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1.
Nat Commun ; 15(1): 4501, 2024 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-38802354

RESUMO

How the spike output of the retina enables human visual perception is not fully understood. Here, we address this at the sensitivity limit of vision by correlating human visual perception with the spike outputs of primate ON and OFF parasol (magnocellular) retinal ganglion cells in tightly matching stimulus conditions. We show that human vision at its ultimate sensitivity limit depends on the spike output of the ON but not the OFF retinal pathway. Consequently, nonlinear signal processing in the retinal ON pathway precludes perceptual detection of single photons in darkness but enables quantal-resolution discrimination of differences in light intensity.


Assuntos
Estimulação Luminosa , Fótons , Retina , Células Ganglionares da Retina , Animais , Humanos , Células Ganglionares da Retina/fisiologia , Retina/fisiologia , Percepção Visual/fisiologia , Sensibilidades de Contraste/fisiologia , Masculino , Adulto , Feminino , Primatas , Vias Visuais/fisiologia , Macaca mulatta , Visão Ocular/fisiologia
2.
Curr Biol ; 32(13): 2848-2857.e6, 2022 07 11.
Artigo em Inglês | MEDLINE | ID: mdl-35609606

RESUMO

Perception of light in darkness requires no more than a handful of photons, and this remarkable behavioral performance can be directly linked to a particular retinal circuit-the retinal ON pathway. However, the neural limits of shadow detection in very dim light have remained unresolved. Here, we unravel the neural mechanisms that determine the sensitivity of mice (CBA/CaJ) to light decrements at the lowest light levels by measuring signals from the most sensitive ON and OFF retinal ganglion cell types and by correlating their signals with visually guided behavior. We show that mice can detect shadows when only a few photon absorptions are missing among thousands of rods. Behavioral detection of such "quantal" shadows relies on the retinal OFF pathway and is limited by noise and loss of single-photon signals in retinal processing. Thus, in the dim-light regime, light increments and decrements are encoded separately via the ON and OFF retinal pathways, respectively.


Assuntos
Retina , Células Fotorreceptoras Retinianas Bastonetes , Animais , Escuridão , Camundongos , Camundongos Endogâmicos CBA , Estimulação Luminosa , Células Ganglionares da Retina
3.
Neuron ; 107(2): 207-209, 2020 07 22.
Artigo em Inglês | MEDLINE | ID: mdl-32702344

RESUMO

How can fish see tiny underwater prey invisible to human eyes? In this issue of Neuron, Yoshimatsu et al. (2020) show that ultraviolet light and a rich set of fine-tuned anatomical and neural specializations originating in ultraviolet-sensitive cones underlie high-resolution prey-capture behavior in larval zebrafish.


Assuntos
Raios Ultravioleta , Peixe-Zebra , Animais , Humanos , Larva , Células Fotorreceptoras Retinianas Cones , Visão Ocular
4.
Curr Biol ; 30(1): 42-53.e4, 2020 01 06.
Artigo em Inglês | MEDLINE | ID: mdl-31866370

RESUMO

Circadian clocks predictively adjust the physiology of organisms to the day/night cycle. The retina has its own clock, and many diurnal changes in its physiology have been reported. However, their implications for retinal functions and visually guided behavior are largely unresolved. Here, we study the impact of diurnal rhythm on the sensitivity limit of mouse vision. A simple photon detection task allowed us to link well-defined retinal output signals directly to visually guided behavior. We show that visually guided behavior at its sensitivity limit is strongly under diurnal control, reaching the highest sensitivity and stability at night. The diurnal differences in visual sensitivity did not arise in the retina, as assessed by spike recordings from the most sensitive retinal ganglion cell types: ON sustained, OFF sustained, and OFF transient alpha ganglion cells. Instead, we found that mice, as nocturnal animals, use a more efficient search strategy for visual cues at night. Intriguingly, they can switch to the more efficient night strategy even at their subjective day after first having performed the task at night. Our results exemplify that the shape of visual psychometric functions depends robustly on the diurnal state of the animal, its search strategy, and even its diurnal history of performing the task. The results highlight the impact of the day/night cycle on high-level sensory processing, demonstrating a direct diurnal impact on the behavioral strategy of the animal.


Assuntos
Ritmo Circadiano , Melatonina/deficiência , Movimento , Células Ganglionares da Retina/fisiologia , Visão Ocular/fisiologia , Animais , Relógios Circadianos , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL
5.
Neuron ; 104(3): 576-587.e11, 2019 11 06.
Artigo em Inglês | MEDLINE | ID: mdl-31519460

RESUMO

All sensory information is encoded in neural spike trains. It is unknown how the brain utilizes this neural code to drive behavior. Here, we unravel the decoding rules of the brain at the most elementary level by linking behavioral decisions to retinal output signals in a single-photon detection task. A transgenic mouse line allowed us to separate the two primary retinal outputs, ON and OFF pathways, carrying information about photon absorptions as increases and decreases in spiking, respectively. We measured the sensitivity limit of rods and the most sensitive ON and OFF ganglion cells and correlated these results with visually guided behavior using markerless head and eye tracking. We show that behavior relies only on the ON pathway even when the OFF pathway would allow higher sensitivity. Paradoxically, behavior does not rely on the spike code with maximal information but instead relies on a decoding strategy based on increases in spiking.


Assuntos
Potenciais de Ação , Comportamento Animal/fisiologia , Retina/fisiologia , Células Ganglionares da Retina/fisiologia , Células Fotorreceptoras Retinianas Bastonetes/fisiologia , Limiar Sensorial/fisiologia , Visão Ocular/fisiologia , Animais , Medições dos Movimentos Oculares , Camundongos , Camundongos Transgênicos
6.
Nat Commun ; 8(1): 1813, 2017 11 27.
Artigo em Inglês | MEDLINE | ID: mdl-29180667

RESUMO

Rod and cone photoreceptors support vision across large light intensity ranges. Rods, active under dim illumination, are thought to saturate at higher (photopic) irradiances. The extent of rod saturation is not well defined; some studies report rod activity well into the photopic range. Using electrophysiological recordings from retina and dorsal lateral geniculate nucleus of cone-deficient and visually intact mice, we describe stimulus and physiological factors that influence photopic rod-driven responses. We find that rod contrast sensitivity is initially strongly reduced at high irradiances, but progressively recovers to allow responses to moderate contrast stimuli. Surprisingly, rods recover faster at higher light levels. A model of rod phototransduction suggests that phototransduction gain adjustments and bleaching adaptation underlie rod recovery. Consistently, exogenous chromophore reduces rod responses at bright background. Thus, bleaching adaptation renders mouse rods responsive to modest contrast at any irradiance. Paradoxically, raising irradiance across the photopic range increases the robustness of rod responses.


Assuntos
Adaptação Fisiológica , Transdução de Sinal Luminoso/fisiologia , Luz/efeitos adversos , Fotodegradação/efeitos da radiação , Células Fotorreceptoras Retinianas Bastonetes/fisiologia , Animais , Visão de Cores/fisiologia , Corpos Geniculados/fisiologia , Camundongos , Camundongos Transgênicos , Modelos Animais , Estimulação Luminosa , Células Fotorreceptoras Retinianas Cones/fisiologia
7.
Philos Trans R Soc Lond B Biol Sci ; 372(1717)2017 Apr 05.
Artigo em Inglês | MEDLINE | ID: mdl-28193818

RESUMO

Visually guided behaviour at its sensitivity limit relies on single-photon responses originating in a small number of rod photoreceptors. For decades, researchers have debated the neural mechanisms and noise sources that underlie this striking sensitivity. To address this question, we need to understand the constraints arising from the retinal output signals provided by distinct retinal ganglion cell types. It has recently been shown in the primate retina that On and Off parasol ganglion cells, the cell types likely to underlie light detection at the absolute visual threshold, differ fundamentally not only in response polarity, but also in the way they handle single-photon responses originating in rods. The On pathway provides the brain with a thresholded, low-noise readout and the Off pathway with a noisy, linear readout. We outline the mechanistic basis of these different coding strategies and analyse their implications for detecting the weakest light signals. We show that high-fidelity, nonlinear signal processing in the On pathway comes with costs: more single-photon responses are lost and their propagation is delayed compared with the Off pathway. On the other hand, the responses of On ganglion cells allow better intensity discrimination compared with the Off ganglion cell responses near visual threshold.This article is part of the themed issue 'Vision in dim light'.


Assuntos
Mamíferos/fisiologia , Retina/fisiologia , Visão Ocular , Vias Visuais , Percepção Visual , Animais , Mamíferos/psicologia , Modelos Biológicos , Estimulação Luminosa
8.
Curr Biol ; 26(6): R231-3, 2016 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-27003884

RESUMO

A new study shows that moth vision trades speed and resolution for contrast sensitivity at night. These remarkable neural adaptations take place in the higher-order neurons of the hawkmoth motion vision pathway and allow the insects to see during night flights.


Assuntos
Mariposas , Visão Ocular , Animais , Sensibilidades de Contraste , Manduca , Neurociências
9.
J Biol Rhythms ; 30(4): 351-4, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26017927

RESUMO

The retina drives various non-image-forming photoresponses, including circadian photoentrainment and pupil constriction. Previous investigators showed that in humans, photic suppression of the clock-controlled hormone melatonin is most sensitive to 460-nm blue light, with a threshold of ~12 log photons cm(-2) s(-1). This threshold is surprising because non-image-forming vision is mediated by intrinsically photosensitive retinal ganglion cells, which receive rod-driven synaptic input and can respond to light levels as low as ~7 log photons cm(-2) s(-1). Using a protocol that enhances data precision, we have found the threshold for human melatonin suppression to be ~10 log photons cm(-2) s(-1) at 460 nm. This finding has far-reaching implications since there is mounting evidence that nocturnal activation of the circadian system can be harmful.


Assuntos
Ritmo Circadiano/fisiologia , Luz/efeitos adversos , Melatonina/metabolismo , Humanos , Estimulação Luminosa , Pupila/fisiologia , Retina/fisiologia , Células Ganglionares da Retina/fisiologia , Opsinas de Bastonetes/fisiologia , Visão Ocular/fisiologia
10.
Curr Biol ; 24(24): 2888-98, 2014 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-25454583

RESUMO

BACKGROUND: Vision in starlight relies on our ability to detect single absorbed photons. Indeed, the sensitivity of dark-adapted vision approaches limits set by the quantal nature of light. This sensitivity requires neural mechanisms that selectively transmit quantal responses and suppress noise. Such mechanisms face an inevitable tradeoff because signal and noise cannot be perfectly separated, and rejecting noise also means rejecting signal. RESULTS: We report measurements of single-photon responses in the output signals of the primate retina. We find that visual signals arising from a few absorbed photons are read out fundamentally differently by primate On and Off parasol ganglion cells, key retinal output neurons. Off parasol cells respond linearly to near-threshold flashes, retaining sensitivity to each absorbed photon but maintaining a high level of noise. On parasol cells respond nonlinearly due to thresholding of their excitatory synaptic inputs. This nonlinearity reduces neural noise but also limits information about single-photon absorptions. CONCLUSIONS: The long-standing idea that information about each photon absorption is available for behavior at the sensitivity limit of vision is not universally true across retinal outputs. More generally, our work shows how a neural circuit balances the competing needs for sensitivity and noise rejection.


Assuntos
Macaca fascicularis/fisiologia , Macaca nemestrina/fisiologia , Fótons , Retina/fisiologia , Transmissão Sináptica , Visão Ocular , Animais , Células Ganglionares da Retina/fisiologia , Células Fotorreceptoras Retinianas Bastonetes/fisiologia
11.
Nat Neurosci ; 14(10): 1309-16, 2011 Sep 18.
Artigo em Inglês | MEDLINE | ID: mdl-21926983

RESUMO

Transduction and synaptic noise generated in retinal cone photoreceptors determine the fidelity with which light inputs are encoded, and the readout of cone signals by downstream circuits determines whether this fidelity is used for vision. We examined the effect of cone noise on visual signals by measuring its contribution to correlated noise in primate retinal ganglion cells. Correlated noise was strong in the responses of dissimilar cell types with shared cone inputs. The dynamics of cone noise could account for rapid correlations in ganglion cell activity, and the extent of shared cone input could explain correlation strength. Furthermore, correlated noise limited the fidelity with which visual signals were encoded by populations of ganglion cells. Thus, a simple picture emerges: cone noise, traversing the retina through diverse pathways, accounts for most of the noise and correlations in the retinal output and constrains how higher centers exploit signals carried by parallel visual pathways.


Assuntos
Potenciais de Ação/fisiologia , Retina/citologia , Células Fotorreceptoras Retinianas Cones/fisiologia , Células Ganglionares da Retina/fisiologia , Vias Visuais/fisiologia , Potenciais de Ação/efeitos dos fármacos , Animais , Fenômenos Biofísicos/efeitos dos fármacos , Fenômenos Biofísicos/fisiologia , Biofísica , Dendritos/ultraestrutura , Estimulação Elétrica/métodos , Fármacos Atuantes sobre Aminoácidos Excitatórios/farmacologia , Macaca , Modelos Neurológicos , Técnicas de Patch-Clamp , Estimulação Luminosa/métodos , Células Fotorreceptoras Retinianas Cones/classificação , Células Fotorreceptoras Retinianas Cones/efeitos dos fármacos , Células Ganglionares da Retina/classificação , Células Ganglionares da Retina/citologia , Células Ganglionares da Retina/efeitos dos fármacos , Estatística como Assunto , Vias Visuais/efeitos dos fármacos
12.
Science ; 332(6035): 1307-12, 2011 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-21659602

RESUMO

Vision begins with photoisomerization of visual pigments. Thermal energy can complement photon energy to drive photoisomerization, but it also triggers spontaneous pigment activation as noise that interferes with light detection. For half a century, the mechanism underlying this dark noise has remained controversial. We report here a quantitative relation between a pigment's photoactivation energy and its peak-absorption wavelength, λ(max). Using this relation and assuming that pigment activations by light and heat go through the same ground-state isomerization energy barrier, we can predict the relative noise of diverse pigments with multi-vibrational-mode thermal statistics. The agreement between predictions and our measurements strongly suggests that pigment noise arises from canonical isomerization. The predicted high noise for pigments with λ(max) in the infrared presumably explains why they apparently do not exist in nature.


Assuntos
Transdução de Sinal Luminoso , Pigmentos da Retina/fisiologia , Ambystoma , Animais , Bufo marinus , Carpa Dourada , Temperatura Alta , Técnicas In Vitro , Luz , Camundongos , Camundongos Endogâmicos C57BL , Fótons , Células Fotorreceptoras Retinianas Cones/fisiologia , Pigmentos da Retina/química , Pigmentos da Retina/efeitos da radiação , Rodopsina/fisiologia
13.
J Gen Physiol ; 134(2): 137-50, 2009 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-19635855

RESUMO

Cone photoreceptors of the vertebrate retina terminate their response to light much faster than rod photoreceptors. However, the molecular mechanisms underlying this rapid response termination in cones are poorly understood. The experiments presented here tested two related hypotheses: first, that the rapid decay rate of metarhodopsin (Meta) II in red-sensitive cones depends on interactions between the 9-methyl group of retinal and the opsin part of the pigment molecule, and second, that rapid Meta II decay is critical for rapid recovery from saturation of red-sensitive cones after exposure to bright light. Microspectrophotometric measurements of pigment photolysis, microfluorometric measurements of retinol production, and single-cell electrophysiological recordings of flash responses of salamander cones were performed to test these hypotheses. In all cases, cones were bleached and their visual pigment was regenerated with either 11-cis retinal or with 11-cis 9-demethyl retinal, an analogue of retinal lacking the 9-methyl group. Meta II decay was four to five times slower and subsequent retinol production was three to four times slower in red-sensitive cones lacking the 9-methyl group of retinal. This was accompanied by a significant slowing of the recovery from saturation in cones lacking the 9-methyl group after exposure to bright (>0.1% visual pigment photoactivated) but not dim light. A mathematical model of the turn-off process of phototransduction revealed that the slower recovery of photoresponse can be explained by slower Meta decay of 9-demethyl visual pigment. These results demonstrate that the 9-methyl group of retinal is required for steric chromophore-opsin interactions that favor both the rapid decay of Meta II and the rapid response recovery after exposure to bright light in red-sensitive cones.


Assuntos
Transdução de Sinal Luminoso/fisiologia , Células Fotorreceptoras Retinianas Cones/fisiologia , Retinaldeído/química , Rodopsina/metabolismo , Animais , Eletrofisiologia , Cinética , Microespectrofotometria , Modelos Teóricos , Opsinas/química , Opsinas/metabolismo , Células Fotorreceptoras Retinianas Cones/química , Células Fotorreceptoras Retinianas Cones/metabolismo , Urodelos
14.
J Biol Chem ; 284(24): 16492-16500, 2009 Jun 12.
Artigo em Inglês | MEDLINE | ID: mdl-19386593

RESUMO

11-cis-retinol has previously been shown in physiological experiments to promote dark adaptation and recovery of photoresponsiveness of bleached salamander red cones but not of bleached salamander red rods. The purpose of this study was to evaluate the direct interaction of 11-cis-retinol with expressed human and salamander cone opsins, and to determine by microspectrophotometry pigment formation in isolated salamander photoreceptors. We show here in a cell-free system using incorporation of radioactive guanosine 5'-3-O-(thio)triphosphate into transducin as an index of activity, that 11-cis-retinol inactivates expressed salamander cone opsins, acting an inverse agonist. Similar results were obtained with expressed human red and green opsins. 11-cis-retinol had no significant effect on the activity of human blue cone opsin. In contrast, 11-cis-retinol activates the expressed salamander and human red rod opsins, acting as an agonist. Using microspectrophotometry of salamander cone photoreceptors before and after bleaching and following subsequent treatment with 11-cis-retinol, we show that 11-cis-retinol promotes pigment formation. Pigment was not formed in salamander red rods or green rods (containing the same opsin as blue cones) treated under the same conditions. These results demonstrate that 11-cis-retinol is not a useful substrate for rod photoreceptors although it is for cone photoreceptors. These data support the premise that rods and cones have mechanisms for handling retinoids and regenerating visual pigment that are specific to photoreceptor type. These mechanisms are critical to providing regenerated pigments in a time scale required for the function of these two types of photoreceptors.


Assuntos
Opsinas dos Cones/agonistas , Opsinas dos Cones/metabolismo , Células Fotorreceptoras Retinianas Cones/efeitos dos fármacos , Células Fotorreceptoras Retinianas Cones/metabolismo , Vitamina A/farmacologia , Vitaminas/farmacologia , Ambystoma , Animais , Sistema Livre de Células , Adaptação à Escuridão/efeitos dos fármacos , Adaptação à Escuridão/fisiologia , Agonismo Inverso de Drogas , Humanos , Epitélio Pigmentado da Retina/metabolismo , Células Fotorreceptoras Retinianas Bastonetes/efeitos dos fármacos , Células Fotorreceptoras Retinianas Bastonetes/metabolismo , Opsinas de Bastonetes/metabolismo
15.
J Physiol ; 585(Pt 1): 57-74, 2007 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-17884920

RESUMO

Dark noise, light-induced noise and responses to brief flashes of light were recorded in the membrane current of isolated rods from larval tiger salamander retina before and after bleaching most of the native visual pigment, which mainly has the 11-cis-3,4-dehydroretinal (A2) chromophore, and regenerating with the 11-cis-retinal (A1) chromophore in the same isolated rods. The purpose was to test the hypothesis that blue-shifting the pigment by switching from A2 to A1 will decrease the rate of spontaneous thermal activations and thus intrinsic light-like noise in the rod. Complete recordings were obtained in five cells (21 degrees C). Based on the wavelength of maximum absorbance, lambda max,A1 = 502 nm and lambda max,A2 = 528 nm, the average A2 : A1 ratio determined from rod spectral sensitivities and absorbances was approximately 0.74 : 0.26 in the native state and approximately 0.09 : 0.91 in the final state. In the native (A2) state, the single-quantum response (SQR) had an amplitude of 0.41 +/- 0.03 pA and an integration time of 3.16 +/- 0.15 s (mean +/- s.e.m.). The low-frequency branch of the dark noise power spectrum was consistent with discrete SQR-like events occurring at a rate of 0.238 +/- 0.026 rod(-1) s(-1). The corresponding values in the final state were 0.57 +/- 0.07 pA (SQR amplitude), 3.47 +/- 0.26 s (SQR integration time), and 0.030 +/- 0.006 rod(-1) s(-1) (rate of dark events). Thus the rate of dark events per rod and the fraction of A2 pigment both changed by ca 8-fold between the native and final states, indicating that the dark events originated mainly in A2 molecules even in the final state. By extrapolating the linear relation between event rates and A2 fraction to 0% A2 (100% A1) and 100% A2 (0% A1), we estimated that the A1 pigment is at least 36 times more stable than the A2 pigment. The noise component attributed to discrete dark events accounted for 73% of the total dark current variance in the native (A2) state and 46% in the final state. The power spectrum of the remaining 'continuous' noise component did not differ between the two states. The smaller and faster SQR in the native (A2) state is consistent with the idea that the rod behaves as if light-adapted by dark events that occur at a rate of nearly one per integration time. Both the decreased level of dark noise and the increased SQR amplitude must significantly improve the reliability of photon detection in dim light in the presence of the A1 chromophore compared to the native (A2) state in salamander rods.


Assuntos
Ambystoma/fisiologia , Escuridão , Pigmentos da Retina/fisiologia , Células Fotorreceptoras Retinianas Bastonetes/fisiologia , Retinaldeído/fisiologia , Animais , Potenciais Evocados Visuais/fisiologia , Luz , Estimulação Luminosa , Fatores de Tempo , Visão Ocular/fisiologia
16.
Vis Neurosci ; 24(3): 389-98, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17822578

RESUMO

Absorbance spectra of rods and some cones were measured by microspectrophotometry in 22 fish species from the brackish-water of the Baltic Sea, and when applicable, in the same species from the Atlantic Ocean (3 spp.), the Mediterranean Sea (1 sp.), or Finnish fresh-water lakes (9 spp.). The main purpose was to study whether there were differences suggesting spectral adaptation of rod vision to different photic environments during the short history (<10(4) years) of postglacial isolation of the Baltic Sea and the Finnish lakes. Rod absorbance spectra of the Baltic subspecies/populations of herring (Clupea harengus membras), flounder (Platichthys flesus), and sand goby (Pomatoschistus minutus) were all long-wavelength-shifted (9.8, 1.9, and 5.3 nm, respectively, at the wavelength of maximum absorbance, lambda(max)) compared with their truly marine counterparts, consistent with adaptation for improved quantum catch, and improved signal-to-noise ratio of vision in the Baltic light environment. Judged by the shape of the spectra, the chromophore was pure A1 in all these cases; hence the differences indicate evolutionary tuning of the opsin. In no species of fresh-water origin did we find significant opsin-based spectral shifts specific to the Baltic populations, only spectral differences due to varying A1/A2 chromophore ratio in some. For most species, rod lambda(max) fell within a wavelength range consistent with high signal-to-noise ratio of vision in the spectral conditions prevailing at depths where light becomes scarce in the respective waters. Exceptions were sandeels in the Baltic Sea, which are active only in bright light, and all species in a "brown" lake, where rod lambda(max) lay far below the theoretically optimal range.


Assuntos
Peixes/metabolismo , Especiação Genética , Pigmentos da Retina/metabolismo , Animais , Peixes/classificação , Microespectrofotometria/métodos , Oceanos e Mares , Células Fotorreceptoras de Vertebrados , Células Fotorreceptoras Retinianas Cones/citologia , Células Fotorreceptoras Retinianas Cones/metabolismo , Células Fotorreceptoras Retinianas Bastonetes/citologia , Células Fotorreceptoras Retinianas Bastonetes/metabolismo
18.
J Gen Physiol ; 128(6): 671-85, 2006 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-17101818

RESUMO

Our ability to see in bright light depends critically on the rapid rate at which cone photoreceptors detect and adapt to changes in illumination. This is achieved, in part, by their rapid response termination. In this study, we investigate the hypothesis that this rapid termination of the response in red cones is dependent on interactions between the 9-methyl group of retinal and red cone opsin, which are required for timely metarhodopsin (Meta) II decay. We used single-cell electrical recordings of flash responses to assess the kinetics of response termination and to calculate guanylyl cyclase (GC) rates in salamander red cones containing native visual pigment as well as visual pigment regenerated with 11-cis 9-demethyl retinal, an analogue of retinal in which the 9-methyl group is missing. After exposure to bright light that photoactivated more than approximately 0.2% of the pigment, red cones containing the analogue pigment had a slower recovery of both flash response amplitudes and GC rates (up to 10 times slower at high bleaches) than red cones containing 11-cis retinal. This finding is consistent with previously published biochemical data demonstrating that red cone opsin regenerated in vitro with 11-cis 9-demethyl retinal exhibited prolonged activation as a result of slowed Meta II decay. Our results suggest that two different mechanisms regulate the recovery of responsiveness in red cones after exposure to light. We propose a model in which the response recovery in red cones can be regulated (particularly at high light intensities) by the Meta II decay rate if that rate has been inhibited. In red cones, the interaction of the 9-methyl group of retinal with opsin promotes efficient Meta II decay and, thus, the rapid rate of recovery.


Assuntos
Células Fotorreceptoras Retinianas Cones/fisiologia , Retinaldeído/análogos & derivados , 1-Metil-3-Isobutilxantina/farmacologia , Ambystoma , Animais , Adaptação à Escuridão , Guanilato Ciclase/metabolismo , Cinética , Células Fotorreceptoras/fisiologia , Retinaldeído/fisiologia , Rodopsina/metabolismo , Espectrofotometria
19.
J Gen Physiol ; 128(2): 153-69, 2006 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-16847097

RESUMO

The visual cycle is a chain of biochemical reactions that regenerate visual pigment following exposure to light. Initial steps, the liberation of all-trans retinal and its reduction to all-trans retinol by retinol dehydrogenase (RDH), take place in photoreceptors. We performed comparative microspectrophotometric and microfluorometric measurements on a variety of rod and cone photoreceptors isolated from salamander retinae to correlate the rates of photoproduct decay and retinol production. Metapigment decay rate was spatially uniform within outer segments and 50-70 times faster in the cells that contained cone-type pigment (SWS2 and M/LWS) compared to cells with rod-type pigment (RH1). Retinol production rate was strongly position dependent, fastest at the base of outer segments. Retinol production rate was 10-40 times faster in cones with cone pigments (SWS2 and M/LWS) than in the basal OS of rods containing rod pigment (RH1). Production rate was approximately five times faster in rods containing cone pigment (SWS2) than the rate in basal OS of rods containing the rod pigment (RH1). We show that retinol production is defined either by metapigment decay rate or RDH reaction rate, depending on cell type or outer segment region, whereas retinol removal is defined by the surface-to-volume ratio of the outer segment and the availability of retinoid binding protein (IRBP). The more rapid rates of retinol production in cones compared to rods are consistent with the more rapid operation of the visual cycle in these cells.


Assuntos
Células Fotorreceptoras de Vertebrados/metabolismo , Pigmentos da Retina/metabolismo , Vitamina A/metabolismo , Ambystoma , Animais , Proteínas do Olho/farmacologia , Cinética , Microscopia de Fluorescência , Microespectrofotometria , Fotodegradação , Células Fotorreceptoras de Vertebrados/citologia , Células Fotorreceptoras de Vertebrados/efeitos dos fármacos , Células Fotorreceptoras Retinianas Cones/citologia , Células Fotorreceptoras Retinianas Cones/efeitos dos fármacos , Células Fotorreceptoras Retinianas Cones/metabolismo , Células Fotorreceptoras Retinianas Bastonetes/citologia , Células Fotorreceptoras Retinianas Bastonetes/efeitos dos fármacos , Células Fotorreceptoras Retinianas Bastonetes/metabolismo , Retinaldeído/metabolismo , Proteínas de Ligação ao Retinol/farmacologia , Rodopsina/metabolismo , Fatores de Tempo
20.
Artigo em Inglês | MEDLINE | ID: mdl-16010556

RESUMO

We report the first study of the relation between the wavelength of maximum absorbance (lambdamax) and the photoactivation energy (Ea) in invertebrate visual pigments. Two populations of the opossum shrimp Mysis relicta were compared. The two have been separated for 9,000 years and have adapted to different spectral environments ("Sea" and "Lake") with porphyropsins peaking at lambdamax=529 nm and 554 nm, respectively. The estimation of Ea was based on measurement of temperature effects on the spectral sensitivity of the eye. In accordance with theory (Stiles in Transactions of the optical convention of the worshipful company of spectacle makers. Spectacle Makers' Co., London, 1948), relative sensitivity to long wavelengths increased with rising temperature. The estimates calculated from this effect are Ea,529=47.8+/-1.8 kcal/mol and Ea,554=41.5+/-0.7 kcal/mol (different at P<0.01). Thus the red-shift of lambdamax in the "Lake" population, correlating with the long-wavelength dominated light environment, is achieved by changes in the opsin that decrease the energy gap between the ground state and the first excited state of the chromophore. We propose that this will carry a cost in terms of increased thermal noise, and that evolutionary adaptation of the visual pigment to the light environment is directed towards maximizing the signal-to-noise ratio rather than the quantum catch.


Assuntos
Luz , Pigmentos da Retina/fisiologia , Pigmentos da Retina/efeitos da radiação , Animais , Crustáceos , Especificidade da Espécie , Espectrofotometria/métodos , Temperatura
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