was reduced across several regions compared with acute morphine; a cluster of cerebellar regions trended toward reduced activation or being turned off. - NOP receptor activation (Ro 64-6198) produced a substantially weaker activation profile than mu agonism. - Although chronic morphine produced less absolute activation than acute morphine, it resulted in more widespread co-activation across regions; global network organization was preserved across conditions but hub composition differed. - The TRAP2/Ai9 model provides genetic access to activated regions for future site-directed functional studies. - Data and analysis code for the study are available via the authors’ repository links reported in the source.
## Clinical Analysis & Structured Key Points
Whole Brain Cellular Activation After Mu and NOP Receptor Agonism Identifies Differential Regional and Network Consequences | bioRxiv Skip to main content New Results Whole Brain Cellular Activation After Mu and NOP Receptor Agonism Identifies Differential Regional and Network Consequences View ORCID Profile Madeline Martinez , View ORCID Profile Akihiko Ozawa , View ORCID Profile Daniel Van Zant , View ORCID Profile Jake Thornberry , View ORCID Profile Lawrence Toll doi: https://doi.org/10.64898/2026.09.22.753526 Madeline Martinez Florida Atlantic University Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Madeline Martinez Akihiko Ozawa Florida Atlantic University Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Akihiko Ozawa Daniel Van Zant Florida Atlantic University Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Daniel Van Zant Jake Thornberry Florida Atlantic University Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Jake Thornberry Lawrence Toll Florida Atlantic University Find this author on Google Scholar Find this author on PubMed Search for this author on this site ORCID record for Lawrence Toll For correspondence: ltoll{at}health.fau.edu Abstract Info/History Metrics Supplementary material Data/Code Preview PDF Abstract Mu opioid agonists, the most widely used opioids, produce analgesia, respiratory depression, constipation, and reward leading to substance abuse. Like all opioid receptor family members, mu receptors are Gi/o-coupled and inhibitory, yet mu-mediated disinhibition of GABAergic neurons propagates downstream activation that differs between naive and dependent animals and across receptor subtypes. Here we used TRAP2/Ai9 reporter mice, which deposit tdTomato in active neurons via the c-Fos locus, with tissue clearing and light sheet microscopy to map whole-brain neuronal activation after acute morphine (10 mg/kg), an escalating twice-daily morphine regimen producing dependence, or the NOP receptor agonist Ro 64-6198. Despite Gi/o coupling, all treatments raised global activation relative to vehicle, though this whole-brain increase reached significance only in males, and acute morphine engaged the largest number of regions, all increased with none decreased. Sex differences were prominent: males were more sensitive than females across treatments, with morphine engaging mainly pain- and reward-related midbrain circuitry in males and hypothalamic circuitry in females. In dependent mice, activation was lower across several regions, including a cluster of cerebellar regions that trended toward being turned off relative to acute morphine. NOP receptor activation produced a far weaker profile. Although chronic morphine produced less activation than acute morphine, it produced more widespread co-activation, and while hub composition differed across conditions, global network organization was preserved. These results reveal whole-brain changes in neuronal activation and establish a TRAP2/Ai9 model that renders activated regions genetically accessible for future site-directed investigation. Competing Interest Statement The authors have declared no competing interest. Footnotes https://github.com/toll-lab-code/cfos-opioid-brain-analyses https://doi.org/10.5281/zenodo.22754844 https://doi.org/10.5281/zenodo.22755396 Funder Information Declared National Institute on Drug Abuse , DA023281 National Institute of Neurological Disorders and Stroke , R34NS121875 U.S. Department of Defense , W81XWH2110410 Copyright The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY 4.0 International license . Back to top Previous Next Posted September 28, 2026. Download PDF Supplementary Material Data/Code Email Thank you for your interest in spreading the word about bioRxiv. NOTE: Your email address is requested solely to identify you as the sender of this article. Your Email * Your Name * Send To * Enter multiple addresses on separate lines or separate them with commas. 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Share Whole Brain Cellular Activation After Mu and NOP Receptor Agonism Identifies Differential Regional and Network Consequences Madeline Martinez , Akihiko Ozawa , Daniel Van Zant , Jake Thornberry , Lawrence Toll bioRxiv 2026.09.22.753526; doi: https://doi.org/10.64898/2026.09.22.753526 Share This Article: Copy Citation Tools Whole Brain Cellular Activation After Mu and NOP Receptor Agonism Identifies Differential Regional and Network Consequences Madeline Martinez , Akihiko Ozawa , Daniel Van Zant , Jake Thornberry , Lawrence Toll bioRxiv 2026.09.22.753526; doi: https://doi.org/10.64898/2026.09.22.753526 Citation Manager Formats BibTeX Bookends EasyBib EndNote (tagged) EndNote 8 (xml) Medlars Mendeley Papers RefWorks Tagged Ref Manager RIS Zotero Tweet Widget Facebook Like Google Plus One Subject Areas All Articles Animal Behavior and Cognition (8052) Biochemistry (18838) Bioengineering (14978) Bioinformatics (44644) Biophysics (22689) Cancer Biology (19819) Cell Biology (27009) Clinical Trials (138) Developmental Biology (14025) Ecology (21111) Epidemiology (2067) Evolutionary Biology (25523) Genetics (16215) Genomics (23581) Immunology (18778) Microbiology (42674) Molecular Biology (18151) Neuroscience (93858) Paleontology (703) Pathology (2996) Pharmacology and Toxicology (5113) Physiology (8156) Plant Biology (16061) Scientific Communication and Education (2100) Synthetic Biology (4584) Systems Biology (10272) Zoology (2395)
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