In vivo optical recording of the light response of primate ganglion cells

Abstract

Purpose: Current methods to record the responses of single retinal neurons require removing the retina or penetrating the globe with a microelectrode to record from one cell at a time. We describe an imaging method, FACILE (functional adaptive-optics cellular imaging in the living eye), that allows optical recording of the single-cell responses to visual stimuli from large numbers of cells simultaneously in the living primate eye.

Methods: A novel adeno-associated virus variant (7m8) was intravitreally injected to express G-CaMP5, a calcium indicator, in macaque ganglion cells (GCs). Optical recording was performed with a fluorescence adaptive-optics scanning laser ophthalmoscope at roughly weekly intervals starting 2 months after injection. G-CaMP5 fluorescence became visible 3 weeks after injection and remained stable for approximately 7 months. Intensity response functions of GCs were studied with uniform, temporally modulated 590 nm light. Receptive fields were measured with static or drifting bars produced by spatial modulation of a visible laser (488 or 568 nm). The spatial displacement of GCs from the foveal cones that drive them allowed for simultaneous imaging and stimulation without cross-talk. The retinal locations of bar stimuli during imaging were determined by analysis of intrinsic signal responses of cones to the stimuli, imaged with 794 nm light.

Results: GCs were densely transduced in the fovea, allowing simultaneous imaging of the response of many individual cells. The response of individual GCs could be measured with this method over a two order of magnitude change in light intensity. The calcium response is slow, but we can reliably detect responses of single cells to 0.5 Hz modulation. The method also allows mapping of the displacement of GC receptive fields from the cones that drive them. We found displacements up to 400 μm, consistent with anatomical estimates.

Conclusions: We have demonstrated a relatively non-invasive method to study the response properties of single primate GCs, even in the fovea where microelectrode recordings are difficult. The method can reveal the responses of many individual GCs simultaneously without requiring removal of the retina, allowing repeated measurements of the same cell over many months. This enables study of the function roles of specific cells, retinal development, the progression of retinal disease and therapeutic interventions for them.

Keywords: 531 ganglion cells • 691 retina: proximal (bipolar, amacrine, and ganglion cells) • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)