Accelerated dendritic development of rat cortical pyramidal cells and interneurons after biolistic transfection with BDNF and NT4/5

Abstract

Neurotrophins are candidate molecules for regulating dendritogenesis. We report here on dendritic growth of rat visual cortex pyramidal and interneurons overexpressing `brain-derived neurotrophic factor' BDNF and`neurotrophin 4/5' NT4/5. Neurons in organotypic cultures were transfected with plasmids encoding either `enhanced green fluorescent protein' EGFP,BDNF/EGFP or NT4/5/EGFP either at the day of birth with analysis at 5 days in vitro, or at 5 days in vitro with analysis at 10 days in vitro.In pyramidal neurons, both TrkB ligands increased dendritic length and number of segments without affecting maximum branch order and number of primary dendrites. In the early time window, only infragranular neurons were responsive. Neurons in layers II/III became responsive to NT4/5, but not BDNF,during the later time window. BDNF and NT4/5 transfectants at 10 days in vitro had still significantly shorter dendrites than adult pyramidal neurons,suggesting a massive growth spurt after 10 days in vitro. However, segment numbers were already in the range of adult neurons. Although this suggested a role for BDNF, long-term activity-deprived, and thus BDNF-deprived, pyramidal cells developed a dendritic complexity not different from neurons in active cultures except for higher spine densities on neurons of layers II/III and VI. Neutralization of endogenous NT4/5 causes shorter and less branched dendrites at 10 days in vitro suggesting an essential role for NT4/5. Neutralization of BDNF had no effect. Transfected multipolar interneurons became identifiable during the second time window. Both TrkB ligands significantly increased number of segments and branch order towards the adult state with little effects on dendritic length. The results suggested that early in development BDNF and NT4/5 probably accelerate dendritogenesis in an autocrine fashion. In particular, branch formation was advanced towards the adult pattern in pyramidal cells and interneurons.

BDNF stabilizes synapses and maintains the structural complexity of optic axons in vivo

“…Evidence that TrkB signaling is necessary for neurotransmitter receptor maintenance suggest that BDNF may stabilize synapses or synaptic components (Gonzalez et al, 1999). That BDNF is required not only for the formation (Horch and Katz, 2002;McAllister et al, 1995;Wirth et al, 2003) but also for the maintenance of dendritic structure (Gorski et al, 2003) further supports a role for BDNF in synapse stabilization. However, studies that examine the long-term effects of manipulating BDNF or TrkB expression in mammalian embryos or in slice cultures cannot directly differentiate between synapse formation and synapse stabilization.…”

Transforming growth factor alpha attenuates the functional expression of AMPA receptors in cortical GABAergic neurons

“…TGFα appeared to have a competitive role against conventional neurotrophic factor in the regulation of GluR1 subunit expression. BDNF also increases whole-cell capacitance in cultured neurons, which presumably represents an increase in soma size and/or neurite length (Jin et al, 2003;Widmer and Hefti, 1994;Wirth et al, 2003). Co-treatment with TGFα, however, failed to counteract this action of BDNF.…”

Control of Dendritic Arborization by the Phosphoinositide-3′-Kinase–Akt–Mammalian Target of Rapamycin Pathway

“…BDNF is a physiological activator of Ras-PI3K pathways in neurons and has been implicated in dendrite development (McAllister et al, 1995;Horch and Katz, 2002;Tolwani et al, 2002;Wirth et al, 2003). We tested whether BDNF might act via the Ras-PI3K-Akt pathway to regulate dendrite morphogenesis.…”