Leech Neurophysiology Lab

Purpose: The purpose of this lab was to attempt to identify the different types of cells that are located within the Ganglion of a leech.


Hypothesis: I predict that the different types of cells will have a larger reaction when stimulated by a harder object like the probe or forceps while having little reaction to a feather.


Materials: 

• Feather - Used to give the leech skin a very gentle touch stimulation.
• Probe - A blunt metal rod used to lift tissue, and to push the skin as a stimulus.
• Forceps - Used for very fine manipulations.
• Scissors - Angled dissecting scissors, used to cut the body wall open.
• Pins - Used for pinning tissue to a dissecting dish or board.
• Scalpel - For microsurgery, used to make incisions in the leech.
• Dissection Tray - The tray that the leech was pinned to.
• Leech Tank - Used to keep the leeches in a natural like environment.
• 20% Ethanol - Used to anesthetize the leech, more humane, it stops them from moving.
• Leech Tongs - Blunt tips so that the leech will not be harmed from picking it up.
• Dissection Microscope - Specifically designed for dissection and other micro-manipulations.
• Micro-manipulator - A device used to position the leech with sub-micrometer precision
• Oscilloscope - A sophisticated voltmeter.
• Leech - Medical leeches, 15-20cm long, 1-2cm wide

Procedure: First thing we had to do in this lab was to catch a leech from the tank and then anesthetize it and place it on the tray. Then we pinned it down, cut it down the middle, used forceps to tear the skin apart and then pinned the flaps to the tray. We then had to remove the innards with a probe so we could find the nerve cord which is encased in the ventral sinus. Then cut a window out of the ganglion under the dissection microscope, then cut a parallel section of the skin out and did the same with an ultra fine scalpel. Then used the micro-manipulator to stimulate the ganglion. Injected dye solutions into different spots and then used a UV switch to see where the dye had spread to. Then used an atlas to determine what type of cell we had stimulated.


Results: The results turned out pretty good overall. The atlas really helped to determine the types of cells we were probing, but some of them I still got wrong. The lab helped me understand the different types of cells a bit better.


Conclusions: The chart below shows that I was actually very wrong with my hypothesis. The 5 different types of cells found in the Ganglion all react differently to different types of stimulation.