Altered Swimming Behaviors in Zebrafish Larvae Lacking Cannabinoid Receptor 2

Area of Science:

• Neuroscience and Behavioral Pharmacology
• Genetics and Molecular Biology
• Drug Discovery and Development

Background:

• Cannabinoid receptor 2 (CB2) is implicated in complex brain functions and behaviors.
• Understanding CB2's role in behavior is crucial for developing targeted therapeutics.
• Existing screening methods may lack scalability for whole-organism assays.

Purpose of the Study:

• To investigate the role of CB2 in zebrafish larval swimming behaviors, particularly anxiety-like responses.
• To develop and validate an upscalable, whole-organism screening approach for CB2 ligands.
• To assess the behavioral impact of CB2 loss-of-function and its modulation by specific drugs.

Main Methods:

• Generated a novel CB2 knockout (CB2-KO) zebrafish line using CRISPR-Cas9 technology.
• Quantified anxiety-like behaviors using photo-dependent swimming responses (PDR) and center occupancy (CO).
• Administered anxiolytic (VPA) and anxiogenic (PTZ) drugs, and tested CB2-specific ligands (agonists and antagonists) in wild-type and CB2-KO larvae.

Main Results:

• CB2-KO larvae displayed distinct PDR and reduced CO compared to wild-type controls.
• Mutant larvae showed altered responses to VPA and PTZ, indicating CB2's role in modulating these drug effects.
• Two of four tested CB2 ligands demonstrated detectable activity in the developed assay.

Conclusions:

• Zebrafish larvae lacking CB2 exhibit altered complex behaviors consistent with anxiety-like phenotypes.
• CB2 plays a significant role in modulating behavioral responses to anxiolytic and anxiogenic stimuli.
• The established genetic and behavioral approach offers a scalable platform for high-throughput screening of CB2-targeting drugs.