An epigenetic induction of a right‐shift in hippocampal asymmetry: Selectivity for short‐ and long‐term potentiation but not post‐tetanic potentiation

Abstract

In humans, it is well established that major psychological functions are asymmetrically represented between the left and right cerebral cortices. The developmental origin of such functional lateralization remains unknown. Using the rat as a model system, we examined whether exposing neonates briefly to a novel environment can differentially affect synaptic plasticity in the left and right hippocampi during adulthood. During the first 3 weeks of life, one half of the pups from a litter spent 3 min daily away from their familiar home environment (Novel) while their littermates remained in that familiar environment (Home). At adulthood (7-months old), post-tetanic potentiation (PTP) of excitatory post-synaptic potentials (EPSPs), a very short-lasting form of plasticity, was greater among the Novel than the Home rats in both left and right hippocampi. In contrast, the novelty-induced increases in short- and long-term potentiation (STP, LTP), two relatively longer-lasting forms of plasticity, were found only in the right hippocampus. These findings demonstrate that a phase-selective asymmetry in hippocampal synaptic plasticity can be induced epigenetically by seemingly small systematic differences in early life environment. The selectivity of this asymmetry for the longer-lasting forms of synaptic plasticity suggests that the observed asymmetry in plasticity may contribute specifically to an asymmetric learning process which, in turn, may contribute to a functional asymmetry in the neocortex.

Longitudinal in vivo Diffusion Tensor Imaging Detects Differential Microstructural Alterations in the Hippocampus of Chronic Social Defeat Stress-Susceptible and Resilient Mice

“…Glucocorticoids may cause the lateral effect of stress on the hippocampus, which has been predominantly observed in the right side (Tang et al, 2008; Zach et al, 2010, 2016; Frodl and O’Keane, 2012). However, higher HPA axis activation (basal cortisol levels) has been found to be associated with higher left relative to right hippocampal MD, suggesting that either the left hippocampus plays a lateralized regulatory role in HPA axis function or the neuroendocrine response under stress imposes left-sided effects on hippocampal microstructure (Madsen et al, 2012).…”

Altered amygdala and hippocampus effective connectivity in mild cognitive impairment patients with depression: a resting-state functional MR imaging study with granger causality analysis

“…Thirdly, the use of medication was probably an important confounding factor for the reorganization of brain functional network [46]. Fourthly, it has been reported that the two hemispheres of the human brain differ in their anatomy and function, thus whether there was any asymmetry in effective functional connectivity between the left and right occipital lobe should be taken account into in the future study [47]. Lastly, our study focused on the effect of MDD on aMCI, further studies on the effect of aMCI on MDD are expected in future.…”

Childhood maltreatment is associated with reduced volume in the hippocampal subfields CA3, dentate gyrus, and subiculum

“…The volume of the CA1-CA3, DG, and subiculum were substantially reduced but only on the right side. Similarly, neonatal exposure to novelty in LongEvans rats (a potentially beneficial experience) was found in adulthood to increase right hippocampal volume (64) and to augment short-and long-term potentiation in the right but not left hippocampus (65). Unfortunately, few translational studies examining stress-related effects on the hippocampus provide information on laterality.…”