Characteristics of the blue sensitive cone mechanism in primate retinal ganglion cells
In psychophysical data on primates, there is remarkable consensus that the blue sensitive cones differ in many ways from the red and green sensitive ones: they are probably not contributing much to visual acuity, they have a limited space and time resolution and they contribute nothing or little to brightness, but strongly to hue; they are much less numerous and very rare in the fovea1 region. Moreover, there must be an unusual interaction between the short and long wavelength sensitive cone mechanism, since the sensitivity of the blue cone system can be changed considerably by yellow adapting lights which act exclusively on the longer wavelength sensitive cones The question raised here is, how to account for such disparities in the data on blue sensitive ganglion cells. Since confusion about the short and middle wavelength sensitive cone system can easily occur, present additional electrophysiological criteria which serve to clearly distinguish the blue sensitive cone mechanism; the unique role blue sensitive cones might play in color vision and present a circuit which accounts for some special characteristics of blue sensitive ganglion cells in rhesus monkey.The
question raised here is, how to account for such disparities in the data on
blue sensitive ganglion cells. Since confusion about the short and middle
wavelength sensitive cone system can easily occur, we will present additional
electrophysiological criteria which serve to clearly distinguish the blue
sensitive cone mechanism; we will discuss the unique role blue sensitive cones
might play in color vision and present a circuit which accounts for some special
characteristics of blue sensitive ganglion cells in rhesus monkey.
Visinin: A novel calcium binding protein expressed in retinal cone cells
Visinin is a retinal cone cell-specific protein (molecular weight 24,000, pl 5.1). To investigate its function, visinin cDNA was isolated from a chick retinal λgt11 cDNA library, using anti-visinin serum. The (β-galactosidase-visinin fusion protein was used for purifying epitope-selected antibody. The purified visinin antibody reacted only with a 24 kd protein in retinal cone cells. Visinin mRNA was expressed only in the retinal photoreceptor layer. The nucleotide sequence of the cDNA revealed that visinin has three E-F hand structures and is a Ca2+ binding protein. Visinin protein expressed in E. coli exhibited Ca2+ binding activity. These results suggest that visinin is a photoreceptor-specific Ca2+ binding protein and may be involved in phototransduction in the cone cells.
Photoreceptor Transplants Increase Host Cone Survival in the Retinal Degeneration (rd) Mouse
Retinal transplants offer a potentially interesting approach to treating human retinal degenerations, but so far little quantitative data are available on possible beneficial effects. We isolated photoreceptor layers from normal-sighted mice and grafted them into the subretinal space of retinal degeneration (rd) mice lacking rod photoreceptors. At 2 weeks after surgery, the numbers of residual host cone photoreceptors outside the graft zone were quantified following specific labelling. Examination of operated retinas revealed highly significantly greater numbers of surviving cones (mean of 38% more at 2 weeks) within the central field compared to sham-operated paired control retinas (p < 0.01). These are the first quantified data indicating a trophic effect of transplanted photoreceptors upon host cone cells. As cone cells are responsible for high acuity and colour vision, such data could have important implications not only for eventual therapeutic approaches to human retinal degenerations but also to understanding underlying interactions between retinal photoreceptors.
Cone cell-specific genes expressed in retinoblastoma
Retinoblastoma, an intraocular tumor that occurs in children, has long been regarded, on the basis of morphological criteria, as a malignancy of the photoreceptor cell lineage. Here it is shown that when this tumor is grown in vitro, the cells express highly specialized photoreceptor cell genes. Transcripts for the transducin alpha subunit, TC alpha, which is specific to the cone cell, as well as transcripts for the red or green cone cell photopigment, were found in seven out of seven low-passage retinoblastoma cell lines. No marker genes specific to rod cell were expressed, suggesting that retinoblastoma has a cone cell lineage.
Suppression of neurite elongation and growth cone motility by electrical activity
Electrical activity may regulate a number of neuronal functions in addition to its role in transmitting signals along nerve cells. The hypothesis that electrical activity affects neurite elongation in sprouting neurons was tested by stimulating individual snail neurons isolated in cell culture. The findings demonstrated that growth cone advance, and thus neurite elongation, is reversibly stopped during periods when action potentials are experimentally evoked. A decrease in filopodial number and growth cone area was also observed. Thus, action potentials can mediate the cessation of neurite outgrowth and thereby may influence structure and connectivity within the nervous system.
Expression of Cone-Photoreceptor–Specific Antigens in a Cell Line Derived from Retinal Tumors in Transgenic Mice
Examined an immortalized mouse retinal cell line (661W) for markers characteristic of photoreceptor cells and validate its photoreceptor origin.661W cells demonstrate cellular and biochemical characteristics exhibited by cone photoreceptor cells. These cells also resemble neuronal cells with their spindlelike processes and should serve as a useful alternative in vitro model for the study of cone photoreceptor cell biology and associated diseases.
Phototransduction by Retinal Ganglion Cells That Set the Circadian Clock
Light synchronizes mammalian circadian rhythms with environmental time by modulating retinal input to the circadian pacemaker—the suprachiasmatic nucleus (SCN) of the hypothalamus. Such photic entrainment requires neither rods nor cones, the only known retinal photoreceptors. Here, we show that retinal ganglion cells innervating the SCN are intrinsically photosensitive. Unlike other ganglion cells, they depolarized in response to light even when all synaptic input from rods and cones was blocked. The sensitivity, spectral tuning, and slow kinetics of this light response matched those of the photic entrainment mechanism, suggesting that these ganglion cells may be the primary photoreceptors for this system.
Müller Cell Outgrowth after Retinal Detachment: Association with Cone Photoreceptors
The growth of Müller cell processes into the subretinal space forms a fibrotic layer that completely inhibits the regeneration of outer segments. The current results show that there appears to be a highly specific interaction between growing Müller cell processes and cone photoreceptors during the earliest phase in this process.
Progressive Loss of Cones in Achromatopsia: An Imaging Study Using Spectral-Domain Optical Coherence Tomography
ACHM( Achromatopsia) is not a stationary disease. The first signs of cone cell loss occur in early childhood. If intervention becomes available in the future, the present results imply that it should be applied in the first decade.
Identification of the RPE65 Protein in Mammalian Cone Photoreceptors
RPE65( retinal pigment epithelium) is expressed in mammalian cones, but not in rods. These results provide further support for physiological observations that cones may have an alternative retinoid cycle.
Regulation of Nerve Growth Mediated by Inositol 1,4,5-Trisphosphate Receptors in Growth Cones
The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) acts as a Ca2+ release channel on internal Ca2+ stores. Type 1 IP3R (IP3R1) is enriched in growth cones of neurons in chick dorsal root ganglia. Depletion of internal Ca2+ stores and inhibition of IP3 signaling with drugs inhibited neurite extension. Microinjection of heparin, a competitive IP3R blocker, induced neurite retraction. Acute localized loss of function of IP3R1 in the growth cone induced by chromophore-assisted laser inactivation resulted in growth arrest and neurite retraction. IP3-induced Ca2+ release in growth cones appears to have a crucial role in control of nerve growth.