The role of D1-dependent dopaminergic mechanisms of the frontal cortex in delayed responding in rats.

The effects of local microinjections of D1-selective dopaminergic agents into the medial wall of the frontal cortex of rats on short-term memory processes were studied, along with the effects of proactive interference in immediate and delayed spatial choice tasks in a Y maze. Microinjections of the D1 receptor antagonist SCH23390 (1 nmol) disturbed performance of both immediate and delayed choice tasks. while administration of the D1 receptor agonist SKF38393 (1 nmol) had no effect on immediate choice and improved delayed performance. The effects of proactive interference, induced by microinjections of SCH23390 and SKF38393 into the frontal cortex, were significantly more marked in delayed choice than in the non-delayed task. Administration of SCH23390 increased the number of erroneous excursions made by the animals, the directions of these excursions coinciding with the preferred direction of rotation of the animals in a rotation test. The results obtained here lead to the conclusion that blockade of dopaminergic transmission in the mediofrontal cortex of rats worsens the performance of spatial choice in a Y maze by strengthening proactive interference processes and disinhibiting the mechanisms which intemally prepare the animals to respond to a defined spatial direction with behavioral acts.