Audiogenic kindling in the Wistar rat: a potential model for recruitment of limbic structures

Repetitive high intensity (110 dB) sound stimulation induces a forebrain-ki ndling phenomenon in animals predisposed to sound induced seizures. Wistar audiogenic rats (WARs) have been reported to develop a mixed brainstem-limb ic seizure pattern, after more than five to ten stimuli. Besides the origin al brainstem wild running and tonic-clonic seizures, new behavioral pattern s appear resembling those of electrical amygdala kindling. Although audioge nic kindling is a well-known phenomenon, electrographic limbic recruitment during the kindling has never been reported. Our objective was to use elect rophysiology to test the hypothesis of gradual and sequential involvement o f the amygdala and then cortex during audiogenic kindling. We used video-EE G recordings with cortical and deep electrode implants (inferior colliculus and basolateral amygdaloid nuclei) during audiogenic kindling on eight WAR s, and their respective controls, submitted to a protocol of three acoustic stimuli per day. A new design for 'on site' source follower circuits was u sed in order to minimize noise during the recording of EEG data from the wi ld running episode and the subsequent tonic-clonic or motor limbic seizures . The video-EEG equipment assembled allowed synchronous recordings of both behavior and EEG. WARs first recordings showed electrodecremental responses after seizure onset and a probable epileptiform activity, particularly in the inferior colliculus, during the tonic phase of seizure. All animals sho wed very similar polyspike-wave activity in the amygdala, after behavioral seizure patterns (Racine's scale) occurred. The morphology of such epilepti form EEG activity is very similar to that reported for electrical amygdala kindling. Also, when audiogenic kindling continued, both inferior colliculu s and cortical electrodes presented high amplitude and synchronized epilept iform polyspike activity. (C) 2000 Elsevier Science B.V. All rights reserve d.