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J S Charlton

Publications and source records attributed to J S Charlton.

13 recordsLinked to original sources
PubMed1985

The arterially perfused eyecup of the tree squirrel, Sciurus carolinensis: a preparation for intracellular recording from mammalian retinal neurons.

The arterially perfused eyecup of the Eastern gray squirrel, Sciurus carolinensis, has been developed for the study of mammalian retinal neurons by the technique of intracellular recording. Particular emphasis is placed in this report on the development of a convenient perfusion chamber. The choice of this animal and the reason for choosing the arterially perfused open eyecup are also discussed. Intracellular recordings were made from all major types of neurons in the squirrel retina. Data are presented here from ganglion cells and bipolar cells.

Animals↗
PubMed1985

Response properties of horizontal cells and photoreceptor cells in the retina of the tree squirrel, Sciurus carolinensis.

A new experimental preparation for intracellular recording from mammalian retinal neurons has been established. This is the arterially perfused eyecup preparation of the tree squirrel, Sciurus carolinensis. Two horizontal cell types have been recorded in this preparation. These cell types differ in their response waveforms. Type 1 horizontal cells appear to receive input only from cones, whereas type 2 horizontal cells receive mixed rod-cone input. Sciurus horizontal cells have receptive-field sizes smaller than those of horizontal cells in other mammalian and nonmammalian species. Recordings from a second class of cells in the outer retina of the squirrel reveal receptive-field properties considerably different from those of squirrel horizontal cells and similar to those of photoreceptor cells in other species. On the basis of these receptive-field properties, recording depth, and spectral response characteristics, we conclude that these recordings were from cone-photoreceptor cells. These recordings from squirrel cones are the first demonstration of mammalian photoreceptor response amplitudes and receptive-field interactions comparable with those demonstrated for nonmammalian species.

Animals↗
PubMed1978

A quantitative comparison of the time-course of sensitivity changes produced by calcium injection and light adaptation in Limulus ventral photoreceptors.

The time-course of light and dark adaptation was quantitatively compared with the time-course of the onset of and recovery from desensitization produced by intracellular calcium injection in Limulus ventral photoreceptors. The onset of light adaptation tended to be faster (by 60-90 s) than the onset of desensitization produced by intracellular Ca++ injection. The initial portion of the time-course of dark adaptation was faster (about 10-20 s) than the time-course of recovery from desensitization produced by intracellular Ca++ injection. The final portion of recovery from Ca++ injection had the same time-course as a comparable dark adaptation.

Animals↗
PubMed1977

Enhancement and phototransduction in the ventral eye of limulus.

Limulus ventral photoreceptors were voltage clamped to the resting (dark) potential and stimulated by a 20-ms test flash and a 1-s conditioning flash. At a constant level of adaptation, we measured the response to the test flash given in the dark (control) and the incremental response produced when the test flash occurred within the duration of the conditioning flash. The incremental response is defined as the response to the conditioning and test flashes minus the response to the conditioning flash given alone. When the test flash was presented within 100 ms after the onset of the conditioning flash we observed that: (a) for dim conditioning flashes the incremental response equaled the control response; (b) for intermediate intensity conditioning flashes the incremental response was greater than the control response (we refer to this as enhancement); (c) for high intensity conditioning flashes the incremental response nearly equaled the control response. Using 10-mum diam spots of illumnination, we stimulated two spatially separate regions of one photoreceptor. When the test flash and the conditioning flash were presented to the same region, enhancement was present; but when the flashes were applied to separate regions, enhancement was nearly absent. This result indicates that enhancement is localized to the region of illumination. We discuss mechanisms that may account for enhancement.

Action Potentials↗
PubMed1977

A quantitative comparison of the effects of intracellular calcium injection and light adaptation on the photoresponse of Limulus ventral photoreceptors.

Calcium ions were iontophoretically injected into ventral photoreceptors of Limulus by passing current between two intracellular pipettes. Changes in sensitivity and photoresponse time course were measured for both light adaptation and Ca++ injection. We found for some photoreceptors that there was no significant difference in the photoresponse time course for desensitization produced by light adaptation or by Ca++ injection. In other photoreceptors, the time delay of photoresponse for Ca++ injection was slightly longer than for light adaptation. The variability of threshold response amplitude and time delay decreases when the photoreceptor is desensitized by either light adaptation or Ca++ injection. The peak amplitude versus log stimulus intensity relationships for controls, light adaptation, and Ca++ injection all could be described very closely by a single template curve shifted along the log intensity axis. A 40- to 50-fold change in sensitivity is associated with a 2-fold change in photoresponse time delay for both light adaptation and Ca++ injection.

Adaptation, Ocular↗
PubMed1977

Increased intracellular sodium mimics some but not all aspects of photoreceptor adaptation in the ventral eye of Limulus.

The effects of the intracellular iontophoretic injection of Na+ ions have been quantitatively compared with adaptation in ventral photoreceptors of Limulus. We find that: (a) both light adaptation and sodium injection are associated with a decrease in the variability of the threshold response amplitued; (b) both light adaptation and sodium injection are associated with a decrease in the absolute value of the temporal dispersion of the threshold response time delay; (c) the same template curve adequately fits the intensity response relationships measured under light adaptation and Na+ injection; (d) both light adaptation and Na+ injection produce a fourfold decrease in response time delay for a desensitization of 3 log units; (e) the time coures of light adaptation and dark adaptation is significantly faster than the onset of and recovery from desensitization produced by Na+ injection; (f) unlike local illumination, Na+ injection does not produce localized desensitization of the photoreceptor. These findings suggest that a rise in intracellular Na+ concentration makes at most only a minor contribution (probably less than 5%) to the total adaptation of these receptors in the intensity range we have examined (up to 3 log units above absolute threshold). However, changes in intracellular Na+ concentration may contribute to certain components of light and dark adaptation in these receptors.

Action Potentials↗
PubMed1975

Local adaptation in the ventral photoreceptors of Limulus.

Local adaptation was demonstrated in the ventral photoreceptors of Lumulus using either flashes or continuous illumination. Spots of light locally desensitized the region of the photoreceptor on which they were focused. In dark-adapted photoreceptors where "quantum bumps" were clearly discernible, local adaptation of the quantum bumps was observed. Local adaptation could induce differences of threshold of 1 decade over distances of 50-80 mum. With continuous local illumination these gradients could be maintained from 2 s to 30 min. In addition, the decrease in time scale associated with light adaptation was also found to be localized to the region of illumination.

Adaptation, Ocular↗