Title:
Experimental Investigation of Magnetic and Electrical Stimulation in the Crayfish Giant Axon
Abstract:
This research tests whether a single-pulse magnetic or electrical stimulation can evoke an action potential (AP) in an isolated crayfish (Procambarus clarkii) axon. There are two working hypotheses:
- Electrical (extracellular) Stimulation- The induced electric field (E) produced by an electrical pulse would depolarize the axonal membrane sufficiently to trigger an AP. The specific objective was to determine the parameters necessary (electrical current, probe placement, axon position) and under which an electrically evoked AP can be detected, establishing practical threshold bounds for an unmyelinated invertebrate axon.
- Magnetic (intracellular) Stimulation- The induced electric field (E) produced by a rapidly changing coil current (dI/dt) would depolarize the axonal membrane sufficiently to trigger an action potential. The specific objective was to determine the parameter ranges (coil position, intensity, pulse width, axon position) under which a magnetically evoked AP can be detected, establishing practical threshold bounds for an unmyelinated invertebrate axon.
For both experiments, adult crayfish were prepared using established dissection protocols, with abdominal ganglia left in continuity and immersed in saline. For intracellular experiments, the ganglia were additionally desheathed. In the electrical stimulation experiments, electrical stimuli were applied at the ganglia, while action potentials were monitored using suction electrodes. In the magnetic stimulation experiments, the desheathed axon was probed with microelectrodes to record membrane potentials, and the single-pulse magnetic stimulation was delivered via a coil, while the axon was positioned in a chamber designed to maximize field gradients.
Despite systematic variation of coil position and stimulation intensity, no reproducible action potential was recorded in response to magnetic pulses. Similarly, no reproducible action potential was recorded in response to electrical pulses. These results demonstrate that under the tested conditions, the stimulation was insufficient to reach the activation threshold. The crayfish axon is unmyelinated across the recording region. The absence of myelin means that capacitive charge leaks continuously along the membrane. This reduces the effectiveness of any transient field. Consequently, the unmyelinated crayfish axon represents a challenging target for excitation as it requires a higher activation threshold. The necessary magnetic and electrical stimuli were not possible within the scope of these experiments.
Research Advisor:
Prof. Sergey Makaroff
ECE Department, WPI
Research Committee:
Prof. Reinhold Ludwig
ECE Department, WPI
Prof. Greg Noetscher
ECE Department, WPI
Dr. William Wartman
ECE Department, WPI