Regulation of brain-derived neurotrophic factor transcripts by neuronal activation in rat hypothalamic neurons

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family and regulates the survival, differentiation, and maintenance of function i n different neuronal populations. BDNF is strongly expressed in hypothalami c neurons, where it exerts long- or short-lasting actions. Because glutamat e has been associated with regulations of hypothalamic hormones, we examine d the regulation of the four promoters of the BDNF gene by glutamate in fet al hypothalamic neurons. The expression levels of BDNF transcripts were inv estigated using semiquantitative RT-PCR. BDNF protein was determined by enz yme immunoassay, and BDNF and Trk B (BDNF receptor) gene variations were de termined by RNAse protection assay. By RT-PCR, we showed that, under basal conditions, BDNF transcripts from exons I, II, and III but not from IV were expressed in the hypothalamic neurons. Glutamate increased expression of b oth the protein and the four transcripts via N-methyl-D-aspartate receptors , with maximal stimulations after 3 hr of application for exon I and II mRN As and after 1 hr for exon III and IV mRNAs. Actinomycin D blocked the incr ease of all transcripts, whereas cycloheximide treatment inhibited stimulat ion only of exon I and II mRNAs. Trk B. mRNA was rapidly and transiently re duced after glutamate application. Our results demonstrate that glutamate 1 ) regulates BDNF mRNA expression at an early developmental stage in hypotha lamic neurons and 2) exerts a differential regulation of BDNF transcripts. (C) 2001 Wiley-Liss, Inc.