We used acrylamide-azobenzene-quaternary ammonium (AAQ), a K+ channel photoswitch that enables optical control of neuronal excitability (Banghart et al., 2009 and Fortin et al., 2008). AAQ was originally thought to conjugate to K+ channels (Fortin et al., 2008), but recent work shows that the molecule interacts noncovalently with the cytoplasmic side of the channels, similar to the mechanism of action of local anesthetics (Banghart et al., 2009). The trans form of AAQ blocks K+ channels and increases excitability, whereas photoisomerization to the cis form with short wavelength

light (e.g., 380 nm) unblocks K+ channels and decreases excitability. PD0332991 nmr Relaxation from cis to trans occurs slowly in darkness but much more rapidly in longer-wavelength light (e.g., 500 nm), enabling rapid bi-directional photocontrol of neuronal firing with different wavelengths. We show that AAQ confers robust

light responses in RGCs in retinas from mutant mice that lack rods and cones. Moreover, after a single intraocular injection, AAQ restores light-driven behavior in blind mice in vivo. Because it is a rapid and reversible drug-like small molecule, AAQ represents a class of compounds that has potential for the restoration of visual function in humans with end-stage photoreceptor degenerative disease. We tested whether AAQ can impart light sensitivity on retinas from 6-month-old rd1 see more mice, a murine model of RP. The homozygous rd1 mouse (rd1/rd1) has a mutation in the gene encoding the β-subunit of cGMP phosphodiesterase-6, essential for

rod phototransduction. Rods and cones in these mice degenerate nearly completely within 3 months after birth, leading to a loss of electrical and behavioral light responses ( Sancho-Pelluz et al., 2008). We placed the rd1 mouse retina onto a multi-electrode array (MEA) that enables simultaneous extracellular recording found from many RGCs ( Meister et al., 1994). Before AAQ application, light generated no measurable change in RGC firing. However, after 30 min of treatment with AAQ, nearly all RGCs responded to light ( Figure 1A). Photosensitization increased with AAQ concentration ( Figure S1; Table S1 available online), but we used 300 μM for our standard ex vivo treatment. Light responses slowly diminished but were still robust for >5 hr after removing AAQ from the bathing medium ( Figure S2a). Light responses could also be detected in three of four recordings from retinas removed from rd1 mice that had received in vivo intravitreal AAQ injections 12 hr previously ( Figure S2b). The degree of photosensitivity varied, reflecting inaccurate injection in the small intravitreal volume of the mouse eye (2–3 μl). Most RGCs exhibited an increase in firing rate in response to 380 nm light and a decrease in 500 nm light, opposite to AAQ-mediated light responses in neurons in culture (Fortin et al., 2008).