Localization of the origin of metrazol-induced rhythmic electrocorticographic activity in rats

In acute experiments we studied the structures essential for the genesis of rhythmic electrocorticographic activity composed of spike-and-wave rhythm of 5 Hz frequency evoked in rats by the systemic administration of pentamethylenetetrazol. Brain stem transection at intercollicular level did not prevent this rhythmic activity from developing. Episodes of this activity were suppressed during a wave of thalamic spreading depression--in every case on the side of depression and in more than half the cases also in the contralateral hemisphere. We further observed that the effect on rhythmic activity in the sensorimotor and visual region was unequal. It can be concluded that the thalamocortical system is essential for the development of rhythmic metrazol spike-and-wave activity, but that this system is not functionally homogeneous.