We studied the light-evoked responses of AII amacrine cells in the @entity95 retina under dark- and light-adapted conditions. In contrast to the results of previous studies, we found that AII cells display robust responses to light over a 6-7 log unit intensity range, well beyond the operating range of rod photoreceptors. Under dark adaptation, AII cells showed an ON-center/OFF-surround receptive-field organization. The intensity-response profile of the center-mediated response component followed a dual-limbed sigmoidal function indicating a transition from rod to cone mediation as stimulus intensities were increased. Following light adaptation, the receptive-field organization of AII cells changed dramatically. Light-adapted AII cells showed both ON- and OFF-responses to stimulation of the center receptive field, but we found no evidence for an antagonistic surround. Interestingly, the OFF-center response appeared first following rapid light adaptation and was then replaced gradually over a 1-4 min period by the emerging ON-center response component. Application of the metabotropic @entity2227 receptor agonist APB, the ionotropic @entity2227 blocker CNQX, @entity8263 , and the @entity842 donor SNAP all showed differential effects on the various center-mediated responses displayed by dark- and light-adapted AII cells. Taken together, these pharmacological results indicated that different synaptic circuits are responsible for the generation of the different AII cell responses. Specifically, the rod-driven ON-center responses are apparently derived from rod bipolar cell synaptic inputs, whereas the cone-driven ON-center responses arise from signals crossing the gap junctions between AII cells and ON-center cone bipolar cells. Additionally, the OFF-center response of light-adapted AII cells reflects direct synaptic inputs from OFF-center cone bipolar cells to AII dendritic processes in the distal inner plexiform layer.

Comparison of the responses of AII amacrine cells in the dark- and light-adapted XXXX retina.

@entity8263 :: ('MESH:C016276', 'Chemical') :: ['8-bromo-cGMP'] @entity2227 :: ('CHEBI:29987', 'Chemical') :: ['glutamate'] @entity95 :: ('9986', 'Species') :: ['rabbit'] @entity842 :: ('MESH:D009569', 'Chemical') :: ['nitric oxide']
@entity95 :: (9986,Species) :: ['rabbit']
