11-cis retinal restores visual function in vitamin A-deficient Manduca

Larvae of the tobacco hornworm moth Manduca sexta were reared on either a carotenoid-supplemented or a carotenoid-deficient diet. The former yields fortified adults with normal visual function, whereas visual sensitivity and rhodopsin content are reduced by 2-4 log units in the compound eyes of the deprived moths reared on the latter. We characterized the retinoids of fortified retinas and investigated the recovery of visual function in deprived moths that were provided with retinaldehyde as a source of photopigment chromophore. Retinoids were identified and measured by high-performance liquid chromatography (HPLC). Fortified retinas contained mainly 3-hydroxyretinaldehyde (R3); 11-cis R3 predominated in dark-adaptation, all-trans in light-adaptation, indicating that R3 is the photopigment chromophore. No retinoids could be measured in deprived eyes. Retinaldehyde (R1) was delivered to the retinas of deprived moths by "painting" solutions of 11-cis or all-trans R1 in dimethylsulfoxide (DMSO) on the corneal surfaces of the compound eyes or on the head capsule between the eyes. 11-cis R1 induced rapid recovery: during 3 days, sensitivity rose to within a log unit of that measured from fortified animals. By 7 days, sensitivity was close to normal. Although rhodopsin and P-face particle densities of photoreceptor membranes increased, neither rose to the levels found in fortified animals. All-trans R1 induced only a slight increase in sensitivity that could have resulted from some nonspecific isomerization of the all-trans to the 11-cis isomer; we found no evidence for a retinal isomerase that functions in darkness. Small amounts of R3 were measured in recovering retinas, indicating some conversion of R1 to R3.(ABSTRACT TRUNCATED AT 250 WORDS)