Spinal cord injury in zebrafish induced by near-infrared femtosecond laser pulses

Background: The spinal cord is composed of a large number of cells that interact to allow the organism to function. To perform detail studies of cellular processes involved in spinal cord injury (SCI), one must use repeatable and specific methods to target and injure restricted areas of the spinal cord. New method: We propose a robust method to induce SCI in zebrafish by laser light. With a 2-photon microscope equipped with a femtosecond near-infrared pump laser, we explored the effects of laser beam exposure time, area, and intensity to induce precise and repeatable SCI with minimized collateral damage to neighboring cells. Results: Through behavioral studies in zebrafish larvae, we assessed the functional outcome of intensive laser light directed at the spinal cord. Our experiments revealed that a laser pulse with wavelength 800 nm, duration 2.6 ms, and light intensity 390 mW was sufficient to induce controlled cell death in a single cell or a spinal cord segment. Collateral damage was observed if cells were exposed to laser pulses exceeding 470 mW. With these settings, we could induce precise and repeatable SCI in zebrafish larvae, resulting in loss of motor and sensory function. Comparison with existing method(s): Our method offers a simple and more controlled setting to induce SCI in zebrafish. We describe how the near-infrared femtosecond laser should be adjusted for achieving optimal results with minimal collateral damage. Conclusions: We present a precise and robust method for inducing SCI in zebrafish with single-cell resolution using femtosecond near-infrared laser pulses.