Proactive Interference Unmasks Sex-Divergent Recognition Memory Instability and Catecholaminergic Dysfunction in Early-Stage Alzheimer’s model

Background Proactive interference (PI) is a major contributor to early memory decline in Alzheimer’s disease (AD), yet its mechanistic basis and sex specificity remain poorly understood. Novel object recognition (NOR) memory is typically preserved in 2-month-old APP/PS1 mice, representing a presymptomatic stage. We investigated whether PI destabilizes recognition memory at this early stage and whether sex-specific differences in hippocampal engram recruitment and catecholaminergic regulation underlie vulnerability or resilience. Methods Male and female APP/PS1 and wild-type (WT) mice underwent 3 days of contextual habituation followed by a 1-h PI session, and NOR acquisition 24 h later. Memory was tested after 24 h using novel/familiar object discrimination, scored manually by blinded investigators. c-Fos immunohistochemistry quantified dorsal CA3 (dCA3) engram reactivation 90 min post-test. Tyrosine hydroxylase (TH) immunostaining measured dopaminergic axon density in CA3, CA1, and DG; silver staining excluded neurodegeneration. Norepinephrine (NE) levels were assessed by ultra-high-performance liquid chromatography (uHPLC), and norepinephrine transporter (NET) protein levels post-NOR/PI + NOR. Behavioral data were analyzed by two-way ANOVA with Tukey’s post-hoc tests, and immunohistochemical data by unpaired t-tests or ANOVA as appropriate. Results NOR memory was intact in all groups under baseline conditions. PI selectively impaired recognition in male APP/PS1 mice but spared females and WT controls. Male WT mice showed increased dCA3 c-Fos activation under PI, whereas APP/PS1 males failed to recruit additional ensembles, dissociating behavior from neuronal activation. Females exhibited lower overall c-Fos activation but preserved recognition memory, indicating circuit-level resilience. TH + axon density was selectively reduced in male APP/PS1 mice across CA3, CA1, and DG, with silver staining confirming absence of overt degeneration. NE levels showed a non-significant upward trend in males, while baseline NET expression was unchanged but downregulated after NOR and PI + NOR in both sexes. Conclusions PI serves as a sensitive probe of early recognition instability in AD. Male APP/PS1 mice exhibit impaired CA3 recruitment and dopaminergic terminal loss, leading to memory destabilization despite noradrenergic modulation. Females preserve recognition through compensatory mechanisms. These findings reveal sex-divergent catecholaminergic regulation as a critical determinant of early cognitive vulnerability and highlight interference-based paradigms as translational markers for prodromal AD.