Modulation of horizontal cell function by dopaminergic ligands in mammalian retina.

Light responses of rabbit horizontal cell somata (HC) to flickering light stimuli recorded with sharp electrodes consist of a distinctive flicker component superimposed on a sustained hyperpolarisation. Activation of dopamine D1/D5 receptors depolarises HC dark membrane potential and suppresses the flicker component of responses to photopic stimuli without affecting the sustained hyperpolarising response component. Waveforms of responses to scotopic stimuli are preserved.

Dopaminergic modulation of horizontal-cell-axon-terminal receptive field size in the mammalian retina.

Receptive fields of gap junction-coupled axon terminals of B-type horizontal cells of isolated rabbit retinae were measured by recording light responses to slit shaped light stimuli at different eccentricities from the recording site. The D1/D5 agonist SKF-38393 and the membrane permeant second messenger 8-bromo-cAMP caused decreases of space constants by 20% while the D1/D5 antagonist SCH-23390 increased space constants by 25%. The results of this study indicate that axon terminal receptive fields of the rabbit retina can be modulated by D1/D5 receptor activation based on a cAMP-mediated mechanism.