Specific and non-specific multiple unit activities during pentylenetetrazol seizures in animals with mesencephalic transections.

A group of cats with brain stem transection at the mesencephalic level was studied during the administration of convulsive doses of pentylenetetrazol in regard to changes in EMG multiple unit activity (MUA), as a method to determine the course of muscular convulsions and their relation with EEG and MUA changes in the motor cortex, pyramidal tract and mesencephalic and pontine reticular formations. PTZ induced significant increase in the duration of EMG tonic convulsions, lasting 3-100 times longer than the entire tonic-clonic seizure seen in intact animals after similar doses of PTZ and not accompanied by EEG or pyramidal tract "seizures", but by an equally long-lasting increase in MUA of mesencephalic and pontine reticular formations. Comparing present results with those seen in intact, "encéphale isolé" and "pretrigeminal" preparations, it is concluded that the mesencephalon is important for both: activating tonic phase of the convulsions and the EEG changes seen in PTZ-induced seizures. It also suggests that termination of seizures is due to inhibitory influences of supramesencephalic structures.