Intraventricular Infusion of TrkB-Fc Fusion Protein Promotes Ischemia-Induced Neurogenesis in Adult Rat Dentate Gyrus

Abstract

Background and Purpose - We have previously shown that delivery of brain-derived neurotrophic factor (BDNF) through direct intrahippocampal gene transduction with a viral vector suppresses the formation of new dentate granule cells triggered by global forebrain ischemia. Here, we investigated whether inhibition of endogenous BDNF alters ischemia-induced neurogenesis in the dentate gyrus. Methods - Rats were subjected to 30 minutes of global forebrain ischemia and then received intraventricular infusion of either the BDNF scavenger, TrkB-Fc fusion protein, or control Hu-Fc for 2 weeks. In parallel, all animals were injected intraperitoneally with the mitosis marker 5-bromo-2′-deoxyuridine-5′-monophosphate (BrdU). Animals were killed at 2 or 6 weeks after the ischemic insult, and neurogenesis was then assessed immunocytochemically with epifluorescence or confocal microscopy. Results - Infusion of TrkB-Fc fusion protein gave rise to elevated numbers of ischemia-generated new neurons, double-labeled with BrdU and the early neuronal marker Hu or the mature neuronal marker NeuN, in the dentate subgranular zone and granule cell layer at 2 and 6 weeks after the insult. Conclusions - Our findings provide evidence that endogenous BDNF counteracts neuronal differentiation, but not cell proliferation or survival, in ischemia-induced dentate gyrus neurogenesis.