Effects of brain surgery and EEG operant conditioning on seizure latency following monomethylhydrazine intoxication in the cat

Monomethylhydrazine (MMH) is a highly convulsive methyl derivative of hydrazine. The generalized tonic-clonic seizures elicited by this compound are unusual because of a characteristic latent period between administration and seizures. Evidence indicates that the duration of this latent period can reflect seizure susceptibility in relation to this drug. In the present study this concept was utilized to evaluate the influence of chronic electrode implantation and subsequent EEG operant conditioning on seizure susceptibility in the cat. Thirty cats were studied in three groups of 10 each. One group consisted of unoperated animals, another of operated animals with a diversity of electrode placements and experimental treatments, and the third of operated animals provided with 3 months of sensorimotor EEG operant conditioning. The EEG pattern rewarded was rhythmic, 12 to 16 cps activity, termed the sensorimotor rhythm. Seizure response was measured as the latency, in minutes postinjection, to the onset of generalized tonic-clonic seizures following intraperitoneal administration of 10 mg/kg MMH. Operated animals with either no EEG conditioning or noncontingent conditioning showed significantly shorter and more stable seizure latencies than either the unoperated group or the operated group with sensorimotor-rhythm conditioning. These data indicate that the surgical procedures used increased seizure susceptibility in this paradigm, and that sensorimotor-rhythm operant conditioning countered this effect. Furthermore, the marked variability in seizure latencies noted among unoperated and trained animals suggested individual differences in seizure susceptibility and in response to operant conditioning, respectively.