Brain-Derived Neurotrophic Factor Mediates Activity-Dependent Dendritic Growth in Nonpyramidal Neocortical Interneurons in Developing Organotypic Cultures

Abstract

Brain-derived neurotrophic factor (BDNF) promotes postnatal maturation of GABAergic inhibition in the cerebral and cerebellar cortices, and its expression and release are enhanced by neuronal activity, suggesting that it acts in a feedback manner to maintain a balance between excitation and inhibition during development. BDNF promotes differentiation of cerebellar, hippocampal, and neostriatal inhibitory neurons, but its effects on the dendritic development of neocortical inhibitory interneurons remain unknown. Here, we show that BDNF mediates depolarization-induced dendritic growth and branching in neocortical interneurons. To visualize inhibitory interneurons, we biolistically transfected organotypic cortical slice cultures from neonatal mice with green fluorescent protein (GFP) driven by the glutamic acid decarboxylase (GAD)67 promoter. Nearly all GAD67-GFP-expressing neurons were nonpyramidal, many contained GABA, and some expressed markers of neurochemically defined GABAergic subtypes, indicating that GAD67-GFP-expressing neurons were GABAergic. We traced dendritic trees from confocal images of the same GAD67-GFP-expressing neurons before and after a 5 d growth period, and quantified the change in total dendritic length (TDL) and total dendritic branch points (TDBPs) for each neuron. GAD67-GFP-expressing neurons growing in control medium exhibited a 20% increase in TDL, but in 200 ng/ml BDNF or 10 mm KCl, this increase nearly doubled and was accompanied by a significant increase in TDBPs. Blocking action potentials with TTX did not prevent the BDNF-induced growth, but antibodies against BDNF blocked the growth-promoting effect of KCl. We conclude that BDNF, released by neocortical pyramidal neurons in response to depolarization, enhances dendritic growth and branching in nearby inhibitory interneurons.

Single-Cell Characterization of Retrograde Signaling by Brain-Derived Neurotrophic Factor

“…Regulated release of BDNF has been shown to be critical for functions ranging from neurite outgrowth and spine formation (McAllister et al, 1996;Tyler and Pozzo-Miller, 2001;Horch and Katz, 2002;Jin et al, 2003) to short-and long-lasting forms of synaptic plasticity (Nagappan and Lu, 2005) to learning and cognition (Tyler et al, 2002;Egan et al, 2003;Hariri et al, 2003;Rybakowski et al, 2003). The mechanisms of this release are gradually being better understood as the molecular interactions responsible for regulated release are identified (Chen et al, 2005;Lou et al, 2005), but numerous functional issues remain to be clarified.…”

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.…”

“…AMPA currents in TGFα/ BDNF-treated culture were indistinguishable from those of untreated cultures. BDNF treatment caused an increase in membrane capacitance of the multipolar-type neurons, which presumably reflect an increase in somatic diameter and/or neurite length (McAllister et al, 1995;Jin et al, 2003;Nagano et al, 2003) (Table 2). Co-application with TGFα, however, failed to influence this activity of BDNF.…”

Effects of chronic network hyperexcitability on the growth of hippocampal dendrites

“…Each type of experiment was repeated on three separate occasions and results combined for final analysis. Similar combined confocal imaging and neuron reconstructions have been performed in the past to quantify experimentally-induced alterations in dendrite arbors (Redmond et al, 2002;Jin et al, 2003) and is advantageous over more traditional biocytin reconstructions which require time-consuming whole cell recordings to fill individual cells.…”