Modulation of the endogenous electrical activity of the bursting neuron in the snail Helix pomatia—I. The generator of the slow rhythms

Abstract

Electrical activity of the bursting neuron RPal of the snail Helix pomatia was found to be subjected to periodic modulation with an interval of about 100s. The modulation was produced by waves of membrane potential the amplitude of which could change and the bursting activity could be even transformed into the beating one. Clamping the membrane potential in this neuron revealed a periodic slow inward current which appears to cause the modulation of the neuron's electrical activity. The exogenous nature of the generator of the slow inward current in the neuron RPa1 and in other studied neurons was demonstrated. Decrease in the extracellular calcium ion concentration from 10 to 0.4 mM, with a simultaneous increase of magnesium ion concentration from 4 to 14 mM, caused no marked changes in the periodicity of the slow inward current. Decrease in the extracellular sodium ion concentration from 100 to 50 mM increased the interval between the phases of slow inward current and finally led to the complete disappearance of the current. It is suggested that a neurosecretory interneuronal communication exists in the snail brain which has a different mechanism from conventional synaptic transmission.