Spike Potentials produced by the Sea Lamprey (Petromyzon marinus) in the Water surrounding the Head Region


UNDER the auspices of the Fisheries Research Board of Canada an investigation was started recently in this laboratory on hearing in the sea lamprey. During preliminary observations, adult Petromyzon marinus were placed in rigid ‘Lucite’ cylinders of 1½ in. inner diameter. A row of silver electrodes had been placed in the wall of the tube at 1-in. intervals along a straight longitudinal line. Each of the electrodes could be connected individually with a d.c.-fed pre-amplifier. The last electrode in the row, located beyond the tail of the animal, served as reference electrode. The tube, filled with fresh water and containing the animal, was kept in a Faraday cage together with the pre-amplifier. The output of the amplifier was connected with a cathode ray oscilloscope. In the water surrounding the head region spike potentials were recorded from electrodes 15–20 mm. away from the animal's surface. Fig. 1 represents a recording from an electrode located immediately above the left eye of the animal. The triphasic spike has a duration of about 20 m.sec. and a potential of 200 µV.; the positive third phase has a potential of 30 µV. and lasts about 15 m.sec. Successive recordings from electrodes headwards or tailwards demonstrated that the highest potentials in the water were towards the anterior extremity of the animal, that is, surrounding the region of the head anterior to the eyes. The values of the potentials decreased rapidly posteriorly to the eyes and no spikes could be recorded from electrodes beyond a distance of 2–3 in. from the eyes towards the tail of the animal. The electrical field was therefore confined to the anterior end of the body.

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