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On the photovoltaic effect in localfield potential recordings
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Developmental Genetics.
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Developmental Genetics.
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2016 (English)In: Neurophotonics, ISSN 2329-423X, Vol. 3, no 1, 015002Article in journal (Refereed) Published
Abstract [en]

ptogenetics allows light activation of genetically defined cell populations and the study of their link to specific brain functions. While it is a powerful method that has revolutionized neuroscience in the last decade, the shortcomings of directly stimulating electrodes and living tissue with light have been poorly characterized. Here, we assessed the photovoltaic effects in local field potential (LFP) recordings of the mouse hippocampus. We found that light leads to several artifacts that resemble genuine LFP features in animals with no opsin expression, such as stereotyped peaks at the power spectrum, phase shifts across different recording channels, coupling between low and high oscillation frequencies, and sharp signal deflections that are detected as spikes. Further, we tested how light stimulation affected hippocampal LFP recordings in mice expressing channelrhodopsin 2 in parvalbumin neurons (PV/ChR2 mice). Genuine oscillatory activity at the frequency of light stimulation could not be separated from light-induced artifacts. In addition, light stimulation in PV/ChR2 mice led to an overall decrease in LFP power. Thus, genuine LFP changes caused by the stimulation of specific cell populations may be intermingled with spurious changes caused by photovoltaic effects. Our data suggest that care should be taken in the interpretation of electrophysiology experiments involving light stimulation.

Place, publisher, year, edition, pages
2016. Vol. 3, no 1, 015002
National Category
URN: urn:nbn:se:uu:diva-279326DOI: 10.1117/1.NPh.3.1.015002ISI: 000373771200006PubMedID: 26835485OAI: diva2:907843
Available from: 2016-02-29 Created: 2016-02-29 Last updated: 2016-06-20Bibliographically approved
In thesis
1. On the Mechanisms Behind Hippocampal Theta Oscillations: The role of OLMα2 interneurons
Open this publication in new window or tab >>On the Mechanisms Behind Hippocampal Theta Oscillations: The role of OLMα2 interneurons
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Theta activity is one of the most prominent rhythms in the brain and appears to be conserved among mammals.  These 4-12 Hz oscillations have been predominantly studied in the dorsal hippocampus where they are correlated with a broad range of voluntary and exploratory behaviors. Theta activity has been also implicated in a number of mnemonic processes, long-term potentiation (LTP) induction and even acting as a global synchronizing mechanism. Moving along the dorso-ventral axis theta activity is reduced in power and desynchronized from the dorsal part. However, theta activity can also be generated in the ventral hippocampus itself during anxiety- and fear-related behaviors. Until now it was unknown which hippocampal cell population was capable to generate theta activity and it was controversial if its origin was local, in the hippocampus, or driven by other brain regions. In this thesis I present compelling in vitro and in vivo  evidence that   a subpopulation of OLM interneurons (defined by the Chrna2-cre line)  distinctively enriched  in the CA1 region of  the ventral hippocampus is implicated in LTP function (paper I,II), information control (paper V) and the induction of theta activity that is under cholinergic  control (paper IV). Importantly, a concomitant effect of the optogenetically induced theta activity is reduction in anxiety (Paper IV). Another innovation of this work was the development of a methodological approach to avoid artefactual signals when combining electrophysiology with light activation during optogenetic experiments (Paper III). In summary, the work presented in this thesis elucidates the role of a morphologically and electrophysiologially identified cell population, OLMα2 interneurons, first on the cellular, then on the circuit and ultimately on the behavioral level.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 47 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1206
hippocampus, interneuron, optogenetics, theta oscillations, anxiety
National Category
urn:nbn:se:uu:diva-282144 (URN)978-91-554-9542-8 (ISBN)
Public defence
2016-05-28, A1:111a, Husargatan 3, Uppsala, 09:15 (English)
Available from: 2016-05-04 Created: 2016-04-03 Last updated: 2016-05-12

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