Changes in the levels of hippocampal BDNF expression are accompanied with inflammatory dental pain-induced learning and memory impairment

Learning and memory requires a brain-derived neurotrophic factor (BDNF)-dependent phase in the hippocampus. It has been reported that chronic pain decreases hippocampal BDNF levels. We have also previously reported that noxious stimulation of the rat tooth pulp impairs learning and memory. Therefore, we decided to find the changes in the hippocampal BDNF expression which are associated with tooth pain and learning and memory impairment. Dental pulp nociception was induced by intradental injection of capsaicin (100μg) in male Wistar rats. BDNF expression levels were determined by semi-quantitative RT-PCR and western blotting. The data indicated that capsaicin elicited pain behaviors and impaired learning and memory in Morris water maze test. The protein and mRNA levels of BDNF were significantly (P<0.05) decreased in capsaicin-treated rats as compared with control animals. Furthermore, iboprofen (120mg/kg, ip) treatment caused a significant (P<0.05) up-regulation of the BDNF protein and mRNA in the hippocampus of capsaicin-injected animals. These findings suggest that inflammatory dental pain induces hippocampal function impairments by decreasing in BDNF expression.