The effects of pentylenetetrazol on molluscan neurons. I. Intracellular recording and stimulation.

The effects of the convulsant drug pentylenetetrazol (PTZ) were studied in neurons from isolated ganglia of the nudibranch molluscs, Archidoris montereyensis and Anisodoris nobilis, using conventional techniques of intracellular recording and constant current stimulation. PTZ was selected because it causes changes in the intracellularly recorded responses similar to the depolarization shifts recorded in mammalian epileptic neurons. When perfusate containing 120-140 mM PTZ is introduced, the intracellular recording is characterized by an initial silent period followed by small oscillations in membrane potential and irregular firing of spikes. Within 5-15 min, bursts of 2-3 spikes occurred followed by the appearance of episodic prolonged depolarizations with superimposed high-frequency spikes. In the presence of PTZ the prolonged depolarizations were evoked by intracellular stimulation and at the termination of conditioning hyperpolarizations. The prolonged depolarizations were also recorded in neurons isolated from all synpatic input by axonal ligation. Prolonged depolarizations showed threshold behavior since they can be terminated early by an intracellularly applied hyperpolarizing current.