Does Intravitreal Dopamine Agonist and Antagonist Administration Have Effects on the Brain? An Experimental Study in Rats

Objective: There might be dopaminergic connections between the retina and the brain. In this context, the study was aimed to investigate the possible interaction between the retina and basal ganglia through the dopaminergic system. Materials and Methods: In total, 32 healthy rats were randomized into 4 groups: healthy, Sham, dopamine antagonist injected group (risperidone, 0.04 mg/kg intravitreally), and dopamine agonist injected group (apomorphine, 0.4 mg/kg intravitreally). The locomotor activity and Morris water maze tests were applied to all rats twice, before the injection and 28 days after, to detect changes in movement, memory, and attention. Histopathologically, the basal ganglia and hippocampus regions were removed and examined. Results: In the locomotor activity test, a statistical significance was found between the first and last measurement values of the apomorphine group and a decrease in activities and an increase in resting times (P < .05). In the Morris water maze test, a statistical significance was detected between the first and last tests of the control group and the apomorphine groups and showed significantly shorter learning times (P < .05). Histological analyses of the substantia nigra and hippocampus were noteworthy in that the number of damaged neurons in the risperidone group was considerably higher than the other groups. The number of damaged neurons in the apomorphine group was significantly lower than in the healthy group. Conclusion: Intravitreal administration of dopamine agonists and antagonists has given rise to alterations in the cerebral dopaminergic system, leading to changes in locomotor activity and memory and histopathological changes.