Whole-brain mapping of spinal-projecting neurons in larval zebrafish.

Whole-brain optical backfilling in larval Danio rerio reveals far more spinal-projecting neurons than conventional methods, enabling a comprehensive map of spinal-cord–projecting axon sources.

• Why it matters: SPNs are widely distributed and connect over long distances, making it difficult to map their anatomical organization and link specific populations to distinct functions.
• What they did: The study used photoactivable GFP–based optical backfilling to label all neurons whose axons project to the spinal cord, then integrated cell location, morphology, and projection patterns.
• The result: The resulting whole-brain map revisits spinal-projecting nuclei across hindbrain, midbrain, and diencephalic regions and supports tentative homological assignments to known vertebrate SPN descriptions.

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