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P L Marchiafava

Publications and source records attributed to P L Marchiafava.

At least 19 recordsLinked to original sources
PubMed1989

Membrane resistance properties of pineal photoreceptors in the trout.

Intracellular recordings were obtained from pineal photoreceptors of the trout Salmo irideus. Illumination produced graded hyperpolarizing responses whose time course resembled that of retinal cones in lower vertebrates. Current-voltage relations were derived by using a voltage-clamp technique in the dark and during illumination. Membrane resistance values obtained in the dark were about 550 M omega, and they increased during illumination. The extrapolated reversal potential of the photocurrent is about 55 mV above the dark membrane potential, indicating that an ionic mechanism similar to that in retinal photoreceptors may be involved.

Animals↗
PubMed1986

Subsurface cisternae in retinal double cones.

Double cones of tench and goldfish retina are characterized by extensive subsurface cisternae underlying the plasma membranes at the appositional area between the principal and accessory cone. Such a membrane system is absent in double cones of turtle and salamander retina. Measurements on both transverse and longitudinal sections gave a total appositional area of about 75 square microns, the subsurface cisterna in each element of the double cone being around 8-10% smaller due to multiple fenestrations at the level of the paraboloid. No gap junctions joining the inner segments of tench and goldfish double cones were detected, while gap junctions could be observed at the level of the ellipsoid and paraboloid of turtle double cones. The possible role of the subsurface cisternae in functional interactions between double cone elements is discussed.

Animals↗
PubMed1985

Intracellular recording from single and double cone cells isolated from the fish retina (Tinca tinca).

Intracellular recording were obtained from isolated single and double cone cells of the tench retina. Photoresponses show features characteristic of other species and behave linearly with very dim illumination. The cells spectral sensitivity matches their pigment absorption spectrum measured by previous authors. The principal and accessory members of double cones show a maximal sensitivity peak at about 644 and 547 nm, respectively. In addition, each of the two action spectra shows a secondary inflection at the peak wavelength of the adjacent member, suggesting functional coupling between the two members of double cones.

Animals↗
PubMed1983

An "antagonistic" surround facilitates central responses by retinal ganglion cells.

Ganglion cells in the turtle retina respond to increments of saturating illumination of the receptive field centre by progressively decreasing the number of spikes of the responses, perhaps as a result of membrane inactivation. Intracellular recording indicates that a simultaneous illumination of the receptive field surround greatly facilitates the "suprasaturated" central responses, while the expected centre-surround antagonism is still present between photoresponses below saturation. It is suggested that both pre- and post-synaptic mechanisms provide the ganglion cells with the unique possibility, among other retinal cells, to shift their full dynamic range across more than 3 log units of illumination intensity.

Action Potentials↗
PubMed1982

The photoresponses of structurally identified amacrine cells in the turtle retina.

Intracellular recordings were obtained from amacrine cells afterwards identified morphologically by horseradish peroxidase injection. There is a correlation between the time course of the photoresponses and the distribution of the cell processes across the inner plexiform layer (i.p.l.). Cells producing the shortest duration, transient 'on-off' photoresponses branched in a single, narrow stratum of the i.p.l. (3-7 microns across). Transient photoresponses with a longer time course were recorded from cells branching in a thicker stratum of i.p.l. (up to 20 microns), or from bistratified cells. Amacrine cells producing sustained centre-on or centre-off photoresponses were radially diffused across the whole i.p.l.; therefore this type of photoresponse need not be associated with a specific cellular stratification within the i.p.l. It is concluded that the two main functional types of amacrine cell, i.e. transient on-off and sustained centre-on and centre-off, are subject to different structural organization of inputs than are the homologous physiological types of ganglion cells in this species, in the cat and in the carp. In a summary diagram the observed characteristics of the photoresponses are tentatively explained in terms of a non-homogeneous distribution of bipolar synaptic inputs along amacrine cell processes.

Animals↗
PubMed1981

Interactions leading to colour opponency in ganglion cells of the turtle retina.

In the turtle retina, colour-dependent photoresponses could be recorded intracellularly from ganglion cells receiving only bipolar cell input. Thus, the mechanism for colour discrimination by these ganglion cells (type A) is contained in the outer plexiform layer of the retina and depends on interaction between horizontal and cone cells. Ganglion cells receiving an additional amacrine input (type B) are not influenced by colour, and have about 0.7 logarithmic unit lower absolute sensitivity to peak wavelength than have type A ganglion cells.

Animals↗
PubMed1980

Intracellular analysis and structural correlates of the organization of inputs to ganglion cells in the retina of the turtle.

Intracellular recording from the ganglion cells of the retina of the turtle Pseudemys scripta elegans shows that the photoresponses are characterized by either of two reversal potentials. These have been related to the bipolar and amacrine cell inputs to ganglion cells. Of the recorded ganglion cells, 33% (type A) are driven predominantly by one type of input, attributed to bipolar cells. Other ganglion cells (66%, type B) receive a mixed input from bipolar and amacrine cells. Type A ganglion cells show a higher conduction velocity (up to 3 m/s) and a higher firing frequency (up to 160 spikes per second) than type B cells. By injecting Procion yellow into bipolar, amacrine and ganglion cells it may be observed that type A ganglion cells ramify only in those regions of the inner plexiform layer that contain cell processes originating exclusively from the bipolar cell type predicted from the recordings. Type B ganglion cells ramify throughout the inner plexiform layer in either a multi-stratified or a diffuse fashion.

Action Potentials↗
PubMed1978

The responses of amacrine cells to light and intracellularly applied currents.

1. Intracellular responses to light were recorded from amacrine cells in the retina of the turtle Pseudemys scripta elegans. 2. The recorded responses were identified on the basis of physiological criteria reported previously (Marchiafava, 1976). Amacrine cells produced transient 'on' and 'off' depolarizing responses irrespective of the retinal area illuminated and of wavelength. 3. The transient depolarizing responses increased by enlarging the illuminated circle up to 120 micrometer in radius. Circles covering larger areas, up to 200 micrometer, produced a relative decrease of the response amplitude. Thus, amacrine cells' receptive fields appear as a central 'excitatory' area of about 120 micrometer radius, surrounded by a 'suppressor' area. 4. Amacrine cells' photoresponses were associated with an increase in membrane conductance. The responses to illumination of central or peripheral areas of the receptive field, however, showed different reversal potentials. The responses to peripheral illumination reversed at about 15 mV above resting potential, while the equilibrium potential of the centre-photoresponses was indicated by extrapolation at about +30 mV. No conductance chance was detectable during steady lights. 5. Repetitive stimulation of the optic nerve invariably reduced amacrine cells' photoresponses, but not those recorded from bipolar cells. It follows then that only ganglion cell photoresponses originating from amacrines' input would be depressed by the nerve stimulation, which thus becomes a reliable test to discriminate whether ganglion cell photoresponses originate from amacrine or bipolar inputs.

Action Potentials↗
PubMed1977

Self-facilitation of ganglion cells in the retina of the turtle.

1. Ganglion cells responses to illumination and to optic nerve stimulation were recorded intracellularly from the retina of the turtle. All ganglion cells were identified by their antidromic responses to optic nerve stimulation.2. When solitary spikes are produced following antidromic, orthodromic or intracellular stimulation, about 20% of the recorded ganglion cells show an additional depolarization along the falling phase of the action potential (post-spike depolarization, PSD).3. The PSD following the antidromic action potential disappears upon collision with a direct spike or when the antidromic spike is prevented from invading the cell soma.4. By pairing two optic nerve stimuli the PSD is depressed with brief interstimulus intervals, but gradually recovers to the control amplitude 600-800 msec after the conditioning shock.5. The PSD is tentatively interpreted as an e.p.s.p. transmitted by ganglion cell collaterals originating at the level of the soma dendritic complex of the recorded cell.6. The interspike interval histogram of ganglion cells showing PSD is characterized by a peak at about 10 msec, as opposed to a peak between 12 and 100 msec observed in cells without PSD. It is suggested that the occurrence of PSD facilitate the onset of additional action potentials at brief interspikes intervals, thus potentiating ganglion cell discharges.

Action Potentials↗
PubMed1976

Centrifugal actions on amacrine and ganglion cells in the retina of the turtle.

1. An electrophysiological investigation of efferent synapses in the retina of the turtle was conducted by recording intracellularly from amacrine cells. These cells have been selected because in birds they have been shown to have direct anatomical connexions with centrifugal fibre terminals. 2. Amacrine cells could be easily distinguished from most other retinal cells, except ganglion cells, by their different photo-responses. Because both amacrine and ganglion cells may generate action potentials they were distinguished by their responses to optic nerve stimulation. 3. The response of ganglion cells to single shock stimulation of the optic nerve consists of an antidromic action potential followed by a late synaptic potential. 4. Cells which did not show antidromic responses but were electrically excitable, by passing direct current through the recording electrode, were considered to be amacrine cells. 5. Amacrine cells generate an e.p.s.p. in response to optic nerve stimulation. An analysis of the e.p.s.p. suggests that it may be due to a single afferent fibre terminating in the proximity of the cell soma. By analogy to the bird, it is concluded that the amacrine cells e.p.s.p.s result from the activation of centrifugal fibres.

Action Potentials↗
PubMed1974

Light-induced resistance changes in retinal rods and cones of the tiger salamander.

1. The electrical properties of retinal rods and cones of the larval tiger salamander were investigated with intracellular electrodes, and the cells identified by means of dye injections.2. Both types of photoreceptors are hyperpolarized by illumination. Following stimulation with brief flashes of dim light, rod responses show a slower time course than cone responses; with bright flashes, rod responses can be recognized because of their long recovery time.3. Values of input resistance were derived from the voltage displacement induced by constant current pulses in darkness or at the peak of the photoresponse. The input resistance following illumination was also calculated from the effect of steady polarizing currents on the amplitude of the photoresponse.4. In darkness, the input resistance of the rod cells is time- and voltage-dependent, but the voltage-current relations of most cells have a linear region which includes the physiological limits of membrane potential. At the peak of the photoresponse, the input resistance (slope of the linear region of the v-i relations) is decreased.5. Cone cells show approximately linear v-i relations. As reported by previous authors, illumination increases the input resistance.6. These results support the current view that the cone photoresponse is the consequence of a reduction in the permeability of channels which in darkness shunt the membrane. In rods, however, it appears that the main effect of illumination is to increase the permeability of the membrane to ions for which the equilibrium potential is more negative than the membrane potential in darkness.

Animals↗