First published online June 11, 2007
Journal of Experimental Biology 210, 2199-2211 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.002865
Behavioral context-dependent modulation of descending statocyst pathways during free walking, as revealed by optical telemetry in crayfish
N. Hama1,*,
Y. Tsuchida2 and
M. Takahata1
1 Animal Behavior and Intelligence, Division of Biological Science, Graduate
School of Science, Hokkaido University, Sapporo 060-0810, Japan
2 Research Institute for Electronic Science, Hokkaido University, Sapporo
060-0810, Japan
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Fig. 1. Experimental set-up. (A) Arrangement of the telemetry and video-recording
systems. The crayfish was placed in an experimental aquarium filled with water
to a depth of 15 cm. The floor was tilted by 10°. Four PIN-photodiodes
(PINPDs) as receivers were placed at the corners of a square of 30 cmx30
cm. An LED was driven by synchronous signals that were simultaneously fed,
together with nerve and EMG signals, to a DAT recorder. Due to the optical
signal decay along the distance from the transmitter, the recording was
reliable only in a limited area. The area illustrated in dark blue indicates
the area in which the telemetric transmission was secure. The light blue
indicates water in the aquarium. (B) The angular coordinate adopted in the
present study to describe the direction of animal body orientation. The head
direction and behavior of crayfish were video-recorded from above. (C) The
optical transmitter mounted on the animal. Wire electrodes for
electromyographic (EMG) recording from the mero-carpopodite flexor muscle and
the chronic electrode for extracellular recording from the circumesophageal
commissure were connected to the dual-channel transmitter. (D) Schematic
drawing of the chronic electrode for extracellular recording from the
circumesophageal commissure. Wire connection from the electrode to the
transmitter is shown by broken lines. The commissure was hooked up lightly by
the electrode to secure the recording during free movements. Two broken ovals
are lithium cells for the transmitter. They were omitted from the illustration
in C for the sake of clarity. IRLED; infrared LED.
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Fig. 2. Unit activities identified from extracellular recordings of the whole
circumesophageal commissure using discriminating software. (A) Raw recording
data during walking (upper trace); these data are partially expanded in the
lower trace. Four units could be discriminated in this example, as indicated
by four different symbols. (B) Activity of each unit during forward walking
(i) and backward walking (ii). The histograms were based on 1 s time bins.
Units 3a and 3b showed almost the same activity during forward and backward
walking. Units 3c and 3d showed higher activities during backward walking than
during forward walking. The vertical broken lines indicate the time of onset
of walking behavior. The thick gray bar at the bottom indicates the expanded
part of the data shown in A. The insets on the right (iii) show
superimposition of each unit. They are expanded in the time scale as indicated
but are the same size in the voltage scale as in A except that unit 3a was
reduced to half of A in the voltage scale.
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Fig. 3. Responses of interneuron C1 to body and substratum tilting. (Ai)
Body tilting by 90° in the air. The top trace shows the spike activity
recorded extracellularly from the circumesophageal commissure (CC). The spike
activity of interneuron C1 was isolated electronically from the
commissural recording and is shown in the middle trace. The bottom trace
monitors animal body tilting, the upward and downward deflection indicating
ipsilateral-side-down (ISD) and contralateral-side-down (CSD) tilting, in
which the side of commissural recording was lowered and lifted, respectively.
(Aii) Statistical comparison of interneuron activities between horizontal,
ipsilaterally tilted and contralaterally tilted positions
(*P<0.05; ANOVA). The inset shows superimposition of
electronically isolated spikes in Ai. (Bi) Substratum tilting by 10°. The
animal was standing on the tilted substratum. Since the animal was free to
evoke postural reflexes, the exact angle of body tilt on the tilted substratum
was unknown. The recording for each positioning was made intermittently
whenever the freely behaving animal met the behavioral and orientation
requirements. (Bii) Statistical comparison of the interneuron activities
(*P<0.05; ANOVA).
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Fig. 4. Effects of leg and abdominal movements on interneuron C1
activity. (A) Body tilting in the contralateral-side-down direction (i)
without a leg substratum when the animal was at rest and (ii) with actively
moving legs. The animal body was kept tilted during the recording shown in i
and ii. In each part, the top trace monitors muscle activity whereas the
bottom trace monitors interneuron C1 activity. (B) An exceptional
case in which the interneuron activity was affected by leg movements in the
air. The spike activity during maintained tilt of the resting animal (i) was
significantly enhanced when the animal actively moved its walking legs (ii).
(C) Effects of abdominal posture movements on interneuron activity. Upward and
downward arrows indicate the onset time of abdominal extension and flexion
movements, respectively. No noticeable change was observed in interneuron
activity during these movements.
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Fig. 5. Interneuron C1 activity during free walking. (Ai) Recordings
from an animal that spontaneously initiated walking (vertical broken line) on
the horizontal floor of the aquarium. The top trace shows the extracellular
recording from the circumesophageal commissure (CC); the second trace shows
the EMG recording from the mero-carpopodite flexor muscle of the right second
leg; the third trace shows interneuron C1 activity, which is also
represented in the form of a frequency histogram with the time bin of 1 s
underneath. (ii) Superimposition of interneuron spikes discriminated from the
commissural recording. For clarity, the superimposed record is enlarged in
both the time and voltage scale. The former scale is provided in the figure
while the latter factor was 3.0 relative to the raw data. (B) Statistical
comparison of interneuron C1 spike activity between the resting and
walking conditions (*P<0.05; Mann–Whitney U-test).
(C) Interneuron activity when the animal walked on the tilted floor in
different directions. The angular coordinate is shown in
Fig. 1B. When the animal walked
in 0° and 180° directions, the floor was bilaterally symmetrical for
the animal body. In the direction of 90° and –90°, the animal
body was tilted in the contralateral-side-down and ipsilateral-side-down
directions, respectively. The gray bars depict the animal walking on the
substratum tilted in the contralateral-side-down direction.
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Fig. 6. Interneuron C1 spike activity dependent on the abdominal posture
movements during free walking. (A) Tracing of two bouts of walking on the
tilted floor. The body position and head orientation are plotted at 1 s
intervals. The filled circles indicate the head while the straight lines
indicate the longitudinal body axis of the animal. In the first bout of
walking, the animal walked forwards with the abdomen extended (Ab. Ex. FW).
The animal then turned left and started the second walking in the backward
direction with the abdomen flexed (Ab. Fl. BW). Smooth-line arrows in the
figure indicate approximate displacement of the animal. (B) Spike activity of
interneuron C1 during the walking shown in A. Represented in the
form of a frequency histogram with the time bin of 1 s, the record shows that
the interneuron activity was enhanced when the animal started abdominal
flexion (indicated by a vertical line). The crayfish behavior is shown in the
top bar: P, pause; Ab. Ex. FW, forward walk with abdomen extended; Ab. Fl. BW,
backward walk with abdomen flexed. Head orientation is monitored in the top
trace. (C) Spike activities of interneuron C1 in different
orientation angles. Filled and open bars indicate the spike activity during
abdominal flexion and extension, respectively.
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Fig. 7. Effects of abdominal posture on descending interneurons other than
interneuron C1. (Ai) Two statocyst-driven descending units in the
circumesophageal commissure. The original recording is shown at the top (CC),
and two unit activities (A and B) discriminated from the record are shown in
the second and third traces. The bottom trace monitors body tilt angle. Unit A
responded directionally to ipsilateral-side-down tilting (ISD) whereas unit B
responded to contralateral-side-down tilting (CSD). (ii) Superimposition of
interneuron spikes from the two isolated units. For clarity, the superimposed
records are enlarged in both the time and voltage scale. The former scale is
provided in the figure while the latter factor was 5.0 relative to the raw
data for both units. (B) Spike activities during walking in different
orientation angles with the abdomen extended (open bars) and flexed (filled
bars). Unit A (i) showed no directional responses when the animal extended or
flexed its abdomen whereas unit B (ii) could represent directional information
when the animal extended its abdomen. Unit B showed no directional responses
during abdominal flexion.
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© The Company of Biologists Ltd 2007
