Environmental conditions of recognition memory testing induce neurovascular changes in the hippocampus in a sex-specific manner in mice
Experiences are linked to emotions impacting memory consolidation and associated brain neuronal circuits. Posttraumatic stress disorder is an example of strong negative emotions affecting memory processes by flashbacks of past traumas. Stress-related memory deficits are also observed in major depressive disorder (MDD). We recently highlighted that sex-specific blood-brain barrier (BBB) alterations underlie stress responses in mice and human depression. However, little is known about the relationship between emotional valence, memory encoding and BBB function. Here, we investigated the effects of novel object recognition (NOR) test, an experience considered of neutral emotional valence, on BBB properties in dorsal vs ventral hippocampus in the context of various environmental conditions (arena size, handling, age). The hippocampus is a brain area central for learning and memory processes with the dorsal and ventral subregions being associated with working memory vs reference memory retrieval, respectively. Expression of genes related to BBB integrity are altered in line with learning and memory processes in a region- and sex-specific manner. We observed correlations between poor learning, anxiety, stress-induced corticosterone release and changes in BBB-associated gene expression. Comparison of BBB transcriptomes between sexes also revealed profound differences at baseline in both ventral and dorsal hippocampus. Finally, we identified circulating vascular biomarkers, such as sE-selectin and Mmp-9, altered following NOR exposure supporting that recognition memory formation has an impact on the neurovasculature. Although deemed as a neutral valence test, NOR experimental conditions impact performance, highlighting the need to minimize anxiety when performing this commonly used test in mice. Significance StatementWith this study, we aim to investigate the blood-brain barriers (BBB) role in memory acquisition and consolidation to unravel new mechanisms and decipher the involvement of non-neuronal cell types in these processes. For this purpose, male and female mice were subjected to a recognition memory test associated with a neutral emotional experience and impact on the transcriptomic profile of the BBB along with blood vascular biomarkers were evaluated under various experimental conditions. Crossing the BBB remains an important challenge to develop therapeutic drugs including in the context of memory deficits driven by psychiatric disorders or neurodegenerative diseases and thus, the possibility to directly target this barrier by better understanding its biology is attractive and innovating.