My rods and cones are all screwed up!

The mammalian retina is known to contain two distinct transducins that interact with their respective rod and cone pigments. However, there are no reports of a nonmammalian species having two distinct transducins. In the present study, we report the cloning and cellular localization of two transducin α subunits (Gαt) from the tiger salamander. Through degenerate polymerase chain reaction (PCR) and subsequent screening of a salamander retina cDNA library, we have identified two forms of Gαt. When compared to existing sequences in GenBank, the cloned subunits showed high similarity to rod and cone transducins. The salamander Gαt-1 has 91.2–93.7% amino acid sequence identity to mammalian rod Gαt subunits and 79.7–80.9% to mammalian cone Gαts. The salamander Gαt-2 has 86.2–87.9% sequence identity to mammalian cone Gαts and 78.9–80.9% to mammalian rod Gαts at the amino acid level. The Gαt-1 cDNA encodes 350 amino acids while the Gαt-2 cDNA encodes 354 residues, which is typical for rod and cone Gαts, respectively, and we thus identified the Gαt-1 as rod and Gαt-2 as cone Gαt. Sequences identified as effector binding sites and GTPase activity regions are highly conserved between the two subunits. Genomic Southern blot analysis showed that rod and cone Gαt subunits are both encoded by single-copy genes. Northern blot analysis identified retina-specific transcripts of 3.0 kb for rod Gαt and 2.6 kb for cone Gαt. Immunohistochemistry in the flat-mounted salamander retina demonstrated that rod Gαt is localized to rods, predominantly in the outer segments; similarly, cone Gαt is localized to cone outer segments. The results confirm that the two sequences encode rod and cone transducins and demonstrate that this lower vertebrate contains two distinct transducins that are localized specifically to rod and cone photoreceptors.

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ELECTRON MICROSCOPE OBSERVATIONS ON SYNAPTIC VESICLES IN SYNAPSES OF THE RETINAL RODS AND CONES

The Journal of Cell Biology ◽

10.1083/jcb.2.3.307 ◽

1956 ◽

Vol 2 (3) ◽

pp. 307-318 ◽

Cited By ~ 117

Author(s):

Eduardo De Robertis ◽

Carlos M. Franchi

Keyword(s):

Electron Microscope ◽

Synaptic Vesicles ◽

Sharp Decrease ◽

Albino Rabbit ◽

Synaptic Membrane ◽

Complete Darkness ◽

Rods And Cones ◽

Retinal Rods ◽

Filamentous Material ◽

Rod Cell

The submicroscopic organization of the rod and cone synapses of the albino rabbit has been investigated with the use of the electron microscope. The most common rod synapse consists of an enlarged expansion of the rod fiber (the so called spherule) into which the dendritic postsynaptic fiber of the bipolar cell penetrates and digitates. The membrane surrounding the terminal consists of a double layer, the external of which is interpreted as belonging to the intervening glial cells. The synaptic membrane has a pre- and a postsynaptic layer with a total thickness of 180 to 300 A. The presynaptic layer is frequently denser and is intimately associated with the adjacent synaptic vesicles. The synaptic membrane shows processes constituted by foldings of the presynaptic layer. The entire spherule is filled with synaptic vesicles varying in diameter between 200 and 650 A with a mean of 386 A. In addition, the spherule contains a few large vacuoles near the rod fiber, interpreted as endoplasmic reticulum, and a matrix in which with high resolution a fine filamentous material can be observed. The postsynaptic fiber is homogeneous and usually does not show synaptic vesicles. In animals maintained in complete darkness for 24 hours vesicles appear to accumulate near the synaptic membrane and its processes. After 9 days there is a sharp decrease in size of the synaptic vesicles. A special rod synapse in which the dendritic postsynaptic expansion penetrates directly into the rod cell body has been identified. In line with Cajal's classification this type of synapse could be considered as a somatodendritic one. The cone synapse has a much larger terminal with a more complex relationship with the postsynaptic fiber. However, the same components recognized in the rod synapse can be observed. In animals maintained for 9 days in complete darkness there is also a considerable diminution in size of the synaptic vesicles.

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Fundamentals of circadian entrainment by light

Lighting Research and Technology ◽

10.1177/14771535211014792 ◽

2021 ◽

Vol 53 (5) ◽

pp. 377-393

Author(s):

RG Foster

Keyword(s):

Ganglion Cells ◽

Light Exposure ◽

Bright Light ◽

Evidence Based ◽

Retinal Ganglion ◽

Rods And Cones ◽

Long Duration ◽

Lighting Systems ◽

Short Wavelength Light ◽

Wavelength Light

Light at dawn and dusk is the key signal for the entrainment of the circadian clock. Light at dusk delays the clock. Light at dawn advances the clock. The threshold for human entrainment requires relatively bright light for a long duration, but the precise irradiance/duration relationships for photoentrainment have yet to be fully defined. Photoentrainment is achieved by a network of photosensitive retinal ganglion cells (pRGCs) which utilise the short-wavelength light-sensitive photopigment, melanopsin. Although rods and cones are not required, they do play a role in photoentrainment, by projecting to and modulating the endogenous photosensitivity of the pRGCs, but in a manner that remains poorly understood. It is also important to emphasise that the age and prior light exposure of an individual will modify the efficacy of entrainment stimuli. Because of the complexity of photoreceptor interactions, attempts to develop evidence-based human centric lighting are not straightforward. We need to study how humans respond to dynamic light exposure in the ‘real world’ where light intensity, duration, spectral quality and the time of exposure vary greatly. Defining these parameters will allow the development of electric lighting systems that will enhance human circadian entrainment.

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Visual Pigments in Single Rods and Cones of the Human Retina

Science ◽

10.1126/science.144.3614.45 ◽

1964 ◽

Vol 144 (3614) ◽

pp. 45-52 ◽

Cited By ~ 299

Author(s):

P. K. Brown ◽

G. Wald

Keyword(s):

Visual Pigments ◽

Human Retina ◽

Rods And Cones

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Properties of synaptic transmission from photoreceptors to bipolar cells in the mudpuppy retina

Journal of Neurophysiology ◽

10.1152/jn.1993.69.2.352 ◽

1993 ◽

Vol 69 (2) ◽

pp. 352-360 ◽

Cited By ~ 17

Author(s):

H. G. Kim ◽

R. F. Miller

Keyword(s):

Kynurenic Acid ◽

Response Times ◽

Plexiform Layer ◽

Bipolar Cells ◽

Slice Preparation ◽

Peak Response ◽

Rods And Cones ◽

Significant Difference ◽

Pharmacological Studies ◽

Whole Cell Recordings

1. Simultaneous, whole-cell recordings were obtained from synaptically coupled photoreceptor/bipolar cell pairs, by the use of direct visualization in a superfused, mudpuppy retinal slice preparation. 2. OFF-bipolar cells (BPs) generated sign-conserving responses when extrinsic current was injected into rods and cones, whereas ON-BPs generated a sign-reversing response. OFF-BPs (n = 24) responded faster than ON-BPs (n = 12), in terms of response latency (27.8 vs. 80.6 ms) and peak response times (50.5 vs. 159.8 ms) when current was injected into photoreceptors. We did not detect any significant difference between rod- versus cone-mediated latency or peak response times in the ON- and OFF-BP subtypes. 3. Rod and cone inputs to OFF-BPs were blocked by kynurenic acid (Kyn), but the doses required were significantly higher for rod inputs: the IC50 (the concentration at which an antagonist blocks 50% of the responses) for Kyn was 0.3 mM for cone inputs and 1 mM for rod inputs. 4. Rod inputs to OFF-BPs showed the same Kyn sensitivity as rod inputs to horizontal cells (HCs). However, cone inputs to HCs (IC50 < 200 microM) were more sensitive to Kyn than those to OFF-BPs. 5. The pharmacological studies presented here, together with previous studies, suggest that the sign-conserving pathway in the outer plexiform layer of the mudpuppy retina involves at least three subtypes of glutamate receptors: 1) cone-activated receptors of HCs; 2) cone-activated receptors of OFF-BPs; and 3) rod-activated receptors found in HCs and BPs.(ABSTRACT TRUNCATED AT 250 WORDS)

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Spectral absorbance, structure, and population density of photoreceptors in the retina of the lake sturgeon (Acipenser fulvescens)

Canadian Journal of Zoology ◽

10.1139/z07-033 ◽

2007 ◽

Vol 85 (4) ◽

pp. 584-587 ◽

Cited By ~ 4

Author(s):

A.J. Sillman ◽

E.K. Ong ◽

E.R. Loew

Keyword(s):

Visual Pigment ◽

Visual Pigments ◽

Lake Sturgeon ◽

Acipenser Fulvescens ◽

Long Wavelength ◽

Rods And Cones ◽

The North ◽

Spectral Absorbance ◽

Dim Light ◽

Scanning Electron

Lake sturgeon ( Acipenser fulvescens Rafinesque, 1817) photoreceptors were studied with scanning electron microscopy and microspectrophotometry. The retina contains both rods and cones, with cones estimated composing about 30% of the photoreceptor population. Only large single cones were identified and they are similar to those found in other species of the order Acipenseriformes. The rods are large, with long, broad outer segments, and are similar to the dominant rod found in other sturgeons and the North American paddlefish ( Polyodon spathula (Walbaum, 1792)). Mean (SD) rod packing density at 22 624 ± 3 509 rods/mm2 is low compared with those of other animals that function primarily in dim light. The visual pigment of the rods has a mean (SD) peak absorbance (λmax) at 541 ± 2 nm. Three different cone populations were identified: a long wavelength sensitive cone containing a visual pigment with λmax at 619 ± 3 nm; middle wavelength sensitive cone with λmax at 538 ± 1 nm; and short wavelength sensitive cone with λmax at 448 ± 1 nm. All the visual pigments are based on the vitamin A2 chromophore.

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Contribution of human melanopsin retinal ganglion cells to steady-state pupil responses

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2010.0330 ◽

2010 ◽

Vol 277 (1693) ◽

pp. 2485-2492 ◽

Cited By ~ 56

Author(s):

Sei-ichi Tsujimura ◽

Kazuhiko Ukai ◽

Daisuke Ohama ◽

Atsuo Nuruki ◽

Kazutomo Yunokuchi

Keyword(s):

Steady State ◽

Retinal Ganglion Cells ◽

Ganglion Cells ◽

Pupil Diameter ◽

Retinal Ganglion ◽

Silent Substitution ◽

Conventional View ◽

Rods And Cones ◽

Direct Measurements ◽

Stimulation System

The recent discovery of melanopsin-containing retinal ganglion cells (mRGCs) has led to a fundamental reassessment of non-image forming processing, such as circadian photoentrainment and the pupillary light reflex. In the conventional view of retinal physiology, rods and cones were assumed to be the only photoreceptors in the eye and were, therefore, considered responsible for non-image processing. However, signals from mRGCs contribute to this non-image forming processing along with cone-mediated luminance signals; although both signals contribute, it is unclear how these signals are summed. We designed and built a novel multi-primary stimulation system to stimulate mRGCs independently of other photoreceptors using a silent-substitution technique within a bright steady background. The system allows direct measurements of pupillary functions for mRGCs and cones. We observed a significant change in steady-state pupil diameter when we varied the excitation of mRGC alone, with no change in luminance and colour. Furthermore, the change in pupil diameter induced by mRGCs was larger than that induced by a variation in luminance alone: that is, for a bright steady background, the mRGC signals contribute to the pupillary pathway by a factor of three times more than the L- and M-cone signals.

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Photoresponses of Rods and Cones

Adler's Physiology of the Eye ◽

10.1016/b978-0-323-05714-1.00019-4 ◽

2011 ◽

pp. 411-428 ◽

Cited By ~ 2

Author(s):

Peter R. MacLeish ◽

Clint L. Makino

Keyword(s):

Rods And Cones

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