Functioning of identified snail neurones in electric fields

In both silent and spontaneously active neurones of the snail Helix lucorum, depolarization and spikes were elicited by low-frequency (0.1 Hz) sinusoidal currents applied to the bath solution. Threshold voltage gradients had a range of 1-10 V m-1, which is less than gradients in the nervous tissue during synchronous activation of the neurones. It is shown that the same neurone can generate spikes in response to opposite directions of polarizing currents. Thresholds of spontaneously active neurones to extracellular currents were significantly lower than thresholds of silent cells. A simple quantitative method for evaluation of the transmembrane voltage drop evoked by an electric field is presented. The role of neuronal branches in the response was studied by electrophysiological and morphological methods.