Recordings of skin potentials of the paddlefish evoked by a weak electrical stimulus. (A) Recording from a single electrosensory neuron in the brainstem. Vertical dashes in the signal represent action potentials of the neuron. The slow waves evoked by the stimulus (in C) are skin potentials that the electrode also picks up. Note that the large electrosensory action potential is completely suppressed during the slow wave. (B) A recording with a bipolar electrode at the skin surface outside the fish located at the base of the rostrum. Here, mainly oscillatory potentials are present with a latency of about 750 ms to the stimulus. (C) The stimulus is a 100 μV cm−1 pulse in the water surrounding the fish with a duration of 100 ms.
Recordings of skin potentials from 10 successive stimulations (top to bottom), each separated by 1 minute. (A) The pulse had a positive polarity. Spike potentials and slow waves can be evoked after the first four stimulus presentations, but later on, stimuli often fail to evoke a clear response. (B) Responses to a negative pulse. Also here, the delayed rapid oscillatory response is often missing.
Intracranial recordings of skin potentials evoked by electrical pulses with different durations (field strength 100 μV cm−1). Only pulses longer than 20 ms reliably evoked a response.
Differences in skin potentials as measured outside the skin and across the skin epithelium at different depths. A metal electrode was initially placed 100 μm above the skin and then advanced in 100 μm steps while stimulating with a stimulus of 100 ms duration and 100 μV cm−1 duration. The depth values given were relative to the skin surface with negative values representing positions above the skin. Above the skin, only slow oscillatory waves could be recorded. On the inside (third series), a slow negative signal was observed in addition.
(A) Recordings of the fast spike potential beginning at the tip of the rostrum (top trace) to a level just caudal to the tip of the gill cover in 1 cm steps. Traces are aligned to the stimulus onset (not shown). Stimulus was a 100 μV cm−1 pulse with 100 ms duration. (B) Plot of the delay of the first large negative peak of the spike potential as a function of the distance from the tip of the rostrum. The delay is relative to the delay of the response at the tip of the rostrum. Vertical scale bar in A equals 0.5 mV.
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