The funding establishes the Polysubstance Addiction Research Center, or PARC, a multidisciplinary center led by Olivier George, PhD, professor of psychiatry at UC San Diego School of Medicine. The center assembles investigators from psychiatry, medicine, obstetrics and gynecology and reproductive sciences, and computational biology and bioinformatics, in partnership with the Veterans Affairs San Diego Healthcare System. Its stated mission is to uncover the biological factors that contribute to addiction across multiple substances, rather than studying one drug class at a time.

George, who directs PARC, argues that the traditional division of the field does not reflect how addiction actually occurs. People frequently use more than one substance, he notes, so researchers need to understand what these substances have in common as well as what makes them different. By bringing psychostimulant research — a category that includes cocaine, which speeds up activity in the central nervous system — together with opioid and alcohol research under one organizational roof, the center hopes to identify biological mechanisms that may be shared across substances and others that are specific to particular drug classes.

The scientific scope of the center is deliberately broad. PARC will focus its experimental work on cocaine, oxycodone, alcohol, and the combination of cocaine and oxycodone, using a coordinated research strategy in which the same questions are asked across all four exposure conditions. Rather than examining a single biological system in isolation, the investigators will study behavior alongside changes in brain networks, gene activity, and processes involving the immune system, metabolism, and the gut-brain connection. The goal is to understand why some individuals develop more severe addiction-related behaviors than others, and to do so by looking at multiple biological systems simultaneously.

Central to this effort is what the center calls its One-Individual Multiscale Atlas, a framework for integrating information that ranges from genes and individual cells to brain circuits, peripheral organs, and behavior. In practical terms, the atlas is meant to connect measurements made at one biological level with measurements made at another: how a change in gene expression within a specific type of brain cell relates to altered communication across a neural network, and how both relate to observable behavior. Findings generated in the laboratory will then be compared with human genetic, brain imaging, and other biological datasets to determine whether the patterns observed in preclinical models align with variation seen in people.

Abraham Palmer, PhD, professor and vice chair of basic research in the Department of Psychiatry at UC San Diego School of Medicine, emphasizes the genetic dimension of this approach. Decades of research have established that genetic differences among individuals contribute to risk for addiction, and Palmer describes PARC as using cutting-edge techniques to understand how those individual differences shape addiction risk at the molecular, cellular, and brain circuit levels. The multiscale design is intended to bridge the gap between statistical genetic associations and the biological mechanisms those associations may point toward.

The center’s work is organized into three interconnected research projects. The first, a brain connectomics project, will examine how addiction changes the organization and communication of brain networks — asking, in effect, whether repeated exposure to cocaine, oxycodone, alcohol, or their combination produces measurable shifts in how regions of the brain talk to one another. The second, a brain transcriptomics project, will study changes in gene activity within specific types of brain cells, a level of resolution that has become possible with modern single-cell and cell-type-specific molecular methods. The third, a gut-vagus multiomics project, will investigate how the gut and the vagus nerve — the cranial nerve that connects the brain with organs throughout the body — may influence addiction-related behaviors, reflecting growing scientific interest in the role of peripheral physiology and the microbiome-gut-brain axis in neuropsychiatric conditions.

Together, these projects support the center’s first formal aim: identifying biological markers associated with vulnerability to addiction-related behaviors. Advanced computational and machine-learning methods will be used to integrate the different types of data the projects generate and to identify patterns that may help explain differences in addiction severity. The second aim goes a step further, moving from correlation to causation. Researchers will use medications and other interventions to test whether potential biological targets identified through the center’s research — including pathways involved in cellular stress, immune signaling, and communication between the gut and the brain — actually influence addiction-related behavior when manipulated. As George puts it, the goal is to go beyond simply finding a biological difference associated with addiction and to test whether changing that biological process changes the behavior itself, an approach he argues is more likely to yield targets that translate into new treatments.

The third aim is infrastructural. PARC will expand an addiction biobank that already contains more than 40,000 specimens collected from studies of addiction-related behaviors involving cocaine, oxycodone, and alcohol, a resource that has supported 75 external research projects to date. The center will also provide researchers with access to standardized behavioral models, computational tools, and shared datasets, with data deposited in National Institutes of Health repositories to support reproducibility and allow other laboratories to build on the center’s findings. In this respect, PARC is designed not only as a research program but as a national resource for addiction science.

The new center formalizes and expands a collaboration that has been building at UC San Diego for six years. During that period, PARC investigators have worked across more than a dozen laboratories, producing hundreds of publications and developing shared research resources. Barbara Jung, MD, associate vice chancellor and dean of UC San Diego School of Medicine, describes the award as a recognition of George’s leadership and his vision for bringing researchers across disciplines to address the complexities of addiction, and says the creation of PARC strengthens the school’s ability to lead collaborative research that can deepen understanding of addiction and help identify new approaches to prevention and treatment. By connecting biological information across multiple levels and bridging the historical divide between alcohol and drug research, PARC aims to move the field from isolated observations toward an integrated account of why addiction develops, why some people are more vulnerable than others, and why relapse occurs.

Subject of Research: A NIDA-funded multidisciplinary center studying the shared biology of polysubstance addiction across cocaine, oxycodone, and alcohol

Article Title: UC San Diego receives $12.6 million award to launch a new polysubstance addiction research center

Article References: UC San Diego receives $12.6 million award to launch a new polysubstance addiction research center. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: polysubstance addiction, NIDA, UC San Diego, Olivier George, brain connectomics, transcriptomics, gut-brain axis, vagus nerve, cocaine, oxycodone, alcohol use disorder, biobank

The significance of self-administration models in addiction neuroscience is difficult to overstate. Unlike passive drug exposure experiments, in which the investigator simply injects an animal with a drug and observes the consequences, self-administration paradigms allow the animal itself to control when and how much drug it receives, typically by pressing a lever or poking its nose into a port. This voluntary element matters enormously. It allows investigators to dissociate the behavioral and neural mechanisms that motivate drug seeking and taking from the pharmacological effects of drug exposure itself, a distinction that lies at the heart of modern addiction research. Compulsive drug taking, relapse after abstinence, and the escalation of intake over time are all phenomena that only emerge when the animal has agency over its own drug consumption.

The intellectual lineage of this approach stretches back more than eight decades. As the authors note in their News and Views commentary accompanying the protocol, the earliest demonstrations that animals will work to obtain drugs appeared in the comparative psychology literature of 1940, when Spragg reported that chimpanzees would manipulate mechanisms to gain access to morphine. In the mid-1950s, Headlee, Coppock, and Hichols described intravenous morphine administration procedures in the Journal of Pharmaceutical Sciences, laying groundwork for controlled delivery of drugs into the bloodstream of laboratory animals. These early efforts culminated in a landmark 1962 study by James Weeks, published in Science, which established the operant intravenous drug self-administration procedure in rats—a technique that remains the workhorse of preclinical addiction research to this day.

The field built rapidly on that foundation. Thompson and Schuster demonstrated in 1964 that the principles of operant conditioning could be applied to morphine self-administration, and Risner and Jones extended the approach in 1975 to compare the reinforcing effects of different drugs. By 1991, Carney and colleagues were using self-administration procedures to study stimulant pharmacology, and the paradigm had become a standard screen for the abuse liability of novel compounds. A 2020 review by Venniro, Banks, Heilig, Epstein, and Shaham in Nature Reviews Neuroscience synthesized how decades of self-administration research had refined the field’s understanding of the neural circuits of drug reward, relapse, and the economic and social factors that influence drug taking. The historical arc is clear: each generation of methodological refinement has allowed sharper questions to be asked about why drugs are so compelling.

What the new protocol adds is the head-fixed dimension. In a conventional self-administration chamber, a mouse moves freely, presses levers, and receives intravenous infusions through a catheter implanted in its jugular vein. This arrangement is behaviorally rich but experimentally constrained. The animal’s head moves unpredictably, which degrades optical recordings, complicates the delivery of precisely timed sensory stimuli, and makes it nearly impossible to hold a microscope objective or a stimulus display in a fixed relationship to the animal’s eyes and whiskers. Head fixation solves these problems. With the skull rigidly stabilized, researchers can perform stable two-photon imaging of the same population of neurons across many sessions, deliver visual or auditory cues with millisecond precision, and apply optogenetic or pharmacological manipulations to genetically identified circuits while the animal is actively working for drug.

Combining head fixation with intravenous self-administration, however, is far from trivial, and this is precisely where the protocol makes its contribution. The authors provide step-by-step instructions for assembling the necessary hardware, integrating the head-fixation apparatus with the operant response devices and the infusion system that delivers drug through the implanted catheter. The technical challenges are considerable: the catheter must remain patent across repeated sessions while the animal is restrained; the operant manipulandum must be positioned so that a head-fixed mouse can respond comfortably; and the infusion line must be routed so that drug delivery is synchronized with the animal’s responses without introducing movement artifacts or leaks. By documenting these details, the protocol lowers the barrier for laboratories that want to adopt the technique without months of trial and error.

The timing of this methodological advance reflects a broader convergence in the field. A companion protocol by Doncheck and colleagues, also published in Nature Protocols in 2026 and cited in the commentary, indicates that head-fixed drug self-administration is emerging as a coherent methodological platform rather than the idiosyncratic setup of a single laboratory. Meanwhile, recent work published in Neuron in 2024 by Paniccia and colleagues demonstrated the scientific payoff of head-fixed approaches, and a 2021 study by Vollmer and colleagues in Frontiers in Behavioral Neuroscience explored related territory in freely moving animals. Together, these publications sketch a research landscape in which the voluntary taking of intravenous drugs can finally be observed with the full arsenal of modern circuit neuroscience.

For researchers weighing whether to adopt the technique, the trade-offs are worth understanding. Freely moving self-administration preserves the naturalistic ethology of drug seeking—the animal navigates its environment, approaches the drug source, and integrates spatial and contextual cues into its behavior. Head-fixed preparations sacrifice some of that naturalism in exchange for experimental control and optical stability. The authors’ framing suggests that the two approaches should be viewed as complementary rather than competing: freely moving studies establish the validity of a behavioral phenomenon, while head-fixed preparations dissect its circuit-level mechanisms with cellular precision. A protocol that makes the head-fixed variant accessible and reproducible therefore expands the toolkit available to the field rather than replacing the established one.

The potential applications span the major questions of addiction neuroscience. With a head-fixed mouse pressing a port for intravenous cocaine, opioid, or other drug infusions, investigators could track how neurons in the prefrontal cortex, nucleus accumbens, dorsal striatum, or amygdala change their activity as drug seeking becomes habitual, as intake escalates, or as cues that predict drug availability come to drive behavior. They could test whether manipulating specific projections alters the propensity to seek drug, and they could do so across many consecutive sessions with imaging planes held perfectly stable. Because the animals are mice rather than rats, the full power of mouse genetics—cell-type-specific reporters, conditional knockouts, and activity-dependent labeling—becomes available to self-administration research in ways that were previously cumbersome.

As with any methodological innovation, the ultimate test will be how widely the technique is adopted and what it reveals. The authors declare no competing interests, and the protocol, published as a U.S. Government work, is accompanied by supplementary information including an additional figure and references to support implementation. For a field that has spent more than sixty years refining the operant self-administration paradigm since Weeks first described it in Science, the arrival of a validated head-fixed variant marks a genuine expansion of the frontier. If it delivers on its promise, the coming years should see drug self-administration experiments in which every lever press is paired with a window into the living brain—bringing addiction neuroscience closer to the mechanistic depth that the problem of addiction demands.

Subject of Research: A protocol for performing intravenous drug self-administration in head-fixed mice to study the neural mechanisms of addiction.

Article Title: Head-fixed intravenous drug self-administration: a new frontier in addiction neuroscience

Article References: Negishi, K., D’Ottavio, G., & Shaham, Y. (2026). Head-fixed intravenous drug self-administration: a new frontier in addiction neuroscience. Nature Protocols. https://doi.org/10.1038/s41596-026-01438-7

Image Credits: AI Generated

DOI: 10.1038/s41596-026-01438-7

Keywords: addiction neuroscience, drug self-administration, head-fixed mice, intravenous drug delivery, Nature Protocols, behavioral neuroscience, two-photon imaging, operant conditioning, drug reward, relapse, NIDA, mouse models