# Role of Anterior Cingulate Cortex Ensemble Regulation of Spinal Cord Excitability in Associative Opioid Analgesic Tolerance.

> **NIH NIH K99** · YALE UNIVERSITY · 2024 · $181,040

## Abstract

Project Summary
Opioid medications are highly prescribed for pain management. However, these drugs have considerable abuse
liability. As users increase their opioid intake, they build tolerance against their therapeutic effects. Despite well-
described molecular and cellular mechanisms, tolerance can be reversed when the drug is taken in another
context, a phenomenon known as associative analgesic tolerance. Since associative analgesic tolerance can
lead to escalation of use, it increases the risk of opioid use disorder and fatal overdose. Uncovering neuronal
mechanisms underlying associative analgesic tolerance will inform the development of new treatment options to
mitigate pain while decreasing opioid use and overdoses. Using a novel behavioral training paradigm in mice, I
identified brain regions activated by tolerance. The anterior cingulate cortex (ACC) plays a crucial role in
contextual learning, nociception, and opioid analgesia, which are aspects of associative tolerance. My
preliminary data indicate that associative tolerance induces the formation of a tolerance-active neuronal
ensemble in the ACC (ACCtol-active). Preliminary studies using fiber photometry and chemogenetic approaches
suggest that ACC activity tracks tolerance state and is necessary for associative tolerance expression. These
data indicate that the ACC may be an orchestrator of associative tolerance. The ACC projects directly to the
spinal cord (SC), and activation of this projection increases nociception. I hypothesize that ACCtol-active neurons
produce associative tolerance by integrating context and drug signals to increase SC excitability in the presence
of opioids. In the K99 phase, I will determine the role of the ACCtol-active ensemble in associative tolerance using
a combination of transgenic tools for ensemble tagging, fiber photometry, and optogenetics. I anticipate that
ACCtol-active activity will be upregulated during tolerance and that the bi-directional modulation of this ensemble
will induce or prevent tolerance. In the R00 phase, I will use viral-mediated tracing and chemogenetic approaches
to determine if ACCtol-active forms functional connections onto the SC and if modulating this pathway can alter
associative tolerance. These experiments will help define the role of specific ACC ensembles and the ACC to
SC circuit in associative analgesic tolerance. In addition to significant scientific advances in understanding the
neural substrates driving contextual control of analgesic tolerance, this K99 proposal will provide me with training
and mentorship to increase my technical and academic skills, building a foundation for my career as an
independent investigator with my research laboratory. During the training phase, I will acquire extensive training
in optical techniques, corticospinal circuit manipulations in vivo, and career development. This training, combined
with my expertise in behavioral pharmacology and addiction models, will equip me to transition ...

## Key facts

- **NIH application ID:** 10949209
- **Project number:** 1K99DA060951-01
- **Recipient organization:** YALE UNIVERSITY
- **Principal Investigator:** Rafael E Perez
- **Activity code:** K99 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $181,040
- **Award type:** 1
- **Project period:** 2024-06-15 → 2026-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10949209

## Citation

> US National Institutes of Health, RePORTER application 10949209, Role of Anterior Cingulate Cortex Ensemble Regulation of Spinal Cord Excitability in Associative Opioid Analgesic Tolerance. (1K99DA060951-01). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/10949209. Licensed CC0.

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