Dopaminergic deficiency causes delayed visual evoked potentials in rats.

Flash and pattern visual evoked potentials (VEPs) to two temporal frequencies of stimulation were studied in nineteen rats. The effect of a tyrosine hydroxylase inhibitor and of a dopamine receptor blocker on the VEP was explored in ten animals. Significant latency change occurred following injection of either drug, while only the hydroxylase inhibitor reduced the VEP amplitude. These changes were not caused by the anesthesia used in these experiments, although the same anesthetics in higher doses did depress VEP amplitudes. When dopamine blockade was followed by administration of apomorphine, a dopamine agonist, VEP delays could be partially reversed. Besides conduction defects of myelinated axons, synaptic malfunction may also cause delays in sensory evoked potentials.