Temporal order memory (TOM) enables organisms to discriminate the relative recency of events. Using a two-session training protocol in mice, we identified a window in which a second exploration session one hour after initial object presentation significantly impaired the stability of the first recognition memory.
Extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation was dynamically regulated during TOM formation, whereas total MKP3, its cognate phosphatase, increased under inhibitory conditions. In vivo pharmacological interventions using PD (MEK inhibitor) and BCI (MKP3 inhibitor) demonstrated that TOM stability depends on ERK1/2 signaling within the prefrontal cortex (PFC). Intra-PFC inhibition of ERK1/2 mimicked the behavioral interference effect, whereas MKP3 inhibition protected the initial memory trace.
To investigate the cellular and synaptic mechanisms underlying these findings, we performed whole-cell patch-clamp recordings from layer V pyramidal neurons in mouse PFC slices. Slices were pre-incubated with phosphorylation and dimerization modulators, previously shown to impair memory, to determine the effect of ERK1/2 activity regulation on intrinsic neuronal excitability and long-term potentiation (LTP).
By integrating behavioral phenotyping, molecular analyses, and electrophysiology, this multi-scale approach seeks to establish mechanistic links between ERK signaling, prefrontal synaptic plasticity, and the temporal organization of episodic memory.
