Journal
NEUROBIOLOGY OF LEARNING AND MEMORY
Volume 141, Issue -, Pages 108-123Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.nlm.2017.03.021
Keywords
Rat; Reuniens and rhomboid nuclei; Systems-level consolidation; Hippocampus; Enriched environment; Prefrontal cortex
Funding
- University of Strasbourg
- Centre National de la Recherche Scientifique (CNRS)
- Institut National de la Sante et de la Recherche Medicale (INSERM)
- ANR THALAME [ANR-14-CE13-0029-01]
- University of Damascus (Syria)
- French government
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Lesions of the reuniens and rhomboid (ReRh) thalamic nuclei in rats do not alter spatial learning but shorten the period of memory persistence (Loureiro et al. 2012). Such persistence requires a hippocampo-cortical (prefrontal) dialog leading to memory consolidation at the systems level. Evidence for reciprocal connections with the hippocampus and the medial prefrontal cortex (mPFC) makes the ReRh a potential hub for regulating hippocampo-cortical interactions. As environmental enrichment (EE) fosters recovery of declarative-like memory functions after diencephalic lesions (e.g., anterior thalamus), we studied the possibility of triggering recovery of systems-level consolidation in ReRh lesioned rats using a 40-day postsurgical EE. Remote memory was tested 25 days post acquisition in a Morris water maze. The functional activity associated with retrieval was quantified using c-Fos imaging in the dorsal hippocampus, mPFC, intralaminar thalamic nuclei, and amygdala. EE enhanced remote memory in ReRh rats. Conversely, ReRh rats housed in standard conditions were impaired. C-Fos immunohistochemistry showed a higher recruitment of the mPFC in enriched vs. standard rats with ReRh lesions during retrieval. ReRh rats raised in standard conditions showed weaker c-Fos expression than their sham-operated counterparts. The reinstatement of memory capacity implicated an EE-triggered modification of functional connectivity: EE reduced a marked lesion-induced increase in baseline c-Fos expression in the amygdala. Thus, enriched housing conditions counteracted the negative impact of ReRh lesions on spatial memory persistence. These effects could be the EE-triggered consequence of an enhanced neuronal activation in the mPFC, along with an attenuation of a lesion-induced hyperactivity in the amygdala. (C) 2017 Elsevier Inc. All rights reserved.
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