PROJECT SUMMARY
The ability to seek reward and avoid potential threats is fundamental to the fitness and survival of all animals
from early life stages. Our research aims to address circuit-wide mechanisms with cellular and molecular clarity
employing larval zebrafish. As a vertebrate genetic model organism, zebrafish shares considerable similarity
with mammals. In both mammals and larval zebrafish (See Preliminary data section), the lipid neurotransmitters
endocannabinoids (eCB) and the neuropeptide hypothalamic corticotropin releasing factor (Hy CRF) are known
to regulate motivated behaviors. However, an understanding of their roles circuit-wide at cellular resolution
is currently lacking. Larval zebrafish with a relatively simple and transparent brain of ~100K neurons (compared
to ~75 million in the mouse, and ~100 billion in the human brain) is well suited to address this question. New
regulatory principles uncovered in simpler systems will lay foundation for studying more complex systems.
Free-living with the need to hunt for food and avoid predators, larval zebrafish display readily observable
approach and avoidance behaviors in response to environmental stimuli, drugs, or social cues. Here I propose
to elucidate the role of eCB and Hy CRF, brain-wide at cellular resolution, in the context of light/dark preference,
a fundamental motivated behavior conserved across species. Larval zebrafish avoid dark, which can be
enhanced by stressors and alleviated by anxiolytics. Our preliminary data show that ablation of Hy CRF neurons
ameliorates, whereas inhibition of the cannabinoid receptor CB1 enhances, dark avoidance. We have genetically
disrupted major genes in the eCB signaling pathway, including CB1 (primarily neural) and CB2 (primarily
immune) receptors, receptor-interacting proteins (CNRIP1a and CNRIP1b), eCB synthesis enzymes (e.g.
DAGLa, DAGLb, ABHD4), and eCB degradation enzymes (MGLL, FAAH). These knockout animals are valuable
resources for understanding signaling specificity by uncovering which receptors and ligands and associated
regulatory proteins are involved in specific behavioral regulation. Furthermore, we have established brain-wide
calcium imaging and computational platforms for examining the activity and plasticity of distributed neural circuits
at cellular resolution.
In this application, built on these preliminary data and our expertise in studying brain development and function
employing zebrafish, we will test the hypothesis that eCB signaling regulates dark avoidance circuitry that
involves Hy CRF neurons. We will gain circuit-wide understanding and uncover new cell types/molecules for
future studies of circuit assembly and plasticity under stress or drug treatment in a highly accessible brain.
Impact and Outcomes: If successful, this project will achieve, for the first time to our knowledge, a cellular
resolution circuit-wide understanding of eCB signaling in relation to Hy CRF in a fundamental motivated behavior.
Such improved understanding at the whole circuitry level shall lay foundation for informing future marijuana policy
and for tackling disease states associated with perturbed CRF or eCB signaling.