Rats with spontaneous recurrent seizures (SRS) were obtained by injection of kainic acid (KA; 10 mg/kg SC) to drug-naive rats that regularly developed wet-dog shakes followed by complex partial seizures and status epilepticus. Three to five weeks later, the rats with manifest SRS were selected. 2. The SRS rats were challenged with KA (10 mg/kg SC). The seizures induced in SRS rats by KA were similar to SRS regarding their clinical stage and duration (mean duration of seizures: 44 sec and 43 sec, respectively). The frequency of seizures was, however, increased compared with the frequency of SRS in control, vehicle-treated SRS rats (mean frequency of seizures: 12.9 and 0.4 per 3 hr, respectively). The KA-induced seizures in SRS rats differ behaviorally from KA-induced seizures in naive rats-namely, neither wet-dog shakes nor the status epilepticus could be induced. 3. Repeated injection of an equal dose of KA, applied to the SRS rats 1 day after the previous KA challenge, did not induce seizures. The loss of seizure susceptibility to KA was only temporary, as shown after a 7-day drug-free period, when the repeated injection of KA regained its seizure-triggering capacity. 4. The results indicate that reactivity to the seizure-inducing agent kainic acid changes in rats with spontaneous recurrent seizures.
