Distinct subcellular localization of BDNF transcripts in cultured hypothalamic neurons and modification by neuronal activation

We investigated subcellular localization of total brain-derived neurotrophic factor (BDNF) mRNA (panBDNF) and its different 5' exon-specific transcripts in cultured hypothalamic neurons. Non-isotopic in situ hybridization (DIG-labeled exon-specific riboprobes) associated with immunocytochemical MAP2 or GFAP labeling was used for detection. We found that under basal conditions panBDNF mRNA was localized in neuronal soma and in primary dendritic processes. Transcripts I and II were weakly expressed in neuronal soma while transcripts IV and VI mRNA were strongly expressed. panBDNF mRNA and transcript VI mRNA were detected in proximal dendritic processes and in astrocytes. N-methyl-d-aspartate (NMDA) treatment decreased the dendritic label of panBDNF and transcript VI mRNA. In contrast, MK-801 (NMDA antagonist) treatment extended the labeling of all the transcripts in dendrites while K+ depolarization only extended the dendritic labeling of panBDNF and transcript VI mRNAs. These results suggest a NMDA-receptor dependent inhibitory mechanism for dendritic destination of BDNF transcripts in hypothalamic neurons.