Molecular basis of chronic stress-induced hippocampal lateral asymmetry in rats and impact on learning and memory

Neurochemical lateralization has been demonstrated in the rat brain suggesting that such lateralization might contribute to behavior. Thus, the aim of the present study was to examine neurochemical asymmetry in the hippocampus, molecular basis of neurochemical lateralization and its impact on spatial learning and memory. Changes in noradrenaline content, tyrosine hydroxylase (TH) were studied in the right and left hippocampus of naive control and chronically isolated rats, by applying TaqMan RT-PCR and Western blot analysis. Hippocampal-based spatial learning and memory were evaluated using the Barnes maze. In control rats an asymmetrical right-left distribution of noradrenaline content and gene expression of catecholamine synthesizing enzyme was found. Chronic psychosocial stress further emphasized asymmetry. Isolation stress reduced noradrenaline content only in the right hippocampus. No changes were observed in gene expression and protein levels of TH in the right hippocampus, whereas expression of catecholamine synthesizing enzyme was elevated in the left hippocampus. Reduced noradrenaline content in the right hippocampus did not cause impairment in spatial learning and memory. Our findings suggest that chronic psychosocial stress reduces noradrenaline stores in the right hippocampus which may be caused by molecular asymmetry, but it does not affect spatial learning and memory.