Effect And Mechanism Of Baicalein On Synaptic Plasticity Of CA1 Subfield In Rat Hippocampal Slices

Part 1. Effects of BAI on synaptic plasticity of CA1 subfield in rat hippocampal slicesBackground: Baicalein is one of the major flavonoids extracted from the dried root of Scutellaria baicalensis Georgi (Huangqin). It has been widely used as an antibacterial and antiviral agent. Previous research has demonstrated that baicalein is a free radical scavenger and a selective inhibitor of 12-lipoxygenase. Total flavonoids isolated from Scutellaria baicalensis Georgi has been shown to improve memory impairment and chemical neuronal damage. Recently, several studies have demonstrated effects of mixtures of flavonoids on learning and memory and long-term potentiation (LTP). However, no detailed studies have been performed concerning the impact of BAI on LTP of CA1 subfield in rat hippocampal slices. The aim of the current investigation was to characterize the role of BAI on long-term potentiation (LTP) in the CA1 region of rat hippocampal slices and to elucidate the molecular sequence of events leading to these changes. Methods: Using hippocampal slice preparations and electrophysiology recording, we investigated the effects of BAI on fEPSP, PPR, I/O curve and LTP of CA1 subfield. Results: BAI did not affect basal synaptic transmission in normal slices at low concentration. However, administration of 100μmol/L BAI enhanced fEPSP in CA1 subfield significantly. LTP was enhanced by incubation of 10μmol/L BAI significantly. We found that administration of BAI did not alter the presynaptic glutamate release in response to both single pulse and tetanic stimulation. NMDA receptor antagonist APV blocked BAI-facilitated LTP. Pre-treatment of slices with verapamil had no significant effect on BAI-facilitated LTP. Calcium chelator BAPTA-AM prevented BAI-facilitated LTP significantly. Conclusion: These findings demonstrate that the natural product BAI facilitated LTP is dependent on NMDA receptors and [Ca2+] i. Part 2. Effects of BAI on plasticity-related proteins of CA1 subfield in rat hippocampal slicesBackground: Neurogranin (Ng) is a neural-specific CaM-binding protein that is a substrate for PKC. Ng is implicated in the modulation of Ca2+ and Ca2+/CaM-mediated signaling pathways. CaMKII is a major class of Ca2+/calmodulin-dependent protein kinases in the brain that contributes to various neuronal processes, associated with learning and memory formation. Interestingly, CaMKII contains an autophosphorylation site at threonine 286, the phosphorylation of which generates a Ca2+/CaM-independent, autonomously active form of CaMKII (pThr286-CaMKII). Through this mechanism, pCaMKII can evoke prolonged physiological responses triggered by transient increases in [Ca2+]i. It is clear that CaMKII is required as a mediator for NMDA receptor-dependent LTP. The aim of this study is to test the role of Ng and CaMKII in BAI-facilitated LTP. Methods: Western blot technique was employed to analyze the changes of CaMKII and Ng levels after BAI treatment and HFS stimulation. Results: 10μmol/L BAI increased the ratio of pCaMKIIα/CaMKII and pNg/Ng after HFS stimulation, measured in the total homogenate of hippocampal CA1 area. Conclusion: BAI-facilitated LTP was associated with increases in the expression of pCaMKII and pNg.