Chapter 4 Cre-Mediated Transduction of Neurons CHAPTER 4 Postsynaptic TrkB-Signaling Has Distinct Roles in Spine Maintenance in Adult Visual Cortex and Hippocampus

In adult primary visual cortex (V1), dendritic spines are more persistent than during development. Brain-derived neurotrophic factor (BDNF) increases synaptic strength and its levels rise during cortical development. We therefore asked whether postsynaptic BDNF-signaling through its receptor TrkB regulates spine persistence in adult V1. This question has been difficult to address as most methods utilized to alter TrkB-signaling in vivo affect cortical development or cannot distinguish between preand postsynaptic mechanisms. We circumvented these problems by employing transgenic mice expressing a dominant negative TrkB-EGFP fusion protein in sparse pyramidal neurons of the adult neocortex and hippocampus producing a Golgi-staining like pattern. In adult V1 this resulted in reduced mushroom spine maintenance and synaptic efficacy accompanied by an increase in long and thin spines and filopodia. In contrast, mushroom spine maintenance was unaffected in CA1, indicating that TrkB plays fundamentally different roles in structural plasticity in these brain areas.