Temporal Coordination of Rac1 Signaling and Parvalbumin Interneurons in Hippocampal Pattern Separation Underlies Proactive Inhibition Control

Proactive inhibition (PI), where previously learned information interferes with new memory formation, represents a fundamental challenge in cognitive control, yet its neural mechanisms remain poorly understood. We investigated how hippocampal memory activity and parvalbumin-positive (PV) interneurons coordinate to regulate PI using modified novel object recognition paradigms with systematic manipulation of inter-stimulus intervals (ISI) and cognitive load (1-4x). Immunofluorescence analysis examined cFos, Rac1-GTP and PAK1 expression in hippocampal CA1 and dentate gyrus (DG) regions, while optogenetic manipulation targeted PV interneurons during memory consolidation. Our results revealed that both ISI and cognitive load conditions led to decreased hippocampal cFos expression and increased Rac1-GTP and PAK1 expression. Short ISI conditions (1-30min) produced significantly stronger PI effects than long ISI (1-4hr), accompanied by elevated Rac1-GTP and PAK1 expression in both CA1 and DG regions. High cognitive load similarly enhanced PI and increased hippocampal Rac1 and PAK1 activation. Critically, optogenetic activation of DG PV interneurons during short ISI periods rescued memory performance by reducing Rac1 and PAK1 expression in the DG region. Furthermore, activation of PV interneurons in DG enhanced memory performance while inhibition of PV interneurons impaired it, effects that were mediated through modulation of cFos expression in CA1. These findings reveal a temporally coordinated regulatory network where PV interneurons maintain pattern separation through rapid inhibitory control while suppressing interference-related molecular cascades, enabling the hippocampus to preserve memory precision under competing information conditions and providing potential therapeutic targets for memory-related cognitive disorders.