R. H. Douglas

Melanopsin and rod-cone photoreceptive systems account for all major accessory visual functions in mice

In the mammalian retina, besides the conventional rod–cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment. On ablation of the melanopsin gene, retinal ganglion cells that normally express melanopsin are no longer intrinsically photosensitive. Furthermore, pupil reflex, light-induced phase delays of the circadian clock and period lengthening of the circadian rhythm in constant light are all partially impaired. Here, we investigated whether additional photoreceptive systems participate in these responses. Using mice lacking rods and cones, we measured the action spectrum for phase-shifting the circadian rhythm of locomotor behaviour. This spectrum matches that for the pupillary light reflex in mice of the same genotype, and that for the intrinsic photosensitivity of the melanopsin-expressing retinal ganglion cells. We have also generated mice lacking melanopsin coupled with disabled rod and cone phototransduction mechanisms. These animals have an intact retina but fail to show any significant pupil reflex, to entrain to light/dark cycles, and to show any masking response to light. Thus, the rod–cone and melanopsin systems together seem to provide all of the photic input for these accessory visual functions.

Retinal repair by transplantation of photoreceptor precursors.

Photoreceptor loss causes irreversible blindness in many retinal diseases. Repair of such damage by cell transplantation is one of the most feasible types of central nervous system repair; photoreceptor degeneration initially leaves the inner retinal circuitry intact and new photoreceptors need only make single, short synaptic connections to contribute to the retinotopic map. So far, brain- and retina-derived stem cells transplanted into adult retina have shown little evidence of being able to integrate into the outer nuclear layer and differentiate into new photoreceptors. Furthermore, there has been no demonstration that transplanted cells form functional synaptic connections with other neurons in the recipient retina or restore visual function. This might be because the mature mammalian retina lacks the ability to accept and incorporate stem cells or to promote photoreceptor differentiation. We hypothesized that committed progenitor or precursor cells at later ontogenetic stages might have a higher probability of success upon transplantation. Here we show that donor cells can integrate into the adult or degenerating retina if they are taken from the developing retina at a time coincident with the peak of rod genesis. These transplanted cells integrate, differentiate into rod photoreceptors, form synaptic connections and improve visual function. Furthermore, we use genetically tagged post-mitotic rod precursors expressing the transcription factor Nrl (ref. 6) (neural retina leucine zipper) to show that successfully integrated rod photoreceptors are derived only from immature post-mitotic rod precursors and not from proliferating progenitor or stem cells. These findings define the ontogenetic stage of donor cells for successful rod photoreceptor transplantation.

Characterization of an ocular photopigment capable of driving pupillary constriction in mice

This work demonstrates that transgenic mice lacking both rod and cone photoreceptors (rd/rd cl) retain a pupillary light reflex (PLR) that does not rely on local iris photoreceptors. These data, combined with previous reports that rodless and coneless mice show circadian and pineal responses to light, suggest that multiple non-image-forming light responses use non-rod, non-cone ocular photoreceptors in mice. An action spectrum for the PLR in rd/rd cl mice demonstrates that over the range 420–625 nm, this response is driven by a single opsin/vitamin A-based photopigment with peak sensitivity around 479 nm (opsin photopigment/OP479). These data represent the first functional characterization of a non-rod, non-cone photoreceptive system in the mammalian CNS.

The Visual System of Fish

The Visual system of fish , The Visual system of fish , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

The Eyes of Deep-Sea Fish I: Lens Pigmentation, Tapeta and Visual Pigments

Deep-sea fish, defined as those living below 200 m, inhabit a most unusual photic environment, being exposed to two sources of visible radiation; very dim downwelling sunlight and bioluminescence, both of which are, in most cases, maximal at wavelengths around 450-500 nm. This paper summarises the reflective properties of the ocular tapeta often found in these animals, the pigmentation of their lenses and the absorption characteristics of their visual pigments. Deep-sea tapeta usually appear blue to the human observer, reflecting mainly shortwave radiation. However, reflection in other parts of the spectrum is not uncommon and uneven tapetal distribution across the retina is widespread. Perhaps surprisingly, given the fact that they live in a photon limited environment, the lenses of some deep-sea teleosts are bright yellow, absorbing much of the shortwave part of the spectrum. Such lenses contain a variety of biochemically distinct pigments which most likely serve to enhance the visibility of bioluminescent signals. Of the 195 different visual pigments characterised by either detergent extract or microspectrophotometry in the retinae of deep-sea fishes, ca. 87% have peak absorbances within the range 468-494 nm. Modelling shows that this is most likely an adaptation for the detection of bioluminescence. Around 13% of deep-sea fish have retinae containing more than one visual pigment. Of these, we highlight three genera of stomiid dragonfishes, which uniquely produce far red bioluminescence from suborbital photophores. Using a combination of longwave-shifted visual pigments and in one species (Malacosteus niger) a chlorophyll-related photosensitizer, these fish have evolved extreme red sensitivity enabling them to see their own bioluminescence and giving them a private spectral waveband invisible to other inhabitants of the deep-ocean.

Ultraviolet-sensitive cones in the goldfish

Goldfish have been shown behaviourally to have ultraviolet sensitivity. We have now identified by microspectrophotometry a population of small single cones in the goldfish retina that contain a visual pigment maximally sensitive around 355-360 nm.

A review of vertebrate and invertebrate ocular filters

The spectral information available to an animal’s visual system depends both on the wavelengths reaching its outer segments and the visual pigments contained within them. The former is governed not only by the chromatic stimuli present in the environment, but also by the degree to which these are modified through intraocular filters, before being absorbed by the visual pigments. Although the ocular media of the majority of animals are transparent to light above about 310 nm, their primary function being either refractive or nutritive, in some, pigments are present that filter the spectral content of the light reaching the retina. Light impinging on the visual pigments may have its spectrum further modified by both filters within the retina itself and by reflective structures behind the retina.

Light in biology and medicine

Comprises 56 peer-reviewed and edited contributions from the third meeting (although the volume is identified as number 2; to further confuse things, the CIP for the previous conference volume is erroneously carried on the verso of the title page). The multidisciplinary nature of photobiology the st

Dragon fish see using chlorophyll

Most deep-sea fish have visual pigments that are most sensitive to wavelengths around 460-490 nm, the intensity maxima of both conventional blue bioluminescence and dim residual sunlight. The predatory deep-sea dragon fish Malacosteus niger, the closely related Aristostomias sp. and Pachystomias microdon can, in addition to blue bioluminescence, also emit far-red light from suborbital photophores, which is invisible to other deep-sea animals. Whereas Aristostomias sp. enhances its long-wavelength sensitivity using visual pigments that are unusually red sensitive, we now report that M. niger attains the same result using a derivative of chlorophyll as a photosensitizer.

The effect of dopamine depletion on light-evoked and circadian retinomotor movements in the teleost retina

The retinae of lower vertebrates undergo a number of structural changes during light adaptation, including the photomechanical contraction of cone myoids and the dispersion of melanin granules within the epithelial pigment. Since the application of dopamine to dark-adapted retinae is known to produce morphological changes that are characteristic of light adaptation, dopamine is accepted as a casual mechanism for such retinomotor movements. However, we report here that in the teleost fish, Aequidens pulcher, the intraocular injection of 6-hydroxydopamine (6-OHDA), a substance known to destroy dopaminergic retinal cells, has no effect on the triggering of light-adaptive retinomotor movements of the cones and epithelial pigment and only slightly depresses the final level of light adaptation reached. Furthermore, the retina continues to show circadian retinomotor changes even after 48 h in continual darkness that are similar in both control and 6-OHDA injected fish. Biochemical assay and microscopic examination showed that 6-OHDA had destroyed dopaminergic retinal cells. We conclude, therefore, that although a dopaminergic mechanism is probably involved in the control of light-induced retinomotor movements, it cannot be the only control mechanism, nor can it be the cause of circadian retinomotor migrations. Interestingly, 6-OHDA injected eyes never reached full retinomotor dark adaptation, suggesting that dopamine has a role to play in the retinas response to darkness.