66 lines
4.4 KiB
TeX
66 lines
4.4 KiB
TeX
\subsection*{Electrophysiology}
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We recorded electrophysiological data from X cells from Y different fish.
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\textit{Surgery}. Twenty-two E. virescens (10 to 21 cm) were used for
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single-unit recordings. Recordings of electroreceptors were made
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from the anterior part of the lateral line nerve.
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Fish were initially anesthetized with 150 mg/l MS-222 (PharmaQ,
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Fordingbridge, UK) until gill movements ceased and were then
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respirated with a constant flow of water through a mouth tube,
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containing 120 mg/l MS-222 during the surgery to sustain anesthesia.
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The lateral line nerve was exposed dorsal to the operculum. Fish were
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fixed in the setup with a plastic rod glued to the exposed skull bone.
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The wounds were locally anesthetized with Lidocainehydrochloride
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2\% (bela-pharm, Vechta, Germany) before the nerve was exposed.
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Local anesthesia was renewed every 2 h by careful application of
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Lidocaine to the skin surrounding the wound.
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After surgery, fish were immobilized with 0.05 ml 5 mg/ml tubocurarine (Sigma-Aldrich, Steinheim, Germany) injected into the trunk
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muscles.
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\sout{Since tubocurarine suppresses all muscular activity, it also
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suppresses the activity of the electrocytes of the electric organ and thus
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strongly reduces the EOD of the fish. We therefore mimicked the EOD
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by a sinusoidal signal provided by a sine-wave generator (Hameg HMF
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2525; Hameg Instruments, Mainhausen, Germany) via silver electrodes
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in the mouth tube and at the tail. The amplitude and frequency of the
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artificial field were adjusted to the fish’s own field as measured before
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surgery.} After surgery, fish were transferred into the recording tank of the
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setup filled with water from the fish’s housing tank not containing
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MS-222. Respiration was continued without anesthesia. The animals
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were submerged into the water so that the exposed nerve was just above
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the water surface. Electroreceptors located on the parts above water
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surface did not respond to the stimulus and were excluded from analysis.
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Water temperature was kept at 26°C.\footnote{From St\"ockl et al. 2014}
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\textit{Recording. }Action potentials from electroreceptor afferents were
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recorded intracellularly with sharp borosilicate microelectrodes
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(GB150F-8P; Science Products, Hofheim, Germany), pulled to a resistance between 20 and 100 M and filled with a 1 M KCl solution.
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Electrodes were positioned by microdrives (Luigs-Neumann, Ratingen,
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Germany). As a reference, glass microelectrodes were used. They were
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placed in the tissue surrounding the nerve, adjusted to the isopotential line
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of the recording electrode. The potential between the micropipette and the
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reference electrode was amplified (SEC-05X; npi electronic) and lowpass filtered at 10 kHz. Signals were digitized by a data acquisition board
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(PCI-6229; National Instruments) at a sampling rate of 20 kHz. Spikes
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were detected and identified online based on the peak-detection algorithm
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proposed by Todd and Andrews (1999).
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The EOD of the fish was measured between the head and tail via
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two carbon rod electrodes (11 cm long, 8-mm diameter). The potential
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at the skin of the fish was recorded by a pair of silver wires, spaced
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1 cm apart, which were placed orthogonal to the side of the fish at
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two-thirds body length. The residual EOD potentials were recorded
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and monitored with a pair of silver wire electrodes placed in a piece
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of tube that was put over the tip of the tail. These EOD voltages were
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amplified by a factor of 1,000 and band-pass filtered between 3 Hz and
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1.5 kHz (DPA-2FXM; npi electronics).
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Stimuli were attenuated (ATN-01M; npi electronics), isolated from
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ground (ISO-02V; npi electronics), and delivered by two carbon rod
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electrodes (30-cm length, 8-mm diameter) placed on either side of the
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fish parallel to its longitudinal axis. Stimuli were calibrated to evoke
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defined AM measured close to the fish. Spike and EOD detection,
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stimulus generation and attenuation, as well as preanalysis of the
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data were performed online during the experiment within the
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RELACS software version 0.9.7 using the efish plugin-set (by J.
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Benda: http://www.relacs.net).\footnote{From St\"ockl et al. 2014}
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\textit{Stimulation.} White noise stimuli with a cutoff frequency of 300{\hertz} defined an AM of the fish's signal. The stimulus was combined with the fish's own EOD in a way that the desired AM could be measured near the fish. Amplitude of the AM was 10\% (?) of the amplitude of the EOD. Stimulus duration was between 2s and 10s, with a time resolution of X.
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