Remote Control of a Sea Slug
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The fine wire electrode technique [1] was adapted for Tritonia
studies. The lightness of the fine wire allows Tritonia to behave
freely in an aquarium while brain activity is being recorded.The
"brand" shaped tip of the fine wire was placed directly on the dry,
inner sheath above the Pd3 motor neuron, and a small drop of liquid
glue was used to insulate the exposed wire from the sea water. The
voltage difference between the "brand" and the reference electrode
was amplified and recorded on the video/data tape recorder. The
slug was allowed to recover from surgery in the behavioral arena
aquarium until it resumed normal crawling behavior.
Remote Control of a Sea Slug
Single Neuron Contribution to Turning while Crawling in the Marine
Slug Tritonia diomedeaRoger Redondo* & James A MurrayDepartment
of Biology, University of Central Arkansas, Conway, AR 72035
Tritonia diomedea crawls using its ciliated foot surface as the
sole means of propulsion. Turning while crawling involves the
raising of a small portion of the lateral foot margin ipsilateral
to the side of the turn. The cilia in the lifted area can no longer
contribute to propulsion, and this consequent asymmetry in thrust
turns the animal towards the lifted side. Pedal cell number 3
elicits the raising of the foot mid-anterior foot margin when
stimulated. The role of this cell during turning has been studied
in freely behaving slugs.
This research was done at the University of Central Arkansas and
the Friday Harbor Laboratories. Support was provided by the
University of Central Arkansas, the Arkansas Science and Technology
Authority, and a Libbie Hyman scholarship to RR. We also gratefully
acknowledge the assistance of Jessica Alexander, Jeff Blackwell,
Marty Erwin, Allan Roisen, Russell Wyeth, and the staff of the
Friday Harbor Laboratories.
Pedal 3 Stimulation is Sufficient to Elicit Turning
Pedal 3 Activity Correlates with Turning
Three video cameras were placed above and lateral to the slug such
that they could record the slugs position, orientation, and speed
onto the video/data tape [2,3]. Each video frame of the slug's
behavior was synchronized with the electrical activity from its
turning motor neurons.
Extracellular fine wire recordings show a single spike every time
the cell right underneath the wire fires an action potential [4].
The train of spikes from both neurons was quantified on computer
into spikes per second using the Spike2 data acquisition program
[5]. The synchronicity of spike activity and behavior allowed us to
study the role of Pedal 3 in the turning of the animal.
[9, 10] During stimulation trials, single squared pulses, at a
frequency of 4 Hz and 10 ms duration, were able to elicit turning
once the stimulus intensity reached 800mV. The absence of secondary
responses from the animal supports our single cell stimulation
theory. Furthermore, the turn is away from the source of flow
indicating that any sensory information about the direction of the
current has been overridden by our artificial stimulus.
Methods
Pedal 3 increases its firing activity during ipsilateral turns.
Figures 6, 7 & 8 show a turn to the left and a turn to the
right (left and right portions of the graphs, respectively). Right
Pedal 3 increases its frequency of firing during a right turn [6].
Similarly, Left Pedal 3 shows higher activity during a turn to the
left [7]. Superimposed cell activities show the synchronicity of
bursts of activity on both cells, and the faster rate of activity
of RPd3 with respect to LPd3 when turning towards the ipsilateral
side [8].
There is a positive correlation between the activity of Pedal cell
3 and the direction of turn taken by Tritonia.
Stimulation through Pedal cell 3 elicits an ipsilateral turn in
a freely crawling Tritonia.
Nerve recording to ensure single cell stimulation.Simultaneous fine
wire and intracellular to ensure largest spike belongs to closest
cell.Single cell killing studies: Dead Pd3 --> no rheotaxis
(turn into the source of flow)Study & stimulate Pd21
(responsible in part for the speed of crawling of the animal) using
fine wire.
Acknowledgements
Summary
Future Experiments
10
9
Introduction
Contact Information
Roger Redondo, Graduate Student:
[email protected]://faculty.uca.edu/~jmurray/murraylab.htm
Dr. James A. Murray, Assistant Professor:
[email protected]://www.uca.edu/biology/faculty/jmurray.htm
250 mV