Imaging light-modulated release of synaptic vesicles in the intact retina: Retinal physiology at the dawn of the post-electrode era

Here, we illustrate an optical method for directly measuring the light-regulated synaptic output of neurons in the retina. The method allows simultaneous recording from many retinal neurons in intact flat-mount preparations of the vertebrate retina. These recordings depend on the use of FM1-43, an activity-dependent fluorescent dye that selectively labels synaptic vesicles. Release of the dye, which occurs upon vesicle exocytosis, is detected with 2-photon microscopy. This utilizes an infrared laser to trigger fluorescence excitation of the dye, while minimally perturbing retinal activity by activating phototransduction in rods and cones. Using this approach, one can measure activity of single neurons in the intact retinal network and populations of neurons in different layers of the retina, providing a new way to examine the function of retinal synapses and how visual information is processed.