RESUMO
A17 amacrine cells are an important part of the scotopic pathway. Their synaptic varicosities receive glutamatergic inputs from rod bipolar cells (RBC) and release GABA onto the same RBC terminal, forming a reciprocal feedback that shapes RBC depolarization. Here, using patch-clamp recordings, we characterized electrical coupling between A17 cells of the rat retina and report the presence of strongly interconnected and non-coupled A17 cells. In coupled A17 cells, evoked currents preferentially flow out of the cell through GJs and cross-synchronization of presynaptic signals in a pair of A17 cells is correlated to their coupling degree. Moreover, we demonstrate that stimulation of one A17 cell can induce electrical and calcium transients in neighboring A17 cells, thus confirming a functional flow of information through electrical synapses in the A17 coupled network. Finally, blocking GJs caused a strong decrease in the amplitude of the inhibitory feedback onto RBCs. We therefore propose that electrical coupling between A17 cells enhances feedback onto RBCs by synchronizing and facilitating GABA release from inhibitory varicosities surrounding each RBC axon terminal. GJs between A17 cells are therefore critical in shaping the visual flow through the scotopic pathway.
Assuntos
Células Amácrinas/fisiologia , Células Bipolares da Retina/metabolismo , Animais , Cálcio/metabolismo , Adaptação à Escuridão/fisiologia , Retroalimentação , Feminino , Junções Comunicantes/fisiologia , Masculino , Potenciais da Membrana/efeitos dos fármacos , Visão Noturna/fisiologia , Técnicas de Patch-Clamp , Ratos , Ratos Sprague-Dawley , Receptores de AMPA/metabolismo , Receptores de GABA/metabolismo , Retina/metabolismo , Retina/fisiologia , Células Bipolares da Retina/fisiologia , Células Fotorreceptoras Retinianas Bastonetes/fisiologia , Sinapses/metabolismo , Transmissão Sináptica/fisiologia , Ácido gama-Aminobutírico/metabolismoRESUMO
Unlike all other New World (platyrrine) monkeys, both male and female howler monkeys (Alouatta sp.) are obligatory trichromats. In all other platyrrines, only females can be trichromats, while males are always dichromats, as determined by multiple behavioral, electrophysiological, and genetic studies. In addition to obligatory trichromacy, Alouatta has an unusual fovea, with substantially higher peak cone density in the foveal pit than every other diurnal anthropoid monkey (both platyrrhines and catarrhines) and great ape yet examined, including humans. In addition to documenting the general organization of the retinal ganglion cell layer in Alouatta, the distribution of cones is compared to retinal ganglion cells, to explore possible relationships between their atypical trichromacy and foveal specialization. The number and distribution of retinal ganglion cells and displaced amacrine cells were determined in six flat-mounted retinas from five Alouatta caraya. Ganglion cell density peaked at 0.5 mm between the fovea and optic nerve head, reaching 40,700-45,200 cells/mm2. Displaced amacrine cell density distribution peaked between 0.5-1.75 mm from the fovea, reaching mean values between 2,050-3,100 cells/mm2. The mean number of ganglion cells was 1,133,000±79,000 cells and the mean number of displaced amacrine cells was 537,000±61,800 cells, in retinas of mean area 641±62 mm2. Ganglion cell and displaced amacrine cell density distribution in the Alouatta retina was consistent with that observed among several species of diurnal Anthropoidea, both platyrrhines and catarrhines. The principal alteration in the Alouatta retina appears not to be in the number of any retinal cell class, but rather a marked gradient in cone density within the fovea, which could potentially support high chromatic acuity in a restricted central region.
Assuntos
Células Amácrinas/citologia , Células Ganglionares da Retina/citologia , Alouatta , Células Amácrinas/fisiologia , Animais , Visão de Cores , Masculino , Células Ganglionares da Retina/fisiologiaRESUMO
Motion detection is one of the most important and primitive computations performed by our visual system. Specifically in the retina, ganglion cells producing motion direction-selective responses have been addressed by different disciplines, such as mathematics, neurophysiology and computational modeling, since the beginnings of vision science. Although a number of studies have analyzed theoretical and mathematical considerations for such responses, a clear picture of the underlying cellular mechanisms is only recently emerging. In general, motion direction selectivity is based on a non-linear asymmetric computation inside a receptive field differentiating cell responses between preferred and null direction stimuli. To what extent can biological findings match these considerations? In this review, we outline theoretical and mathematical studies of motion direction selectivity, aiming to map the properties of the models onto the neural circuitry and synaptic connectivity found in the retina. Additionally, we review several compartmental models that have tried to fill this gap. Finally, we discuss the remaining challenges that computational models will have to tackle in order to fully understand the retinal motion direction-selective circuitry.
Assuntos
Modelos Teóricos , Percepção de Movimento/fisiologia , Retina/citologia , Retina/fisiologia , Células Amácrinas/fisiologia , Animais , Humanos , Inibição Neural/fisiologia , Células Ganglionares da Retina/fisiologia , Vias Visuais/citologia , Vias Visuais/fisiologiaRESUMO
INTRODUCTION: Glycine and the gamma-aminobutyric acid are the principal inhibitory neurotransmitters in the vertebrate retina. The inhibitory action of glycine is mediated by the post-synaptic glycine receptor, a chloride-selective channel, constituted by three beta and two alpha subunits (alpha(1)-alpha(4)), which is antagonized by the alkaloid strychnine. In the retina, it is known that all alpha isoforms are expressed at the level of the inner synaptic layer with a very low colocalization. The glycine receptor formed by either alpha1 or alpha(3) shows rapid kinetics, whereas alpha(2) or alpha(4) receptors respond tonically. The use of transgenic mice has allowed the study of the different glycine receptor alpha subunits in the glycinegic neurotransmission of the mammalian retina. AIM: To describe the participation of the glycine receptor in the inhibitory neurotransmission particularly in the retina. DEVELOPMENT: In this review we describe the experiments that have allowed the localization and the involvement of the alpha subunit isoforms in specific transmission circuits of the vertebrate retina. CONCLUSIONS: The localization of the glycine receptor conformed by different isoforms of the alpha subunit in specific neuronal types, indicate the presence of glycinergic circuits that encode information differently in the retina.
Assuntos
Proteínas do Olho/fisiologia , Glicina/fisiologia , Potenciais Pós-Sinápticos Inibidores , Receptores de Glicina/fisiologia , Retina/fisiologia , Células Amácrinas/efeitos dos fármacos , Células Amácrinas/fisiologia , Animais , Cloretos/metabolismo , Potenciais Pós-Sinápticos Inibidores/efeitos dos fármacos , Potenciais Pós-Sinápticos Inibidores/fisiologia , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Isoformas de Proteínas/fisiologia , Subunidades Proteicas , Receptores de Glicina/efeitos dos fármacos , Células Bipolares da Retina/efeitos dos fármacos , Células Bipolares da Retina/fisiologia , Células Ganglionares da Retina/efeitos dos fármacos , Células Ganglionares da Retina/fisiologia , Estricnina/farmacologia , Transmissão Sináptica , Vertebrados/metabolismo , Vias Visuais/efeitos dos fármacos , Vias Visuais/fisiologiaRESUMO
Sensory experience is critical for the formation of neuronal circuits and it is well known that neuronal activity plays a crucial role in the formation and maintenance of synapses. In the vertebrate retina, exposure to different environmental conditions results in structural, physiological, neurochemical and pharmacological changes. Serotoninergic (5HT) amacrine cells of the chicken retina are bistratified interneurons whose primary dendrites descend through the inner nuclear layer (INL) to branch in the inner plexiform layer (IPL) forming two plexi, an outer network, localized to sublamina 1, and an inner network, localized to sublamina 4 and 5 of the IPL. Their development is temporally correlated with the establishment of synapses in the retina and with the emergence of the typical adult electroretinogram. It is unknown, however, which role these cells play in processing visual information and whether visual deprivation modifies their phenotype. Here, we show that, in the chicken, red-light rearing from hatching to postnatal day 12 significantly alters the stratification pattern of 5HT amacrine cells, inhibiting their age-dependent pruning measured with morphometric and densitometric procedures; as well as increasing serotonin immunoreactivity measured as relative optical density. This change in dendritic arborization, accompanied by an increase in serotonin concentration in dark adapted conditions, may decrease visual threshold, thus increasing visual sensitivity.