Remote Control of a Sea Slug

1. Single Neuron Contribution to Turning while Crawling in the Marine Slug Tritonia diomedea Roger Redondo* & James A Murray Department of Biology, University of Central Arkansas, Conway, AR 72035 Introduction Summary Pedal 3 Activity Correlates with Turning 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. • 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. 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]. Future Experiments • 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. • 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. Pedal 3 Stimulation is Sufficient to Elicit Turning 9 250 mV Acknowledgements 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. 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. 10 Contact Information Roger Redondo, Graduate Student: rogerrp@yahoo.com http://faculty.uca.edu/~jmurray/murraylab.htm Dr. James A. Murray, Assistant Professor: jmurray@mail.uca.edu http://www.uca.edu/biology/faculty/jmurray.htm • [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. 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. Remote Control of a Sea Slug