Abstract

Maximal electroshock seizures were induced in adult male albino mice with current intensities of 12.5, 25, 50, 200, and 400 mA (60-cycle a.c., 0.2-second duration, corneal electrodes), and the following variables measured: seizure pattern and duration, time for 50 per cent of animals to recover the ability to exhibit a second tonic-clonic seizure after an initial seizure (RT⁵⁰), and anticonvulsant potency of phenobarbital. The results were as follows:

1. The mean duration of hindleg tonic flexion increased as the stimulus intensity was increased. The mean duration of hindleg tonic extension was significantly longer only in seizures evoked by a stimulus intensity of 400 mA. The flexion/extension ratio progressively decreased as the stimulus intensity was increased. The mean duration of terminal clonus did not vary with the intensity of the stimulus. The mean total duration of seizures elicited with 12.5 and 400 mA of current was significantly longer than those evoked with the other stimulus intensities.

2 A statistically significant increase in RT⁵⁰ was observed as the intensity of the stimulus employed to evoke the initial seizure was increased. There was a direct linear relation between log RT⁵⁰ and log stimulus intensity.

3. Variations in current strength from 50 to 800 per cent of the standard stimulus failed to effect a significant change in phenobarbital anticonvulsant potency.

It is concluded that increased stimulus intensity increases seizure severity, and that hindleg tonic-flexion duration and recovery time are more sensitive measures of seizure severity than is phenobarbital anticonvulsant potency; the latter, as determined by the conventional test which is based on the prevention of the hindleg tonic-extensor component of the maximal electroshock seizure, is relatively independent of stimulus intensity.