Altered balance of glutamatergic/GABAergic synaptic input and associated changes in dendrite morphology after BDNF expression in BDNF-deficient hippocampal neurons.
Cultured neurons from bdnf-/- mice display reduced densities of synaptic terminals, although in vivo these deficits are small or absent. Here we aimed at clarifying the local responses to postsynaptic brain-derived neurotrophic factor (BDNF). To this end, solitary enhanced green fluorescent protein (EGFP)-labeled hippocampal neurons from bdnf-/- mice were compared with bdnf-/- neurons after transfection with BDNF, bdnf-/- neurons after transient exposure to exogenous BDNF, and bdnf+/+ neurons in wild-type cultures. Synapse development was evaluated on the basis of presynaptic immunofluorescence and whole-cell patch-clamp recording of miniature postsynaptic currents. It was found that neurons expressing BDNF::EGFP for at least 16 h attracted a larger number of synaptic terminals than BDNF-deficient control neurons. Transfected BDNF formed clusters in the vicinity of glutamatergic terminals and produced a stronger upregulation of synaptic terminal numbers than high levels of ambient BDNF. Glutamatergic and GABAergic synapses reacted differently to postsynaptic BDNF: glutamatergic input increased, whereas GABAergic input decreased. BDNF::EGFP-expressing neurons also differed from BDNF-deficient neurons in their dendrite morphology: they exhibited weaker dendrite elongation and stronger dendrite initiation. The upregulation of glutamatergic synaptic input and the BDNF-induced downregulation of GABAergic synaptic terminal numbers by postsynaptic BDNF depended on tyrosine receptor kinase B activity, as deduced from the blocking effects of K252a. The suppression of dendrite elongation was also prevented by block of tyrosine receptor kinase B but required, in addition, glutamate receptor activity. Dendritic length decreased with the number of glutamatergic contacts. These results illuminate the role of BDNF as a retrograde synaptic regulator of synapse development and the dependence of dendrite elongation on glutamatergic input.
Singh
B
B
Developmental Physiology Group, Johannes Mueller Institute for Neurophysiology, University Medical School (Charité) of the Humboldt University, D-10117 Berlin, Germany.
Henneberger
C
C
Betances
D
D
Arevalo
M A
MA
Rodríguez-Tébar
A
A
Meier
J C
JC
Grantyn
R
R
D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D003712:Dendrites / Q000502:physiology*; D004815:Epidermal Growth Factor / Q000235:genetics; D005260:Female; D015870:Gene Expression / Q000502:physiology; D018698:Glutamic Acid / Q000502:physiology*; D006624:Hippocampus / Q000166:cytology / Q000254:growth & development / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009473:Neuronal Plasticity / Q000502:physiology; D009474:Neurons / Q000502:physiology / Q000648:ultrastructure; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D020800:Receptor, Nerve Growth Factor / Q000502:physiology; D020813:Receptor, trkB / Q000502:physiology; D013569:Synapses / Q000502:physiology*; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D019208:Brain-Derived Neurotrophic Factor; D020800:Receptor, Nerve Growth Factor; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D004815:Epidermal Growth Factor; D020813:Receptor, trkB