As we have seen from the morphological appearances described above, two basic types of photoreceptor, rods and cones, exist in the vertebrate retina (Fig. 13). The rods are photoreceptors that contain the visual pigment – rhodopsin and are sensitive to blue-green light with a peak sensitivity around 500 nanometers (nm) wavelength of light (Fig. 14a). Rods are highly sensitive photoreceptors and are used for vision under dark-dim conditions at night. Cones contain cone opsins as their visual pigments and, depending on the exact structure of the opsin molecule, are maximally sensitive to either long wavelengths of light (red light), medium wavelengths of light (green light) or short wavelengths of light (blue light). Cones of different wavelength sensitivity and the consequent pathways of connectivity to the brain are, of course, the basis of color perception in our visual image.
Toll-like receptor 3, melanoma differentiation-associated protein 5-, and IFN-promoter stimulator 1-deficient mice were treated with poly-ICLC 24 hours before middle cerebral artery occlusion. Infarct volume was measured 24 hours after stroke to identify the receptor signaling pathways involved in protection. IFN-α/β induction was measured in plasma samples collected 6 hours after poly-ICLC treatment. IFN-β-deficient mice were used to test the requirement of IFN-β for poly-ICLC-induced neuroprotection. Mice were treated with recombinant IFN-α-A to test the role of IFN-α as a potential mediator of neuroprotection.