Effects of D-1 and D-2 dopamine antagonists on ERG and optic nerve response of the cat

Various concentrations of three dopamine antagonists (fluphenazine, haloperidol and sulpiride) with different affinities to the receptor subtypes were applied in order to test their effect on responses from outer (isolated PIII-component of the ERG), middle (b-wave) and inner (optic nerve response, ONR) retinal layers, recorded from dark-adapted, isolated, arterially-perfused cat eyes. In the range of concentrations tested (e.g. from 4 nmol ml-1 to 16 mumols ml-1 for haloperidol) none of the drugs added to the perfusion medium had any effect on either slow or fast PIII-amplitude or on the temporal characteristics of the response. All dopamine antagonists increased the rod b-wave with a comparable molar efficacy. The rod b-wave latency and implicit time showed no drug-induced changes. In the rod ONR the D-1 antagonist fluphenazine increased the fast transient on-component while it simultaneously strongly decreased the off-component. IN contrast, concentrations of the D-2 antagonists sulpiride that had a comparable effect on the ONRs fast transient on-component influenced neither the slow transient on-component nor the off-component. These findings indicate that the D-1 and D-1 receptors play different roles in the transmission of rod signals at the border of middle and inner retina.