Abnormal plastic phenomena of sensory-precipitated epilepsy in the mutant El mouse

The processes of development of seizures of the El mouse, an inbred mutant strain susceptible to epilepsy, were investigated by long-term clinical observations and EEG recordings. The phenomena of extinction, reinforcement, and an aftereffect of the antecedent occurrence of seizures were observed. Seizures of El mice were elicited by repetition of natural sensory stimulation, which consisted of observation and tossing procedures. The seizure thresholds were lowered with a repetition of stimuli, and the incidence of seizures became higher, attaining 100%. Clinical manifestations started with abortive forms several weeks after the mice were initially exposed to stimulation, and concluded with typical general convulsions and wild running. Paroxysmal discharges appeared in the EEG as isolated spikes, first from restricted parietal areas; subsequently spike and wave complexes were extedded over wide areas of the brain. Even during the interictal period isolated spikes sometimes could be seen in the EEGs of the El mice most susceptible to seizures. After a long period without stimulation, the thresholds were raised, or extinction of seizures was observed in mice with fully developed seizures. Reinforcement stimulation was necessary for seizures of El mice to occur constantly. During recovery of the occurrence of seizures, their incidence increased sooner than in the previous developmental period. In general, the El mouse seizure might represent an abnormal plastic phenomenon associated with repetition of sensory stimuli in addition to genetic predisposition and ontogenetic development.