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S Vallerga

Publications and source records attributed to S Vallerga.

12 recordsLinked to original sources
PubMed1991

An interplexiform cell in the goldfish retina: light-evoked response pattern and intracellular staining with horseradish peroxidase.

The light-evoked response pattern and morphology of one interplexiform cell were studied in the goldfish retina by intracellular recording and staining. The membrane potential of the cell spontaneously oscillated in the dark. In response to a brief light stimulus, the membrane potential initially gave a slow transient depolarization. During maintained light, the oscillations showed a tendency to be suppressed; the response of the cell to the offset of the stimulus was not so prominent. The perikaryon of the interplexiform cell was positioned at the proximal boundary of the inner nuclear layer. The cell had two broad layers of dendrites; one was diffuse in the inner plexiform layer, the other was more sparse in the outer plexiform layer. The morphological and electrophysiological characteristics of the cell are discussed in relation to dopaminergic interplexiform cells and the light-evoked release pattern of dopamine in the teleost retina.

Animals↗
PubMed1991

Ganglion cells in the goldfish retina: correlation of light-evoked response and morphology.

Goldfish retinal ganglion cells were intracellularly stained with horseradish peroxidase after recording their responses to a predetermined set of test stimuli. Depolarizing responses were elicited by cells differing in shapes and sizes of their somata and dendritic fields; these cells were mostly bistratified in the inner plexiform layer (sublamina b and distal sublamina a). Hyperpolarizing responses were generated by cells monostratified in a, and by cells bistratified in a and at the a/b border. Responses that were hyperpolarizing to long wavelengths and involving large superimposed depolarizations for short wavelengths were recorded from cells with somata displaced in the inner nuclear layer. The latter cell group had wide, elliptical dendritic fields (confined to the distal sublamina a) and very fine axons. The ganglion cell types recorded are compared with morphological classification schemes proposed from earlier studies. Possible "structure-function" relations are also discussed.

Animals↗
PubMed1990

Variability of light-evoked response pattern and morphological characterization of amacrine cells in goldfish retina.

Amacrine cells of the goldfish retina were characterized electrophysiologically and subsequently labelled by intracellular injection of horseradish peroxidase. An attempt was made to broaden the electrophysiological classification of the cells. Light-evoked sustained amacrine cell responses were divided into two subtypes depending on colour opponency. Colour-coded responses (red/depolarizing and green/hyperpolarizing) were found to arise in amacrine cells possessing highly polarized dendritic fields; the dendrites were monostratified in the proximal half (sublamina b) of the inner plexiform layer. Non-colour-opponent sustained responses also arose in monostratified units, but the level of dendritic ramification was in sublamina a or b (hyperpolarizing or depolarizing units, respectively). Transient (ON-OFF) responses were associated mainly with bi- or multi-stratified or diffuse amacrine cells. Some variability was observed in the sizes of the dendritic fields in different sublaminae. There was a tendency for units with brisk components of responses to be narrowly stratified in the inner plexiform layer. Some units possessed "distant" dendrites. Several aspects of structure-function correlation in amacrine cells are discussed.

Animals↗
PubMed1989

Populations of retinal neurones marked with DAPI in lower vertebrates.

Retinae of teleosts, the marine sparid Boops boops and the fresh water cyprinid Carassius auratus, and amphibians, the anuran Rana pipiens and the urodele Ambystoma tigrinum, were stained in vitro with DAPI (4'6-diamidino 2-phenylindole). In all the preparations tested DAPI consistently stained nuclei in the ganglion cell layer, and three levels of nuclei could be observed from IPL (inner plexiform layer) to INL (inner nuclear layer) in the bogue, goldfish and frog retinae. In the goldfish retina a dense mosaic of stained horizontal cell nuclei was also observed. Both single and double cones were stained in fish; no photoreceptor staining could be found in amphibian retinae. Goldfish and frog retinae were incubated with 5'7'-DHT (dihydroxytryptamine) to compare the distribution of DAPI-stained cells with that of putative serotoninergic neurones. Fluorescent cells were found in the ganglion cell layer, and at two levels distally. In fixed retinae only a regular array of cells was found in the proximal INL, and interestingly the cell density equalled the density of serotoninergic amacrine cells. No other fluorescing cells could be detected. In the fixed frog retina two populations of fluorescent cells were found in the INL. For both species tested 5'7'-DHT and DAPI fluorescent populations did not overlap. The images of fluorescent cells were then processed, in order to improve image quality and assess if, in living tissue, cell types could be separated according to differences in intensity of fluorescence. It emerged that the size of fluorescent nuclei is inversely proportional to their optical density.

Amphibians↗
PubMed1986

Relation between light responses and dendritic branching in the salamander ganglion cells.

Ganglion cells in larval tiger salamander retina were differentiated into different types according to their light response and morphology. Sustained hyperpolarizing responses were recorded from ganglion cells branching in the sclerad half of the inner plexiform layer (IPL). Sustained depolarizing responses were elicited in cells with dendrites confined in the vitread portion of the IPL. Transient responses were associated with two types of morphological units sharing level of branching, in the middle of the IPL, but differing for soma location (inner plexiform or inner nuclear layer).

Animals↗
PubMed1984

Differentiation, extent and layering of amacrine cell dendrites in the retina of a sparid fish.

The morphology of amacrine cells has been studied in Golgi-stained retinae of the salt water sparid Boops boops. The great variety of size and shapes of amacrine cells has been organized into five classes according to the qualitative parameter 'dendritic architecture', which describes the number, size, course, degree of dichotomy, and varicosity of dendrites. Extent of dendritic field and depth of stratification in the inner plexiform layer, viewed as quantitative variations of a given cell type morphology, complete the criteria for classification. Each amacrine cell is unequivocally defined by a three element code according to the values assumed by the parameters used for the classification. The possible functional implications of dendritic morphology are briefly discussed.

Animals↗
PubMed1980

Rod and cone signals in the horizontal cells of the tiger salamander retina.

1. Intracellular recordings of horizontal cell responses to monochromatic lights of various wave-lengths and intensities were made in the retina of the larval tiger salamander in order to determine the contributions of rod and cone activities to horizontal cell responses. 2. Under conditions of extensive dark adaptation, and with dim light stimulation, the horizontal cell responses reflected mainly rod activity. In the light-adapted state or at high light intensities the cone contribution was dominant. 3. Bright adapting flashes selectively suppressed the rod component of horizontal cell responses. 4. Intracellular recordings from rods and cones showed that interactions between the two receptor types are very small and cannot account for the large rod--cone mixed input observed in horizontal cells. It is concluded that this input is mediated by direct connexions between receptors and horizontal cells.

Adaptation, Ocular↗
PubMed1975

Horizontal cell responses in the retina of the larval tiger salamander.

The responses to light of horizontal cells were recorded intracellularly in the retina of the larval tiger salamander. 2. All the units studied had a large summation area and were hyperpolarized by circles of light of any wave-length centred on the recording electrode, but two types could be distinguished according to the properties of their receptive fields. Type A units were hyperpolarized following illumination of any portion of their receptive field, while type B units were not hyperpolarized by illumination of their surround unless the centre was simultaneously illuminated, stimulation of the surround alone resulting in either a small depolarization or virtually no response. 3. Procion yellow injections showed that type A responses are recorded from thick and long processes not directly continuous with an identifiable cell body, while type B responses originate from the cell body of cells that send very fine and tortuous processes towards the receptors. The histological observations also suggested that the type A units represent expansions or swellings of one or more of the fine processes originating from the type B units. Therefore, it seems possible that both types of units are just different parts of a single kind of horizontal cell, and that a majority of the dye injections failed to stain them simultaneously because of the small diameter of the connecting process. 4. The large summation area of type A units can be explained, just as for horizontal cells in other retinae, by supposing that they are electrically coupled to other units of the same type. The receptive field properties of type B units, however, can only be partly explained by electrical coupling, and then only if the existence of voltage-dependent junctions is postulated. Instead, the reversal of the polarity of responses to an annulus of light during steady illumination of the centre, plus the available electron microscopic evidence, suggest that the effect of the surround on the type B units is due to a chemical synaptic impingement from the type A units.

Ambystoma↗