Intra-medial prefrontal administration of SCH-23390 attenuates ERK phosphorylation and long-term memory for trace fear conditioning in rats.

The prefrontal cortex is known to be involved in the acquisition of trace conditioning, a higher-cognitive form of Pavlovian conditioning in which a conditioned stimulus and an unconditioned stimulus are separated by a time gap. We have recently reported that medial prefrontal (mPFC) extracellular-signal regulated kinase (Erk) phosphorylation is involved in the long-term memory storage of trace fear conditioning. Because of the important role dopamine D1 receptors play in prefrontal function, such as working memory, and due to evidence that dopamine D1 receptor activity can modulate plasticity, we investigated their role in prefrontal Erk phosphorylation following trace fear conditioning. We found that inhibition of dopamine D1 receptors through intra-mPFC infusion of SCH-23390 (1 microg/0.5 microL) 15 min prior to trace fear conditioning resulted in a decrease in training-related Erk phosphorylation. Additionally, pre-training intra-mPFC infusion of SCH-23390 also resulted in the impairment of long-term retention of CS-US association. These findings implicate mPFC dopamine D1 receptor activity in the storage of long-term memory for higher-cognitive associative tasks.