Occlusal Disharmony Transiently Impairs Learning and Memory in the Mouse by Increasing Dynorphin A Levels in the Amygdala

Abstract

Occlusal disharmony sometimes causes not only stiffness of neck but also psychiatric depression, suggesting that the condition of oral cavity may affect the central nervous system. Dynorphin A is an endogenous opioid peptide that specifically binds the κ-opioid receptor and has a protective role against stress. Dynorphinergic nervous system is intensely distributed in the amygdala and hippocampus that are coping areas with stress. As a model of malocclusion, we placed dental resin on the molars to increase the occlusal vertical dimension (bite-raise). After various survival times, we analyzed the amygdala and hippocampus by immunohistochemistry and immunosorbent assay (ELISA). Furthermore, the effects on learning and memory were assessed by Morris water maze test. In the amygdala, the levels of dynorphin A were increased on the 1st day after increasing the vertical dimension as indicated by immunohistochemical and ELISA assessments. The levels of dynorphin A returned to control levels on the 5th day. In the hippocampus, there were no noticeable changes in dynorphin A levels. The water maze test indicated that increasing the vertical dimension caused longer escape latency times on the 3rd day compared to those of sham-operated group. However, the bite-raised mice treated with a dynorphin antagonist, nor-binaltorphimine, showed similar escape latency times to the times of sham-operated group, even on the 3rd day. These results suggest that occlusal disharmony causes stress resulting in a transient increase of dynorphin A levels at least in the amygdala and that the increased dynorphin A levels transiently impair learning and memory.

Difference of brain-derived neurotrophic factor expression and pyramid cell count during mastication of food with varying hardness

“…14 These findings also corroborate to another study by Okihara, et al 7 (2014), which found a memory impairment accompanied by low number of neuron cells in the hippocampus after long-term soft diet. 7 Previous studies on mastication impaired animal models through tooth extraction 22 , 23 , bite-raise 24 , 25 and long-term soft diets 7 , 26 found that these aspects may alter hippocampus learning and memory function. Other studies also proved that impaired function of the hippocampus due to long-term soft diet could be improved by providing a hard diet.…”

Ester Hydrolysis Differentially Reduces Aconitine-Induced Anti-hypersensitivity and Acute Neurotoxicity: Involvement of Spinal Microglial Dynorphin Expression and Implications for Aconitum Processing

“…Based on the manufacturer’s information, the dynorphin A antiserum was specific to dynorphin A (100%), but not to dynorphin B (0%), β-endorphin (0%), α–neo-endorphin (0%), or leu-enkephalin (0%). Its specificity was also validated by the antigen absorption test by other laboratories ( Wakabayashi et al, 2010 ; Yamada et al, 2013 ).…”

Effect of social isolation stress on saliva BDNF in rat

“…Following this, the rats were euthanized. Blood (serum and plasma) and brain (hippocampus, prefrontal cortex, and amygdala) samples were collected, as described previously [25], then stored at −80°C until further analysis.…”