Fig. 1
From: Large molecules from the cerebrospinal fluid enter the optic nerve but not the retina of mice
Uptake of cisternally-injected dextrans along the optic nerve requires high volume injection. (A) Injection protocol for dispersion of dextrans in the sub-arachnoid space. A fixed quantity of fluorescent lysine-dextrans (FITC-2000 kDa, TRITC 70 kDa and Alexa 647 10 kDa) were injected at either low (0.5 ul/min) or high (5 ul/min) injection rates for 10 min. Animals were sacrificed by perfusion fixation 30 min after the termination of injections and the optic nerve was removed for visualization by confocal microscopy. (B) Left panel Low magnification images showing fluorescence of 70 kDa TRITC-dextran in the dissected optic nerve from animals injected according to the protocols described in A. Center and right panels High resolution images of the boxed regions at left, corresponding to regions adjacent to the point where the optic nerve enters the eye, showing uptake of each of the fluorescent dextrans. (C) Left Images of the optic nerve from B, pseudocolored to show fluorescence intensity, where red indicates high intensity, blue indicates low intensity and green indicates intermediate intensity. The dotted lines were used to calculate intensity profile. Right. Relative fluorescence intensity as a function of distance from the optic chiasm for optic nerves with high and low volume injection. (D) Quantification of the ratio of sub-arachnoid fluorescence intensity between chiasmal and tip regions of the optic nerve for each tracer under high or low volume injection conditions (n = 4 low volume vs. 5 high volume. (*p < 0.05 between high and low volume injection by t-test). (E) Analysis of the ratio between perivascular tracer intensity and sub-arachnoid intensity for each tracer after high volume injection (n = 5 ***p < 0.001 by t-test))