1. Rats with spontaneous recurrent seizures (SRS) were obtained by inj
ection of kainic acid (KA; 10 mg/kg SC) to drug-naive rats that regula
rly 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 S
C). The seizures induced in SRS rats by KA were similar to SRS regardi
ng their clinical stage and duration (mean duration of seizures: 44 se
c and 43 sec, respectively). The frequency of seizures was, however, i
ncreased compared with the frequency of SRS in control, vehicle-treate
d SRS rats (mean frequency of seizures: 12.9 and 0.4 per 3 hr, respect
ively). The KA-induced seizures in SRS rats differ behaviorally from K
A-induced seizures in naive rats-namely, neither wet dog shakes nor th
e status epilepticus could be induced. 3. Repeated injection of an equ
al dose of KA, applied to the SRS rats 1 day after the previous KA cha
llenge, 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. (C)
1998 Elsevier Science Inc.