Cannabinoid Receptor Type 1 regulates growth cone filopodia and axon dispersion in the optic tract of Xenopus laevis tadpoles.

Previous studies show that the main cannabinoid receptor in the brain-cannabinoid type 1 receptor (CB1R)-is required for establishment of axonal projections in developing neurons but questions remain regarding the cellular and molecular mechanisms, especially in neurons developing in their native environment. We assessed the effects of CB1R signalling on growth cone filopodia and axonal projections of retinal ganglion cells (RGCs) in whole mount brains from Xenopus laevis tadpoles. Our results indicate that growth cones of RGC axons in brains from tadpoles exposed to a CB1R agonist had fewer filopodial protrusions, whereas growth cones from tadpoles exposed to a CB1R inverse agonist had more filopodia than growth cones of RGC axons in whole brains from control tadpoles.

Microinjection of DNA into Eyebuds in Xenopus laevis Embryos and Imaging of GFP Expressing Optic Axonal Arbors in Intact, Living Xenopus Tadpoles.

The primary visual projection of tadpoles of the aquatic frog Xenopus laevis serves as an excellent model system for studying mechanisms that regulate the development of neuronal connectivity. During establishment of the retino-tectal projection, optic axons extend from the eye and navigate through distinct regions of the brain to reach their target tissue, the optic tectum. Once optic axons enter the tectum, they elaborate terminal arbors that function to increase the number of synaptic connections they can make with target interneurons in the tectum.