Amygdaloid kindling with bicuculline methiodide in rats

The effect of repeated intraamygdaloid injection of bicuculline methiodide (BM) was studied in rats. Chemitrodes for both microinjection and electrographic recording were implanted into the left basolateral amygdala. Two weeks after the surgery, a subconvulsive dose of BM (0.2 or 0.4 nmol) was administered through the chemitrodes every fourth day. Repeated injections caused a progressive seizure development which was comparable to that seen with electrical kindling. The kindling effect persisted after a 6-month interruption of the stimulation. When a mixture of BM and GABA agonist (GABA 20 nmol, muscimol 2 nmol, or baclofen 5 nmol) was injected into the amygdala of kindled rats, seizure activity was markedly suppressed to stage 0 or 1. On the other hand, an intraamygdaloid injection of picrotoxin (0.8 nmol) brought about the same seizure as induced by BM, whereas no seizure was observed with strychnine (4 nmol). No histological change specific to this kindling was detected. The present results indicate that chemical kindling can be induced by repeated local injection of BM into the amygdala, and that the mechanism underlying this kindling is closely associated with local postsynaptic GABA receptors in the amygdala. This GABAergic system may also be important in other types of kindling.