Oroxylin A increases BDNF production by activation of MAPK-CREB pathway in rat primary cortical neuronal culture.

Oroxylin A (5,7-dihydroxy-6-methoxyfavone) is a flavonoid compound originated from the root of Scutellaria baicalensis Georgi. Our previous reports suggested that oroxylin A improves memory function in rat, at least in part, by its antagonistic effects on GABA(A) receptor. In addition, oroxylin A protects neurons from ischemic damage by mechanisms currently not clear. In this study we determined whether oroxylin A modulates the level of brain derived neurotrophic factor (BDNF) in primary rat cortical neuronal culture, which is well known for its role on neuronal survival, neurogenesis, differentiation of neurons and synapses and learning and memory. Treatment of oroxylin A for 3-48h increased BDNF expression which was analyzed by ELISA assay and Western blot analysis. Oroxylin A induced slow but sustained increases in intracellular calcium level and activated ERK1/2 mitogen activated protein kinase (MAPK). In addition, oroxylin A phosphorylated cyclic AMP response element binding protein (CREB) at Ser 133 in concentration and time dependent manner. Pretreatment with the MAPK inhibitor PD98059 (10µM) attenuated phosphorylation of ERK1/2 and CREB as well as BDNF production, which suggests that oroxylin A regulates BDNF production by activating MAPK-CREB pathway. GABA(A) antagonist bicuculline mimicked the effects of oroxylin A on BDNF production as well as MAPK-CREB pathway. Increase in intracellular Ca(2+) concentration, phosphorylation of ERK1/2 and CREB, and BDNF expression by oroxylin A was blocked by NMDA receptor inhibitor MK-801 (10µM) as well as tetrodotoxin (TTX, 0.5 and 1µM). The results from the present study suggest that the calcium and p-CREB dependent induction of BDNF expression, possibly via activation of synaptic NMDA receptor through the blockade of GABA(A) activity in cortical neuronal circuitry, might be responsible for the neuroprotective or memory enhancing effects of oroxylin A.

Prenatal exposure of ethanol induces increased glutamatergic neuronal differentiation of neural progenitor cells.

BACKGROUND: Prenatal ethanol exposure during pregnancy induces a spectrum of mental and physical disorders called fetal alcohol spectrum disorder (FASD). The central nervous system is the main organ influenced by FASD, and neurological symptoms include mental retardation, learning abnormalities, hyperactivity and seizure susceptibility in childhood along with the microcephaly. In this study, we examined whether ethanol exposure adversely affects the proliferation of NPC and de-regulates the normal ratio between glutamatergic and GABAergic neuronal differentiation using primary neural progenitor culture (NPC) and in vivo FASD models. METHODS: Neural progenitor cells were cultured from E14 embryo brain of Sprague-Dawley rat. Pregnant mice and rats were treated with ethanol (2 or 4 g/kg/day) diluted with normal saline from E7 to E16 for in vivo FASD animal models. Expression level of proteins was investigated by western blot analysis and immunocytochemical assays. MTT was used for cell viability. Proliferative activity of NPCs was identified by BrdU incorporation, immunocytochemistry and FACS analysis. RESULTS: Reduced proliferation of NPCs by ethanol was demonstrated using BrdU incorporation, immunocytochemistry and FACS analysis. In addition, ethanol induced the imbalance between glutamatergic and GABAergic neuronal differentiation via transient increase in the expression of Pax6, Ngn2 and NeuroD with concomitant decrease in the expression of Mash1. Similar pattern of expression of those transcription factors was observed using an in vivo model of FASD as well as the increased expression of PSD-95 and decreased expression of GAD67. CONCLUSIONS: These results suggest that ethanol induces hyper-differentiation of glutamatergic neuron through Pax6 pathway, which may underlie the hyper-excitability phenotype such as hyperactivity or seizure susceptibility in FASD patients.