The Czar of Contrast

"What cellular and molecular mechanisms enable us to visually perceive the world around us? During my doctoral research, I have set out to explore the molecular signaling properties in the outer portion of the vertebrate retina to determine how these cells communicate with each other in order to craft our visual experience. I am interested in how retinal interneurons (i.e. horizontal cells, as pictured here) use lateral inhibition to modulate the visual signal from photoreceptors to second order neurons. A light stimulus starts a signaling cascade in the photoreceptors and ultimately leads to visual information getting sent to the brain for higher processing via the optic nerve. During this time, the signal initiated by the light stimulus undergoes a myriad of modifications by interneurons in order to “finely tune” the visual signal through a series of both excitatory and inhibitory synaptic connections. This complex meshwork of nerve cells in the retina modulate signal transduction in order to create the center-surround receptive fields that are so essential to creating contrast in our visual world. The attached image is of a horizontal interneuron taken from the retina of a catfish. The cell is dyed with the pH-sensitive fluorescent dye HAF to indicate the relative H+ ion concentration in the area immediately next to the cell. The image was taken on an Olympus Fluorescent microscope and pseudo-colored using ImageJ."