# Anesthesia and Sleep: Mechanisms of Generating Two Similar Yet Distinct Unconscious States in the Medulla

> **NIH NIH R35** · UNIVERSITY OF PENNSYLVANIA · 2024 · $406,250

## Abstract

Although the exact mechanisms by which anesthetics induce unconsciousness remain unknown, there is
evidence that some anesthetics activate neural circuits regulating sleep and inhibit neural systems promoting
waking. Despite general anesthesia and sleep both activating a subset of seemingly similar, if not identical,
neurons, there are clear differences between the two unconscious states, including the degree of arousal
threshold changes and the timescale of state transition. The neural mechanisms underlying these related, yet
distinct unconscious states are poorly understood.
The parafacial zone (PZ) has recently been identified as a non-rapid-eye-movement (non-REM) sleep-promoting
region; specifically, GABAergic neurons in the PZ (PZ-GABA) are active during non-REM sleep. My preliminary
data demonstrate that PZ-GABA are also active during isoflurane exposure, and ablation of PZ-GABA increases
resistance to isoflurane. The results also suggest that non-GABAergic neurons within the PZ are also involved
in isoflurane-induced hypnosis. The overarching question asks how the neural circuitry driving distinct states
of non-REM sleep and isoflurane anesthesia converge and diverge by first examining in PZ-GABA neurons, and
then expanding beyond the PZ to consider all cell types in the medulla. It is hypothesized that these distinct
endogenous and drug-induced unconscious states are generated by partially overlapping shared circuits but that
key state differences arise from distinctive cellular activation patterns.
The three key questions we will address during this proposal are: 1) Does acute reversible activation/inhibition
of the PZ sleep-promoting neurons alter anesthetic sensitivity? 2) What is the cellular makeup of the PZ, and
which cells are activated during each unconscious state? and 3) What are the overlapping and different elements
between the brainstem neural circuits engaged during isoflurane exposure and those engaged during non-REM
sleep? These questions will be addressed by anesthetic and sleep phenotyping assays, the single-cell level
transcriptomic analysis by single nucleus RNA sequencing followed by multiplex in situ hybridization, and side-
by-side comparison of ensembles of active neurons by Targeted Recombination in Active Population (TRAP).
The proposed projects will uncover the underlying mechanism of how the brainstem neural circuits, including
PZ, mediate these two different unconscious states. Understanding how the brain controls states of
unconsciousness is vital for clinical practice. It can lead to more effective and safer somnogens and new potential
sedative hypnotic anesthetics that may one day be used for sleep disorders such as insomnia and narcolepsy.

## Key facts

- **NIH application ID:** 10899466
- **Project number:** 5R35GM151166-02
- **Recipient organization:** UNIVERSITY OF PENNSYLVANIA
- **Principal Investigator:** Toshihiro Imamura
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $406,250
- **Award type:** 5
- **Project period:** 2023-09-01 → 2028-08-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10899466

## Citation

> US National Institutes of Health, RePORTER application 10899466, Anesthesia and Sleep: Mechanisms of Generating Two Similar Yet Distinct Unconscious States in the Medulla (5R35GM151166-02). Retrieved via AI Analytics 2026-05-24 from https://api.ai-analytics.org/grant/nih/10899466. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*