THE AMYGDALA IS CRITICAL FOR SEIZURE PROPAGATION FROM BRAIN-STEM TO FOREBRAIN

Audiogenic seizures, a model of brainstem epilepsy, are characterized by a tonic phase (sustained muscular contraction fixing the limbs in a flexed or extended position) associated with a short cortical eletroe ncephalogram flattening. When sound-susceptible rats are exposed to re peated acoustic stimulations, kindled audiogenic seizures, characteriz ed by a clonic phase (facial and forelimb repetitive jerks) associated with cortical spike-waves, progressively appear, suggesting that repe tition of brainstem seizures causes a propagation of the epileptic dis charge toward the forebrain. In order to determine the structures thro ugh which this propagation occurs, four kinds of experiments were perf ormed in non-epileptic rats and in sound-susceptible rats exposed to s ingle or repealed sound stimulations. The following results were obtai ned: (1) Electrical amygdalar kindling was similar in non-epileptic an d naive-susceptible rats, but was facilitated in sound-susceptible rat s submitted to 40 acoustic stimulations and presenting kindled audioge nic seizures. (2) Audiogenic seizures induced an increase in [C-14]2-d eoxyglucose concentration in the amygdala after a single seizure, and in the amygdala, hippocampus and perirhinal and piriform cortices afte r a kindled audiogenic seizure. (3) A single audiogenic seizure induce d the expression of c-Fos protein mainly in the auditory nuclei. A few cells were stained in the amygdala. After 5-10 audiogenic seizures, a clear staining appeared in the amygdala, and perirhinal and piriform cortices. The hippocampus expressed c-Fos later, after 40 audiogenic s eizures. (4) Injection of lidocaine into the amygdala did not modify s ingle audiogenic seizures, but suppressed myoclonias and cortical spik e-waves of kindled audiogenic seizures. Similar deactivation of the hi ppocampus Failed to modify kindled audiogenic seizures. Taken together , these data indicate a critical role for the amygdala in the spread o f audiogenic seizures from brainstem to forebrain. (C) 1997 IBRO. Publ ished by Elsevier Science Ltd.