Electroshock afterdischarges are related to neuronal oscillability: neuronal models of Aplysia

Identifiable giant neurons of Aplysia explored intracellularly behave differently at the offset of an intracellular electroshock (IES) or after a synaptic 'tetanization', according to their functional type: neurons of the stable type depolarize and fire at the offset of the IES, anodal or cathodal, thus eliciting an afterdischarge (AD). The threshold of this AD is lowered if the neuron is destabilized, i.e. converted from the stable to an oscillatory type (for instance by decalcification). Neurons normally of the tonic type are more sensitive to an IES, eliciting a longer afterdischarge than the stable neurons. Extracellular electroshock (EES) anodal or cathodal, applied directly on desheathed somata of Helix give long-lasting afterdischarges at the offset. In addition, EES stimulating presynaptic terminals or axons leads to a high frequency synaptic input on remote neurons. At the offset of this input either prolonged synaptic afterdischarges or postsynaptic rebounds of the membrane potential sustaining bursts of decreasing amplitude denote apparent oscillatory properties of the synaptically activated neuron. Finally, any conversion by convulsants of tonic neurons to oscillators highly facilitates the elicitation of afterdischarges of axons simultaneous to paroxysmal depolarization shifts of the homologous somata. These results indicate that afterdischarge elicitation is highly facilitated (low threshold) in normal oscillatory neurons and/or chemically destabilized neurons.