Exploring Molecular Mechanisms That Underlie Cellular Response to Laser Stimulation in Retinal Ganglion Cells

Abstract

Purpose: : Blindness in patients with retinitis pigmentosa (RP) is associated to a primary degeneration of photoreceptors and a secondary loss of cells from the inner retinal layers. Yet in these patients most of the bipolar and retinal ganglion cells (RGC) remain intact for many years, with their ability to transduce some visual information and consequently, providing with excitable cells that can be stimulated by electrical prosthetic stimulations. Such an approach is presently impeded both by the use of conventional electrodes which cannot transmit with high fidelity the wide range of visual stimulations encountered under normal condition and by the gliosis ensuing from the presence and function of the electrodes within the sensory organ . These drawbacks could be bypassed by mid-infra red laser stimulation which allows increased spatial resolution without direct cellular contact.

Methods: : We used an experimental set up to stimulate purified RGC or retina slices with a 1870-nm wavelength beam guided by an optical fibre of 105µm diameter. We evaluated the biological response by calcium imaging and electrophysiological recordings (whole cell patch clamp method).

Results: : We demonstrated that with a stimulation threshold energy of 1J/cm2>E>3J/cm2, we can generate in RGCs reproducible calcium transients and variations of membrane potential with or without further evoked action potentials without being harmful for the neurons. The application of calcium and sodium voltage dependant channels blockers confirmed the biological effects of laser stimulation without elucidating yet the biological mechanisms triggered by this method of stimulation of this type of neuron.

Conclusions: : Based on present data, mid-infrared laser stimulation represents a realistic alternative process to stimulate RGCs and restore visual stimuli in patients suffering severe RP. Work is in progress to increase the efficiency of the laser stimulus and RGCs sensitivity. We are presently working on the identification of the cellular elements and intracellular cascades involved in the cell response.

Keywords: ganglion cells • laser • signal transduction