title: Fiberoptic system for recording dendritic calcium signals in layer 5 neocortical pyramidal cells in freely moving rats.
abstract: Calcium influx into the dendritic tufts of layer 5 neocortical pyramidal neurons modifies a number of important cellular mechanisms. It can trigger local synaptic plasticity and switch the firing properties from regular to burst firing. Due to methodological limitations, our knowledge about Ca2+ spikes in the dendritic tuft stems mostly from in vitro experiments. However, it has been speculated that regenerative Ca2+ events in the distal dendrites correlate with distinct behavioral states. Therefore it would be most desirable to be able to record these Ca2+ events in vivo, preferably in the behaving animal. Here, we present a novel approach for recording Ca2+ signals in the dendrites of populations of layer 5 pyramidal neurons in vivo, which ensures that all recorded fluorescence changes are due to intracellular Ca2+ signals in the apical dendrites. The method has two main features: 1) bolus loading of layer 5 with a membrane-permeant Ca2+ dye resulting in specific loading of pyramidal cell dendrites in the upper layers and 2) a fiberoptic cable attached to a gradient index lens and a prism reflecting light horizontally at 90 degrees to the angle of the apical dendrites. We demonstrate that the in vivo signal-to-noise ratio recorded with this relatively inexpensive and easy-to-implement fiberoptic-based device is comparable to conventional camera-based imaging systems used in vitro. In addition, the device is flexible and lightweight and can be used for recording Ca2+ signals in the distal dendritic tuft of freely behaving animals.
authors.affiliation: Institute of Physiology, University of Bern, Bühlplatz 5, CH-3012 Bern, Switzerland.
authors.forename: Masanori
authors.initials: M
authors.lastname: Murayama
authors.forename: Enrique
authors.initials: E
authors.lastname: Pérez-Garci
authors.forename: Hans-Rudolf
authors.initials: HR
authors.lastname: Lüscher
authors.forename: Matthew E
authors.initials: ME
authors.lastname: Larkum
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002463:Cell Membrane Permeability; D003712:Dendrites / Q000502:physiology*; D005260:Female; D005336:Fiber Optic Technology / Q000379:methods*; D005453:Fluorescence; D009043:Motor Activity / Q000502:physiology*; D009473:Neuronal Plasticity; D017785:Photons; D017966:Pyramidal Cells / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology*; D013569:Synapses / Q000502:physiology
chemical_list: D002118:Calcium