# Functional Heterogeneity of Hypocretin Neurons

> **NIH NIH R01** · STANFORD UNIVERSITY · 2021 · $462,855

## Abstract

Functional heterogeneity of Hcrt neurons
Complex neuronal circuits regulate arousal, and deficiencies in these circuits are a highly prevalent
cause for sleep disturbances and anxiety disorders. The multi-functional hypocretin/orexin (Hcrt)
neurons regulate arousal-related behavioral states including sleep, wakefulness, feeding,
emotions, stress and reward. However, how a presumably uniform Hcrt population regulates such
diverse functions, and how alteration in these circuitries result in sleep and anxiety disorders is
not clear. We hypothesize that Hcrt neurons are genetically, anatomically and functionally
heterogenous, and that subpopulations of Hcrt neurons projecting to different brain regions
regulate specific features of sleep and arousal. Here, we will use a combination of viral
monosynaptic circuit tracing, two-photon live imaging of single synapse and neuronal activity,
optogenetics, fiber photometry and behavioral experiments in zebrafish and mice to identify and
elucidate the function of subpopulations of Hcrt neurons in regulating sleep. In aim 1, we will use
retrogradely transported viral vectors and live imaging of single pre- and post-synaptic structure
to characterize anatomically distinct subpopulations of Hcrt neurons, innervating the VTA, LC and
TMN regions. The transparent zebrafish model enables anatomical and functional live
visualization of the relatively simple, but conserved, Hcrt system (20-40 cells). In aim 2, fiber
photometry recording in behaving mice and real-time two-photon imaging of neuronal activity in
single cell resolution will be performed to elucidate the differential neuronal activity of
subpopulations of Hcrt neurons in regulating sleep and arousal. In aim 3, optogenetic, synaptic
silencing and genetically induced neuron ablation will be used to manipulate subpopulations of
Hcrt neurons. We will monitor the effect on neuronal activity in post synaptic dopaminergic and
histaminergic target neurons using genetically encoded calcium indicators. These neuronal
activity recordings will be complemented with behavioral experiments in mice. The results are
expected to challenge the generalized assumption that neurons that secrete a specific
neuropeptide share similar identities and functions. The combined strength of the two vertebrate
models will uncover the role of evolutionary conserved sub neuronal circuitries and may provide
new therapeutic targets for the treatment of sleep disorders.

## Key facts

- **NIH application ID:** 10087971
- **Project number:** 5R01MH116470-03
- **Recipient organization:** STANFORD UNIVERSITY
- **Principal Investigator:** Lior Yosef Appelbaum
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $462,855
- **Award type:** 5
- **Project period:** 2019-02-08 → 2023-11-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10087971

## Citation

> US National Institutes of Health, RePORTER application 10087971, Functional Heterogeneity of Hypocretin Neurons (5R01MH116470-03). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10087971. Licensed CC0.

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