Light Responses From One Type On-Off Amacrine Cells in the Rabbit Retina.
Dacheux, Ramon F. and Elio Raviola.
Department of Neurobiology, Harvard Medical School, Boston, MA 02115.
APStracts 2:0228N, 1995.
SUMMARY AND CONCLUSIONS
1. The light responses from one type of on-off amacrine cells were recorded
intracellularly in the superfused rabbit retina under various conditions of
light adaptation. These recordings were obtained from cells located central
area, 5-7 mm inferior and directly below the optic nerve head. 2. On-off
amacrine cells responded to the initiation and termination of light stimuli
with transient depolarizations. Their receptive fields were about 0.8 to 1 mm
in diameter and did not exhibit antagonistic center-and-surround organization.
3. The cells received rod input since they responded to very dim scotopic
stimuli. With prolonged dark adaptation, the cells became more sensitive to
the initiation than termination of the stimulus, for the on-component of the
light response had a lower threshold than the off-component. 4. The cells
continued to respond to test flashes when the retina was adapted to a
background illumination of rod-saturating intensity. Thus, on-off amacrine
cells also receive cone input. Under these photopic conditions, a secondary
after-potential was observed following the off-component. Its characteristics
were different from those of the rod after-effect reported in other retinal
cells of the rabbit because its latency and amplitude changed with increasing
stimulus intensity. 5. Intracellular injections of horseradish peroxidase
showed that the recordings were obtained from a class of on-off amacrine cell
whose wide-field, unistratified dendrites were rigorously confined to the
middle of the inner plexiform layer or stratum 3. 6. The conspicuous rod and
cone inputs into a class of amacrine cells that are connected neither to rod
bipolars nor to AII amacrine cells, strongly support the idea that in the
rabbit the rod pathway uses cone bipolars as interneurons to distribute
scotopic signals to ganglion and cone-driven amacrine cells.
Received 16 March 1994; accepted in final form 27 July 1995.
APS Manuscript Number J135-4
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 14 August 1995.