Anticonvulsant effect of intracortical, chronic infusion of GABA in kindled rats: focal seizures upon withdrawal.

The behavioral and electrographic effects of chronic (7 days), localized infusion of GABA (100 micrograms/microliter) into the somatomotor cortex of fully amygdala-kindled rats is reported. The animals were stimulated once daily until a stage 5 (generalized clonic seizure) was obtained for five consecutive days. After determination of a stable seizure triggering threshold, the rats were implanted with osmotic minipumps (1 microliter/h for 7 days) connected to previously implanted bilateral cannulae. Amygdala stimulation was continued for 14 successive days. GABA infusion reduced the motor seizure without significantly modifying the limbic afterdischarge. This effect lasted until termination of drug application, with recovery of stage 5 convulsions on the following 3 to 5 days. No effects were observed in saline-infused animals or in rats with unilateral GABA treatment. Upon cessation of GABA treatment (removal of the osmotic devices by day 7 postimplantation), spontaneous epileptic discharges localized to the infusion sites appeared. In some animals, the abnormal activity was accompanied by behavioral signs of myoclonus. This cortical hyperexcitability lasted 2 to 24 h, with complete recovery afterward. These data indicate that two types of focal epilepsy may coexist independently in the same animal and provide confirmation of previous observations in the monkey on the existence of a "GABA-withdrawal syndrome" after chronic, focal infusion of the amino acid.