Electrical Coupling between Mammalian Cones

DeVries, Steven H.; Qi, Xiaofeng; Smith, Robert G.; Makous, Walter; Sterling, Peter

doi:10.1016/s0960-9822(02)01261-7

Cited by 137 publications

(127 citation statements)

References 40 publications

(5 reference statements)

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“…This is likely to be the reason why acuity measured with stimuli that are visible to only L or M cones is not worse than acuity based on the entire mosaic (Green, 1968;Cavonius and Estévez, 1975;Williams, 1990;Carroll et al, 2004). A patchy cone arrangement may have the additional advantage in helping to ameliorate the spectral blurring that occurs as a result of electrical coupling between neighboring cones (Hsu et al, 2000;DeVries et al, 2002;Hornstein et al, 2004).…”

Section: Implications Of L/m Cone Arrangement For Visionmentioning

confidence: 99%

Organization of the Human Trichromatic Cone Mosaic

Hofer¹,

Carroll²,

Neitz³

et al. 2005

J. Neurosci.

379

308

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Using high-resolution adaptive-optics imaging combined with retinal densitometry, we characterized the arrangement of short-(S), middle-(M), and long-(L) wavelength-sensitive cones in eight human foveal mosaics. As suggested by previous studies, we found males with normal color vision that varied in the ratio of L to M cones (from 1.1:1 to 16.5:1). We also found a protan carrier with an even more extreme L:M ratio (0.37:1). All subjects had nearly identical S-cone densities, indicating independence of the developmental mechanism that governs the relative numerosity of L/M and S cones. L:M cone ratio estimates were correlated highly with those obtained in the same eyes using the flicker photometric electroretinogram (ERG), although the comparison indicates that the signal from each M cone makes a larger contribution to the ERG than each L cone. Although all subjects had highly disordered arrangements of L and M cones, three subjects showed evidence for departures from a strictly random rule for assigning the L and M cone photopigments. In two retinas, these departures corresponded to local clumping of cones of like type. In a third retina, the L:M cone ratio differed significantly at two retinal locations on opposite sides of the fovea. These results suggest that the assignment of L and M pigment, although highly irregular, is not a completely random process. Surprisingly, in the protan carrier, in which X-chromosome inactivation would favor L-or M-cone clumping, there was no evidence of clumping, perhaps as a result of cone migration during foveal development.

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Section: Implications Of L/m Cone Arrangement For Visionmentioning

confidence: 99%

Organization of the Human Trichromatic Cone Mosaic

Hofer¹,

Carroll²,

Neitz³

et al. 2005

J. Neurosci.

379

308

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“…Photoreceptor coupling is mediated by connexons containing Cx36 [44]. Coupling can improve the signal to noise ratio, extend the dynamic range of the rod synapse, and enhance boundary detection by cones [43,[45][46][47]. Coupling also influences the kinetics of post-synaptic responses by contributing to band pass filtering at rod synapses [48].…”

Section: Photoreceptor Couplingmentioning

confidence: 99%

Kinetics of Synaptic Transmission at Ribbon Synapses of Rods and Cones

Thoreson

2007

Mol Neurobiol

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The ribbon synapse is a specialized structure that allows photoreceptors to sustain the continuous release of vesicles for hours upon hours and years upon years but also respond rapidly to momentary changes in illumination. Light responses of cones are faster than those of rods and, mirroring this difference, synaptic transmission from cones is also faster than transmission from rods. This review evaluates the various factors that regulate synaptic kinetics and contribute to kinetic differences between rod and cone synapses. Presynaptically, the release of glutamate-laden synaptic vesicles is regulated by properties of the synaptic proteins involved in exocytosis, influx of calcium through calcium channels, calcium release from intracellular stores, diffusion of calcium to the release site, calcium buffering, and extrusion of calcium from the cytoplasm. The rate of vesicle replenishment also limits the ability of the synapse to follow changes in release. Post-synaptic factors include properties of glutamate receptors, dynamics of glutamate diffusion through the cleft, and glutamate uptake by glutamate transporters. Thus, multiple synaptic mechanisms help to shape the responses of second-order horizontal and bipolar cells. KeywordsPhotoreceptor; Synaptic transmission; Glutamate; Calcium; Vesicles; Retina Vision begins with the transduction of light into membrane potential changes as the result of an enzymatic cascade occurring in the outer segments of rod and cone photoreceptors [1,2]. Light-evoked membrane potential changes are modified by voltage-dependent currents in the inner segment [3] and transmitted to second order bipolar and horizontal cells by changes in release of the neurotransmitter, L-glutamate, from the synaptic terminals of both rods and cones. Because all of the visual information available to downstream retinal neurons must first pass through the photoreceptor synapse, synaptic transmission from photoreceptors has a considerable impact on visual perception. The focus of this review is on mechanisms that shape the kinetics of synaptic transmission at synapses of rods and cones. Additional information on other physiological and anatomical characteristics of photoreceptor ribbon synapses can be found in recent reviews [4][5][6]. Differences in Rod and Cone KineticsRod and cone photoreceptors are tonically depolarized in darkness with membrane potentials of −35 to −45 mV that allow continuous release of the neurotransmitter, L-glutamate. Light onset causes photoreceptors to hyperpolarize by as much as 30 mV, leading to a reduction in

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“…It is generally believed that patterns of lateral excitation play relevant physiological roles in amplifying the responses of sensory afferents tuned to qualitatively similar stimuli (Herberholz et al, 2002). In contrast to other examples, such as retinal cones (DeVries et al, 2002) and crayfish locomotor networks (el Manira et al, 1993), in which electrical synapses are located between the presynaptic neurons, club endings are electrically coupled to each other through the M-cell lateral dendrite. This coupling arrangement would explain why whereas in some systems junctional properties prevent the antidromic spread of postsynaptically originated currents (Furshpan and Potter, 1959;Auerbach andBennett, 1969: Ringham, 1975;Edwards et al 1991), physiological properties of the club endings actually promote this phenomenon.…”

Section: Functional Significancementioning

confidence: 99%