Figure 5.

The zebrafish CP is functional and possesses size-selective properties. Casper zebrafish were intravenously injected with fluorescent tracers at 2, 3, and 4 dpf to identify tracer leakage from blood into the cerebrospinal fluid. (A) The top panel shows severe leakage of the 3-kDa fluorescein dextran into the brain ventricle (inset) at 2 dpf, minor leakage at 3 dpf, and little, if any, dextran penetration at 4 dpf. The bottom panel shows permeability of the 10-kDa rhodamine dextran at 2 dpf (inset), which decreases by 4 dpf. The 40-kDa fluorescein dextran was the least permeable at each developmental timepoint. Images were taken at 1 h post-injection. (B) A ratio of fluorescence intensity in the brain ventricle relative to the heart was measured at 30 min post-injection as a readout for tracer leakage into the brain ventricle. A One-Way ANOVA shows that the 3-kDa fluorescein dextran and the 10-kDa rhodamine dextran are significantly more permeable (i.e., greater mean fluorescence intensity) than the 40-kDa fluorescein dextran at 2 and 3 dpf. By 4 dpf, there was no significant difference in fluorescence intensity. Measurements are expressed as mean ± SE for n = 7; ^****p < 0.0001. Abbreviations: Rhod, rhodamine dextran; Flour: fluorescein dextran. Scale bar is 50 μm.