Occlusal disharmony suppresses long-term potentiation in the rat hippocampal CA1 region
PURPOSE: Recent studies have shown that occlusal disharmony (OD) causes deterioration in learning and memory via neuropathological processes in the mouse hippocampus.
METHODS: To elucidate the mechanism(s) by which this deterioration occurs, we examined the effect of a bite-raised condition, which induced OD, on long-term potentiation (LTP) in the rat hippocampal CA1 region. In addition, plasma levels of corticosterone and catecholamines, body weight, and food intake were measured to evaluate the involvement of the hypothalamic-pituitary-adrenal (HPA) axis and/or the sympathetic-adrenergic-medullary (SAM) system.
RESULTS: Ten days after bite-raising surgery, the amplitude of LTP was reduced by 62% in rats that underwent OD compared to sham-operated rats. The OD condition also caused a significant elevation in plasma levels of corticosterone and norepinephrine compared to control rats. Body weight decreased in OD rats, but the amount of food intake was not different between bite-raised and control conditions.
CONCLUSION: These findings suggest that a disharmonious occlusal condition in rats induces not only impaired hippocampal plasticity but also chronic activation of the HPA axis and modulation of the autonomic nervous system.