Novel method for closed-loop electroretinogram measurement of sensitivity in Drosophila
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1
Ludwig-Maximilians-Universität München, Department Biology II, Germany
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2
Max-Planck-Institut für Neurobiologie Martinsried, Germany
In the compound eye of Drosophila, the six outer photoreceptors (R1-R6) of each ommatidium express rhodopsin 1 as their light sensing pigment. The inner photoreceptors R7 and R8 express one of four opsins (rhodopsin 3,4,5, and 6) with different spectral sensitivities and show different response dynamics. Spectral sensitivity of these rhodopsins has been determined in electroretinogram measurements (ERG) using the closed-loop voltage clamp technique [1]. In this technique, the intensity of a light source, flickering at around 10Hz, is adjusted such that the receptor response matches a predefined criterion level. However, since direct measurement of the receptor response amplitude under these conditions is unreliable, the standard deviation of the response during the stimulation period is typically taken as the target signal [2]. This protocol was established for electroretinogram (ERG) recordings from flies with functional outer photoreceptors R1-R6. Using flies lacking functional outer receptors, we recorded signals from inner photoreceptors R7 and/or R8. Because of the smaller signal size, a drift in baseline and the differences in response dynamics in these receptors compared to the outer receptors, we found this protocol to be inadequate for these measurements. Here we present a novel ERG protocol - Interleaved Reference Electroretinogram (INTER ERG) - that is able to reliably estimate the receptor potential amplitude directly. This method makes use of a reference light stimulus, which is activated in alternation with the test stimulus in an interleaved stimulus-reference design. The test stimulus light intensity is adjusted such that the ERG amplitude matches that evoked by the reference light. This protocol circumvents the problem of a drifting baseline [2] and furthermore yields reliable and comparable sensitivities independent of individual response differences. We show detailed data on the working range of the technique and furthermore present an ERG Plugin for RELACS [3,4] - a framework for closed loop electrophysiological experiments - developed to support standard ERG recordings as well as INTER ERG.
References
[1] Franceschini, N. „Voltage clamp by light“. Invest Opthalmol [Suppl 5] (1979).
[2] Salcedo, E., Huber A., Henrich S., Chadwell L., Chou W., Paulsen R., und Britt S. „Blue- and Green-Absorbing Visual Pigments of Drosophila: Ectopic Expression and Physiological Characterization of the R8 Photoreceptor Cell-Specific Rh5 and Rh6 Rhodopsins“. J. Neurosci. 19, Nr. 24: 10716–10726.
[3 ]Grewe, J, Wachtler T., und Benda J. „A bottom-up approach to data annotation in neurophysiology“. Frontiers in Neuroinformatics 5 (2011): 16.
[4] Benda, J, Gollisch T., Machens C. , and Herz A., „From response to stimulus: adaptive sampling in sensory physiology“. Current Opinion in Neurobiology 17, Nr. 4 (August 2007): 430–436.
Keywords:
closed-loop,
Drosophila,
Electroretinogram,
Visiual System
Conference:
Bernstein Conference 2012, Munich, Germany, 12 Sep - 14 Sep, 2012.
Presentation Type:
Poster
Topic:
Data analysis, machine learning, neuroinformatics
Citation:
Garbers
C,
Schnaitmann
C,
Prech
S,
Tanimoto
H and
Wachtler
T
(2012). Novel method for closed-loop electroretinogram measurement of sensitivity in Drosophila.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference 2012.
doi: 10.3389/conf.fncom.2012.55.00265
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Received:
11 May 2012;
Published Online:
12 Sep 2012.
*
Correspondence:
Mr. Christian Garbers, Ludwig-Maximilians-Universität München, Department Biology II, Planegg-Martinsried, D-82152, Germany, garbers@biologie.uni-muenchen.de