First published online March 2, 2007
Journal of Experimental Biology 210, 1025-1035 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02717
Temperature dependent modulation of lobster neuromuscular properties by serotonin
Jonna L. Hamilton,
Claire R. Edwards,
Stephen R. Holt and
Mary Kate Worden*
Department of Neuroscience, University of Virginia Health Science
Center, Charlottesville, VA 22908-0230, USA
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 1. The amplitudes of EJPs and IJPs vary as a function of temperature. (A)
Intracellular recordings from a muscle fiber in which a single EJP and a
single IJP are elicited in each stimulus trial over the temperature range
2–18°C. Traces are averaged from ten trials at each temperature; the
resting potential (RP) recorded at each temperature is indicated above each
trace. In this experiment, the IJP reversed polarity at 6.0°C. (B)
Amplitude of EJPs as a function of temperature in nine muscle fibers. Data are
normalized to the value measured at 2°C; at this temperature EJP amplitude
in these fibers ranged from 1.4 to 12.9 mV. EJPs are depolarizing in polarity
over the entire temperature range. (C) Amplitude of IJPs as a function of
temperature in six muscle fibers. Data are normalized to values measured at
2°C; at this temperature IJP amplitude in these fibers ranged from
–0.1 mV to –5.2 mV. The broken line indicates the reversal of the
IJP polarity; data below the broken line represent IJPs of hyperpolarizing
polarity. (D) Muscle resting potential (mean ± s.e.m.) measured as a
function of temperature in 18 muscle fibers, including those for which data is
presented in B and C. (E) Input resistance of muscle fibers (mean ±
s.e.m.; N=11) measured in response to hyperpolarizing current pulses.
Values are normalized to those measured at 2°C.
|
|
View larger version (5K):
[in this window]
[in a new window]
|
Fig. 2. Electrical and contractile responses of muscle are temperature dependent.
Intracellular and tension recordings from dactyl opener muscle in response to
trains of stimuli delivered alternately to the inhibitory (OI) and excitatory
(OE) motoneurons. The timing of the stimulus trains (12 Hz for 700 ms for the
inhibitory motoneuron OI; 10 Hz for 500 ms for the excitatory motoneuron OE)
is indicated above the traces. Intracellular recordings of muscle membrane
potential are shown above the corresponding tension recordings, traces are
averaged from ten stimulus trials at the indicated temperatures. Muscle
resting potential was –56 mV at 2°C.
|
|
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 3. Serotonin (5-HT) increases the amplitude of EJPs and neurally evoked
contractions. (A) Representative recordings of EJPs (upper traces) and the
corresponding twitch contractions (lower traces) at 2°C are shown under
control conditions and 22 min after the addition of 50 nmol
l–1 serotonin. Each trace is the average of ten consecutive
recordings in response to a 200 ms train of 10 Hz stimulation. Serotonin
increased EJP size in this muscle fiber by approximately 30% and increased
twitch tension recorded from the entire muscle by 800%. (B) Serotonin elicits
a dose-dependent increase in EJP amplitude, with a threshold of approximately
1 nmol l–1 and maximal effects at 1 µmol
l–1. Results are expressed as the logarithm of the ratio of
EJP amplitude after application of serotonin with respect to its control
value. Symbols represent 13 measurements from 10 different preparations at a
temperature of 2°C. (C) Serotonin is most effective at potentiating small
EJPs. Symbols illustrate the magnitude of potentiation of EJPs by 50 nmol
l–1 serotonin recorded at bath temperatures of 16°C
(squares) and 2°C (triangles) expressed as the logarithm of the ratio of
EJP amplitude after application of serotonin with respect to its control
value. Each symbol represents a measurement from a different preparation.
Slopes of linear fits to data (not shown) are negative and significantly
different from zero (at 2°C slope=–0.03, P=0.002; at
16°C slope=–0.13, P=0.03). (D) Serotonin triggers muscle
action potentials. At 3°C in the presence of 50 nmol l–1
serotonin (broken trace) an action potential appeared superimposed on the
fourth EJP evoked by a 30 Hz, 600 ms stimulus train. The control recording at
the same temperature is shown as a solid trace.
|
|
View larger version (13K):
[in this window]
[in a new window]
|
Fig. 4. Serotonin (5-HT) potentiates both IJP amplitude and the size of neurally
evoked relaxations. (A) Intracellular recordings of IJPs (left) evoked at
2°C by a stimulus train (7 Hz, 700 ms) delivered to the inhibitory (OI)
motoneuron in the absence (control) and in the presence of 100 nmol
l–1 5-HT. 5-HT depolarized the resting potential of this
muscle fiber at 2°C from –66 mV to –60 mV. Corresponding
relaxations of muscle tension are shown at right. Both intracellular and
tension traces are averaged from five stimulus trials. (B) Plot of IJP
amplitude (squares) and neurally evoked relaxations (triangles) as a function
of temperature in the absence (open symbols) and presence (solid symbols) of
5-HT. Data in B are from the same experiment as in A. The reversal potential
of the IJPs in this experiment was 4.3°C under control conditions and
9°C in the presence of 5-HT. (C) Intracellular recording of IJPs from the
same muscle fiber at 6°C under control conditions (upper trace) and in the
presence of 5-HT; data are from the same experiment as in A and B. (D) Data
pooled from four experiments; symbols represent the amplitude of relaxations
evoked by stimulus trains delivered to the inhibitory (OI) motoneuron in the
absence (open symbols) and the presence (solid symbols) of 5-HT. At each
temperature N=4 except as follows: in control data N=3 at
10°C and N=1 at 12°C; in 5-HT data N=2 for 8°C,
10°C and 12°C. Asterisks indicate values that are significantly
different from controls (paired t-test, P<0.05).
|
|
View larger version (7K):
[in this window]
[in a new window]
|
Fig. 5. Temperature dependence of the muscle fiber resting potential in the
presence and absence of serotonin (5-HT). Symbols represent the change in
resting potential with respect to the value measured at 2°C measured in
the same eight muscle fibers as a function of temperature in the absence
(solid symbols) and presence (open symbols) of 5-HT. Data are normalized in
both cases to the values of the resting membrane potential recorded at
2°C. Addition of 5-HT (100 nmol l–1) at 2°C produced
a mean change in resting membrane potential of +4.75 mV; the data measured in
the presence of 5-HT is offset accordingly. Arrows indicate the temperatures
at which IJPs reverse polarity (Trev) under control
conditions (6.6°C) and in the presence of 5-HT (13.2°C). At each
temperature N=8 except as follows: for 10°C N=6, for
12°C N=4, for 14°C N=2.
|
|
View larger version (13K):
[in this window]
[in a new window]
|
Fig. 6. Modulation of neurally evoked contractions by 5-HT is temperature
dependent. (A) Neurally evoked contractions recorded under control conditions
(lower traces) and in the presence of 50 nmol l–1 5-HT (upper
traces) at the indicated temperatures. Each trace is the average of ten
consecutive recordings. (B) Temperature dependence of neurally evoked
contraction strength in muscle fibers (N=6) in the absence (open
symbols) and presence (closed symbols) of 5-HT (50 nmol l–1).
Control data are normalized relative to the average contraction amplitude
recorded at 2°C (error bars are not larger than the symbols); 5-HT data
are normalized relative to the potentiating effect of 5-HT on contraction
amplitude (an increase of 1112%) at 2°C in the same preparations. (C)
Potentiation of neurally evoked contractions by 50 nmol l–1
5-HT recorded at bath temperatures between 2°C and 22°C (N=5
muscle fibers at 20°C and 22°C, N=6 at all other
temperatures). Symbols illustrate the logarithm of the ratio of neurally
evoked contraction strength after application of 5-HT with respect to the
control value at the same temperature. Asterisks indicate values that are
significantly different from data recorded at 2°C (independent
t-test, P<0.05).
|
|
View larger version (12K):
[in this window]
[in a new window]
|
Fig. 7. Serotonin increases resting muscle tension most strongly at the coldest
temperatures. (A) Bath temperature recorded as a function of time illustrating
the change from 2°C to 22°C and back to 2°C before and during
application of 50 nmol l–1 5-HT (hatched bar). (B) Resting
muscle tension in the same preparation recorded at temperatures indicated in
A. (C) Muscle tension (mean ± s.e.m.) recorded at 2°C and 22°C
in the absence and presence (hatched bar) of 5-HT (50 nmol
l–1) in the same seven preparations. Values for P
(paired t-test) are indicated by horizontal brackets. The break in
the x-axis indicates the distinction between the first temperature
warming protocol and the second.
|
|
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 8. Schematic diagram illustrating the temperature dependence of physiology and
behavior in the lobster H. americanus. With the exception of the data
reported by Crossin et al. (Crossin et
al., 1998 ), the indicated temperatures are those reported for
lobsters acclimated to cold (<6°C) temperatures.
|
|
© The Company of Biologists Ltd 2007
