University of Oulu

Rusanen, J., Frolov, R., Weckström, M., Kinoshita, M., Arikawa, K. (2018) Non-linear amplification of graded voltage signals in the first-order visual interneurons of the butterflyPapilio xuthus. Journal of Experimental Biology, 221 (12), jeb179085. doi:10.1242/jeb.179085

Non-linear amplification of graded voltage signals in the first-order visual interneurons of the butterfly Papilio xuthus

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Author: Rusanen, Juha1; Frolov, Roman1; Weckström, Matti1;
Organizations: 1Nano and Molecular Materials Research Unit, Faculty of Science, University of Oulu, PO Box 3000, Oulu 90014, Finland
2Laboratory of Neuroethology, Sokendai (The Graduate University for Advanced Studies), Hayama, Kanagawa 240-0193, Japan
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.2 MB)
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Language: English
Published: Company of Biologists, 2018
Publish Date: 2019-06-22


Lamina monopolar cells (LMCs) are the first-order visual interneurons of insects and crustacea, primarily involved in achromatic vision. Here, we investigated morphological and electrophysiological properties of LMCs in the butterfly Papilio xuthus. Using intracellular recording coupled with dye injection, we found two types of LMCs. Cells with roundish terminals near the distal surface of the medulla demonstrating no or small depolarizing spikes were classified as L1/2. Cells with elongated terminals deep in the medulla that showed prominent spiking were classified as L3/4. The majority of LMCs of both types had broad spectral sensitivities, peaking between 480 and 570 nm. Depending on the experimental conditions, spikes varied from small to action potential-like events, with their amplitudes and rates decreasing as stimulus brightness increased. When the eye was stimulated with naturalistic contrast-modulated time series, spikes were reliably triggered by high-contrast components of the stimulus. Spike-triggered average functions showed that spikes emphasize rapid membrane depolarizations. Our results suggest that spikes are mediated by voltage-activated Na+ channels, which are mainly inactivated at rest. Strong local minima in the coherence functions of spiking LMCs indicate that the depolarizing conductance contributes to the amplification of graded responses even when detectable spikes are not evoked. We propose that the information transfer strategies of spiking LMCs change with light intensity. In dim light, both graded voltage signals and large spikes are used together without mutual interference, as a result of separate transmission bandwidths. In bright light, signals are non-linearly amplified by the depolarizing conductance in the absence of detectable spikes.

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Series: Journal of experimental biology
ISSN: 0022-0949
ISSN-E: 1477-9145
ISSN-L: 0022-0949
Volume: 221
Article number: jeb179085
DOI: 10.1242/jeb.179085
Type of Publication: A1 Journal article – refereed
Field of Science: 3112 Neurosciences
Copyright information: © 2017 The Authors. Published by The Company of Biologists Ltd.