OSCILLATIONS OF THE TRANSEPITHELIAL POTENTIAL OF MOTH OLFACTORY SENSILLA ARE INFLUENCED BY OCTOPAMINE AND SEROTONIN
JAN DOLZER1,2,
STEFFI KRANNICH1,
KARIN FISCHER2 and
MONIKA STENGL1,2,*
1
Biologie, Tierphysiologie,
Philipps-Universität Marburg,
Karl-von-Frisch-Straße, D-35032 Marburg, Germany
2
Institut für Zoologie,
Universität Regensburg, D-93040 Regensburg,
Germany
*
Author for correspondence at address 1 (e-mail:
stengl{at}mailer.uni-marburg.de
)
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Fig. 5. (A) Action potentials recorded in sweeps of 12.75 ms duration. The initial
2.5 ms of each sweep were defined as baseline and used to measure the
transepithelial potential. The baseline was then adjusted to 0 mV. One large
(red line) and one small (blue line) action potential are highlighted. The
peak-to-peak (p-p) amplitudes of each action potential occurring over a 10 min
period were measured and plotted versus time (B). The amplitude
reduction during bursts then became obvious (arrowheads). The massive bursting
activity of the cell firing the small action potentials (solid arrowhead)
gives rise to a third peak when the data are presented as an amplitude
histogram (C), generating a false third action potential class (arrowhead).
Both types of plot were analyzed to determine the threshold for action
potential sorting (dashed lines).
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Fig. 4. (A,B) Spontaneous action potentials in the two olfactory receptor neurons
(ORNs) in a trichoid sensillum, distinguishable by their amplitudes. The three
parts in A are one continuous sequence. The action potentials of neither class
were randomly distributed, but (both) exhibited bursting activity. Bursts of
large action potentials are marked with filled circles, bursts of small action
potentials with open circles. The indicated burst (star) is shown on an
enlarged time scale in B. (C) A burst of large action potentials from a
different recording, illustrating the reduction in amplitude of the action
potentials. (D) Action potential bursts were also recorded with tungsten
electrodes placed near the hair base. The three parts of D are one continuous
trace, highpass-filtered at 5 Hz.
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Fig. 1. Fifteen hours of a recording of action potentials and the transepithelial
potential (TEP) of a trichoid sensillum with respect to the flight activity of
the moth. The recording starts approximately 50 h after the beginning of the
tip recording. The highpass-filtered signal (AC) reveals the action potentials
superimposed on the slow fluctuations of the TEP, illustrating that there was
no trend in the action potential activity. The time course of the TEP
exhibited regular oscillations for periods of up to several hours, termed
`oscillatory intervals'. These were interrupted by shorter periods,
`non-oscillatory intervals', during which the TEP fluctuated less regularly or
remained constant. Flight activity, recorded by a piezo-electric sensor at the
thorax, was restricted to non-oscillatory intervals.
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Fig. 3. (A—D) The time course of the transepithelial potential (TEP) during
injection of 50 nmol of serotonin. The sections indicated in A are shown on an
enlarged time scale in B—D. The TEP oscillation before drug injection
was asymmetrical, exhibiting a shoulder (arrowhead) after the positive peak
(B). After the injection, the oscillation was transiently suppressed and then
gradually recovered to approximately two-thirds of the original peak-to-peak
amplitude. After recovery, the oscillation was more regular than before, and
the shoulder was absent (C). Five hours after the injection, the peak-to-peak
amplitude had fully recovered, but the shoulder was not as prominent as before
(D). The animal exhibited flight activity only transiently immediately after
the drug injection.
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Fig. 2. (A-D) Recordings from four different animals showing the transepithelial
potential (TEP) and flight activity during injections of octopamine. (A) After
a delay of 1-2 min, the TEP oscillation was abolished by an injection of 1500
nmol of octopamine. Even after 15 h, the peak-to-peak amplitude had not
recovered (after the axis break). During the gaps, current step protocols and
resistance measurements (not shown) were performed. (B) While a control
injection of haemolymph Ringer only slightly and transiently reduced the
amplitude of the TEP oscillations, 150 nmol of octopamine almost completely
suppressed it. At 113 min, the animal exhibited flight activity, marking the
beginning of a non-oscillatory interval of approximately 2 h (not shown),
after which the oscillation reappeared. (C) After an injection of 20 nmol of
octopamine, the amplitude of the oscillation was reduced, but the time course
of the TEP remained periodic. Over the course of several hours after the
injection, the oscillation gradually regained its original amplitude and
regularity. (D) The effect of an injection of 2 nmol of octopamine into an
oscillation with a complex waveform could not reliably be distinguished from
the effects of control injections. Note the two non-oscillatory intervals
without TEP oscillations (12-30 min, 112-138 min) during which flight activity
was recorded.
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Fig. 7. No variable of the action potential (AP) activity correlated with
octopamine-dependent modulation of the transepithelial potential (TEP). (A)
Haemolymph Ringer (control) injection only slightly reduced and phase-shifted
the TEP oscillation for less than 20 min, while injection of 150 nmol of
octopamine caused a long-term depression of TEP oscillations. Flight activity
marked the beginning of a non-oscillatory interval. The frequency of both
action potential classes was unaffected by control or octopamine injections.
(B) None of the evaluated variables of the action potential activity was
affected by the injections. The first bin after the control injection (filled
circle) is only 5.2 min long.
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Fig. 6. (A,B) Action potential variables during oscillatory and non-oscillatory
intervals of the transepithelial potential (TEP). (A) The upper panel shows
the time course of the TEP and flight activity, while the lower panels
illustrate the action potential activity of the small and large action
potentials (APs), evaluated in bins of 10 s. Periods of elevated action
potential activity and quiescent periods occurred independently of the TEP and
of flight activity, during oscillatory as well as during non-oscillatory
intervals. (B) No correlation between the phase of the TEP oscillations and
any evaluated variable of the action potential activity was found. All
variables were analyzed in bins of 10 min and plotted on the same time axis as
in A. The frequency of the small action potentials was more variable than that
of the large ones (Table 3).
The percentage of action potentials that were members of bursts fluctuated
randomly between <25 and >75 %. Similarly, the mean number of action
potentials in each burst and the coefficient of variation (CV) did not exhibit
any correlation with the time course of the TEP. The dashed line marks a CV of
1, which would indicate a random distribution of the action potentials.
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Fig. 8. (A,B) Neither of the two action potential (AP) classes was significantly
influenced by amine injections. The frequencies of small and large action
potentials were evaluated for segments 10 min in duration within 30 min before
( before) and after (after) drug injections, and
the normalized frequency after/before was
computed. For comparison, data segments of 10 min, separated by 40-50 min, but
without any injection, were analyzed the same way. One-way analysis of
variance (ANOVA) did not reveal significant differences between any dose of
the injected drugs, the control (injected with haemolymph Ringer) and the
non-injected state. Values are medians + S.E.M. Values of N given in
A also apply to B. 5-HT, serotonin; OA, octopamine; HLR, haemolymph
Ringer.
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Fig. 9. Significantly more current was necessary to elicit small action potentials
than large action potentials. (A) Action potentials elicited by a series of 50
ms current steps, increasing by +25 pA from bottom to top. Passive electrical
responses were compensated by adding the responses of two pre-pulses of
opposite polarity and half the amplitude to each sweep. The large action
potentials (filled arrowheads) required a current of 175 pA, while the small
action potentials (open arrowheads) were first elicited by a 225 pA step. The
action potentials marked with open circles were considered to be spontaneous,
since either no action potential was present in the next sweep or the action
potential occurred outside the current step. (B) The small action potentials
required significantly more current (244 pA) than the large ones (208 pA).
Values are means + S.E.M., N=123 sets of five step protocols without
drug injection. The asterisk indicates a significant difference from the
control (P<0.01, Student's t-test). For both classes of
action potential, no significant changes were detected after the injection of
any dose of octopamine or serotonin (not shown).
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Fig. 10. Octopamine reduced the resistance of the preparation in a dose-dependent
manner. (A) For resistance measurements, 10 subsequent pulses of negative
current were applied. When compared with the averaged voltage response
( V) before drug injection (left), an injection of 150nmol of
octopamine decreased the response (right). (B) The normalized resistance
Rafter/Rbefore was computed. While
control injections of haemolymph Ringer (HLR) did not alter the resistance of
the preparation, octopamine (OA) reduced it in a dose-dependent manner.
Serotonin (5-HT), however, had no effect. Values are means + S.E.M. The
asterisk indicates a significant difference from the control
(P<0.02, Student's t-test).
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© The Company of Biologists Ltd 2001
