THE RETINAL DOPAMINE NETWORK ALTERS THE ADAPTATIONAL PROPERTIES OF RETINAL GANGLION-CELLS IN THE CAT

1. Single-unit extracellular recordings of optic tract fibers were use d to study ganglion cell (GC) response properties of the intact cat ey e before and after the intravitreal injection of haloperidol or SCH233 90, dopamine-specific antagonists. Nearly all of the dopaminergic cell s in the cat retina are amacrine cells (ACs); thus the dopamine antago nists are thought to primarily block the postsynaptic effects of these dopaminergic amacrine cells. All GCs encountered were subjected to a battery of receptive-field (RF) tests, including classification as X o r Y, and as ON or OFF. 2. The effects of haloperidol were greatest in the light-adapted OFF-center pathways and especially in the OFF-center Y-cell. Within 30 min of haloperidol injection, both the spontaneous and light-evoked activity of the OFF-center Y-cell fell to zero, but w hen the same cell was exposed to lower levels of steady-state backgrou nd illumination (scotopic levels), the response of the cell once again became robust. 3. OFF-Center Y-cells that had partially recovered fro m the drug effects and OFF-center X-cells recorded when the drug effec t was maximal both possessed intensity-response curves that were shift ed to the right of normal. 4. Recovery from the drug effects reflect s upranormal responses after the initial response reductions and may be due to haloperidol's action on the dopamine autoreceptor. 5. Of the ON -center cells, only the Y-cells showed response alterations; possessin g higher spontaneous activities and slightly reduced amplitudes to RF center (RFC) illumination. 6. The effects of SCH23390 paralleled those of haloperidol except that the onset was faster and the duration of t he action of SCH23390 was much shorter, and no supranormal responses f ollowed the initial effects. 7. Dark-adaptation functions of OFF-cente r GCs revealed a normal rod-cone shift; however, SCH23390 eliminated t he rod-cone break, and threshold quickly fell to that of the rod mecha nism. 8. The dopaminergic neurons of the cat retina appear to play an important role in regulating the activity of retinal OFF-center pathwa ys in the photopically adapted eye, and one of its functions may be to control the relative contributions of the rod and cone systems to the response properties of light-adapted OFF-center GCs. 9. It is argued that dopamine is released in the light and enhances cone pathway activ ity, perhaps in the outer retina at bipolar and horizontal cells, and suppresses rod pathway activity, perhaps in the inner retina at amacri ne cells.