Demonstration and use of nanoliter sampling of in vivo rat vitreous and vitreoretinal interface

An understanding of the chemical microenvironments at different locations on the retina can provide unique insights into retinal neurochemistry and pathology. The anatomical shape and the small volumes available from a spatially restricted volume greatly complicate these types of measurements. The aim of this study was to demonstrate an in vivo sampling system to probe different regions of the rat retina.

A low-flow push-pull perfusion probe was developed with concentric fused-silica capillaries. It was designed to fit through a 29-gauge needle for placement in the vitreous and at the vitreoretinal interface of the rat eye. Physiological saline was perfused and withdrawn through outer and inner capillaries, respectively, at flow rates between 10 and 50 nl/min. Samples of 500 nl were collected for amino acid analysis by capillary electrophoresis. Perfusion of a potent and selective inhibitor of the excitatory amino acid transporters was performed through the probe with the tip located 1-2 mm away from the optic nerve head.

Ten amino acids were quantified from the perfusates of vitreous and the vitreoretinal interface. Sampling through time showed the use of this system to monitor retinal changes in these amino acids. The infusion of a transport protein antagonist shows a statistically significant increase in the glutamate concentration in collected samples when the probe tip is placed peripheral to but not over the optic nerve head.

We demonstrate a new method for following neurochemical changes at the retina with spatial resolution. This in vivo method is widely applicable to the site-specific study of states of normal and dysfunctional retinal neurochemistry.