Glucocorticoid-induced enhancement of contextual fear memory consolidation in rats: Involvement of D1 receptor activity of hippocampal area CA1

• D1 rather than D2 receptor is involved in CORT-induced enhancement of fear memory consolidation.
• Neither D1 nor D2 antagonism in area CA1 affected total locomotor activity.
• CORT treatment may reduce D1 rather than D2 receptor mRNA expression of hippocampal CA1.

This study investigated the role of dopamine (DA) receptors in area CA1 of the hippocampus in modulating the effects of glucocorticoids on the contextual fear memory consolidation. Adult male rats were given systemic injections of corticosterone (CORT; 3 mg/kg) immediately after training in a contextual fear conditioning (CFC) task and the percentage of time spent freezing in the CFC context was recorded 24 h after training. Intra-CA1 infusion of the DA type 1 (D1) receptor antagonist SCH 23390 (SCH; 30 ng/0.5 µl per side) immediately after CORT injection attenuated CORT-induced enhancement of memory consolidation. However, intra-CA1 infusion of the DA type 2 (D2) receptor antagonist sulpiride (SUL; 60 ng/0.5 µl per side) was ineffective. Neither antagonist alone altered freezing behavior in the 24 h CFC retention test. Furthermore, the memory enhancing dose of CORT used in these experiments reduced D1, but not D2, receptor mRNA expression in area CA1. Neither D1 nor D2 antagonism in area CA1 affected total locomotor activity. These findings provide evidence for the involvement of hippocampal D1 receptor activity in area CA1 in CORT-induced enhancement of contextual fear memory consolidation.