title: Competition and Homeostasis of Excitatory and Inhibitory Connectivity in the Adult Mouse Visual Cortex.
abstract: During cortical development, synaptic competition regulates the formation and adjustment of neuronal connectivity. It is unknown whether synaptic competition remains active in the adult brain and how inhibitory neurons participate in this process. Using morphological and electrophysiological measurements, we show that expressing a dominant-negative form of the TrkB receptor (TrkB.T1) in the majority of pyramidal neurons in the adult visual cortex does not affect excitatory synapse densities. This is in stark contrast to the previously reported loss of excitatory input which occurs if the exact same transgene is expressed in sparse neurons at the same age. This indicates that synaptic competition remains active in adulthood. Additionally, we show that interneurons not expressing the TrkB.T1 transgene may have a competitive advantage and obtain more excitatory synapses when most neighboring pyramidal neurons do express the transgene. Finally, we demonstrate that inhibitory synapses onto pyramidal neurons are reduced when TrkB signaling is interfered with in most pyramidal neurons but not when few pyramidal neurons have this deficit. This adjustment of inhibitory innervation is therefore not a cell-autonomous consequence of decreased TrkB signaling but more likely a homeostatic mechanism compensating for activity changes at the population level.
authors.affiliation: Department of Molecular Visual Plasticity, The Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam 1105, The Netherlands.
authors.forename: M Hadi
authors.initials: MH
authors.lastname: Saiepour
authors.affiliation: Department of Molecular Visual Plasticity, The Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam 1105, The Netherlands.
authors.forename: Sridhara
authors.initials: S
authors.lastname: Chakravarthy
authors.affiliation: Department of Molecular Visual Plasticity, The Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam 1105, The Netherlands.
authors.forename: Rogier
authors.initials: R
authors.lastname: Min
authors.affiliation: Department of Molecular Visual Plasticity, The Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam 1105, The Netherlands.
authors.forename: Christiaan N
authors.initials: CN
authors.lastname: Levelt
mesh_terms: D000200:Action Potentials; D000818:Animals; D049229:Dendritic Spines / Q000378:metabolism; D019706:Excitatory Postsynaptic Potentials; D006706:Homeostasis; D053444:Inhibitory Postsynaptic Potentials; D007395:Interneurons / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D055369:Miniature Postsynaptic Potentials; D017966:Pyramidal Cells / Q000378:metabolism / Q000502:physiology*; D020813:Receptor, trkB / Q000235:genetics / Q000378:metabolism*; D018091:Receptors, AMPA / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism; D015398:Signal Transduction; D013569:Synapses / Q000378:metabolism / Q000502:physiology; D014793:Visual Cortex / Q000378:metabolism / Q000502:physiology*
chemical_list: D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate; D020813:Receptor, trkB
keywords: BDNF; TrkB; cell autonomous; inhibition; parvalbumin