Conditioned Arc expression in CA1 of the rat hippocampus supports long-term memory for temporal events

Abstract

The hippocampus is important for the acquisition, storage, and retrieval of memories. It has been largely examined for its role in spatial and contextual memory, but the mechanisms of encoding temporal cues are not well understood. The present work explores the expression of an immediate early gene which contributes to synaptic changes associated with long-term plasticity, Arc, as a temporally-specific marker of hippocampal memory to a time-of-day cue in a novel conditioning procedure in rats. We video-recorded locomotor activity and delivered a clock time-specific, multimodal alarm signal to cage-paired rats for 14 days, and quantified Arc mRNA expression at conditioned and unconditioned times. We predicted that neural activity associated with a temporally-conditioned response to a time-of-day cue would include expression of Arc genes in the hippocampus and interactions with circadian cycles of sleep-wake behaviour