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Klur, S. et al. Hippocampal-dependent spatial memory functions might be lateralized in rats: an approach combining gene expression profiling and reversible inactivation. Hippocampus 19, 800-816

RCMG, F. Hoffmann-La Roche Limited, CH 4070 Basel, Switzerland.
Hippocampus (Impact Factor: 4.3). 09/2009; 19(9):800-16. DOI: 10.1002/hipo.20562
Source: PubMed

ABSTRACT The hippocampus is involved in spatial memory processes, as established in a variety of species such as birds and mammals including humans. In humans, some hippocampal-dependent memory functions may be lateralized, the right hippocampus being predominantly involved in spatial navigation. In rodents, the question of possible lateralization remains open. Therefore, we first microdissected the CA1 subregion of the left and right dorsal hippocampi for analysis of mRNA expression using microarrays in rats having learnt a reference memory task in the Morris water-maze. Relative to untrained controls, 623 genes were differentially expressed in the right hippocampus, against only 74 in the left hippocampus, in the rats that had learnt the hidden platform location. Thus, in the right hippocampus, 299 genes were induced, 324 were repressed, and about half of them participate in signaling and transport, metabolism, and nervous system functions. In addition, most differentially expressed genes associated with spatial learning have been previously related to synaptic plasticity and memory. We then subjected rats to unilateral (left or right) or bilateral reversible functional inactivations in the dorsal hippocampus; lidocaine was infused either before each acquisition session or before retrieval of a reference spatial memory in the Morris water maze. We found that after drug-free acquisition, right or bilateral lidocaine inactivation (vs. left, or bilateral phosphate buffered saline (PBS) infusions) of the dorsal hippocampus just before a delayed (24 h) probe trial impaired performance. Conversely, left or bilateral hippocampus inactivation (vs. right, or bilateral PBS infusions) before each acquisition session weakened performance during a delayed, drug-free probe trial. Our data confirm a functional association between transcriptional activity within the dorsal hippocampus and spatial memory in the rat. Further, they suggest that there could be a leftward bias of hippocampal functions in engram formation or information transfer, and a rightward bias in spatial memory storage/retrieval processes.

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    • "However, when the lesion spares the ventral (temporal) part, learning remains possible (Moser et al., 1993, 1995), suggesting that although the ventral hippocampus contributes to learning, the dorsal hippocampus is required for optimal performance. This has been confirmed using temporal inactivation of the dorsal hippocampus (Hock and Bunsey, 1998; Bannerman et al., 1999; Pothuizen et al., 2004; Klur et al., 2009). The idea that the dorsal hippocampus is involved in spatial navigation is also supported by an electrophysiological study (Jung et al., 1994) as the proportion of cells exhibiting firing related to a specific place is lower in the ventral CA1 than in the dorsal area. "
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