Electrophysiological study of retinal rod-cone interaction

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The purpose of the present study is to elucidate the functional significance of dopamine (DA) in the retina. We studied effects of dopamine and a potent D_1-D_2 blocker, haloperidol, on retinal function in the albino rabbit in vivo. An intravitreal injection of dopamine suppressed the scotopic b-wave and enhanced the oscillatory potentials (OPs) elictited by repeated bright flashes, but did not significantly affect the photopic b-wave. An intravitreal injection of haloperidol suppressed the photopic b-wave and the OPs. An additional intravitreal injection of dopamine to the haloperidol-injected eyes resuscitated the OPs over the pre-haloperidol status. These results suggest that dopamine mediates the light-adaptive processes of the scotopic system, eventually facilitating the photopic system function via disengagement of rod-cone inhibition. Enhancement of the OPs by intravitreal DA injection was blocked by a simultaneous intravitreal injection of SCH 23390 (D_1 antagonist) but not by that of sulpiride (D_2 antagonist) (50muM,100muM). These results suggest that D_1 receptor is mainly responsible for the DA-induced enhancement of the OPs. Nomifensine (NF), a potent DA-uptake blocker, enhanced the amplitude of the OPs. NF attenuated the amplitude of the scotopic b-wave, leaving the peak latency of the scotopic b-wave unaltered. Neither the dark-adapted a- nor b-waves was altered at any NF concentration tested. 1muM DA and 30muM NF together, each of which is insufficient to alter either of the scotopic b-wave or the OPs when applied solely, reduced the scotopic b-wave and enhanced the OPs. These results suggest that the intrinsic DA release in the retina is large enough to alter the ERG.