The action of ethosuximide, valproate and clonazepam against pentylenetetrazol-induced epileptic EEG phenomena was studied in acute experiments in rats with intercollicular brainstem transection. Ethosuximide lost its action against both rhythmic metrazol activity (model of human absences) and EEG seizures. On the contrary, the action of valproate and clonazepam in cerveau isolé rats was the same as in intact animals. The site of anticonvulsant action of ethosuximide may be localized in hindbrain structures, whereas the actions of both valproate and clonazepam may be demonstrated even if hindbrain structures had been eliminated.
In a previous study of a kindling model using stimulation of the entorhinal cortex we found a redistribution of synaptic vesicles into the close vicinity of the active zone of synapses of Type I (Gray 1959) in the hippocampal gyrus dentatus. In this paper, ultrastructural studies of the same model are being continued using planimetry of the synaptic apparatus. A significant increase of the postsynaptic apparatus, area enlargement by 53 %, increase of the perimeter by 28 % and shape irregularity are being reported. No changes in shape or in size have been demonstrated in presynaptic structures or in the morphology of presynaptic mitochondria. These findings are discussed in relation to increased functional readiness of the synapses as signs of active reconstruction of the synaptic apparatus.
The possible protective action of pramiracetam, a pyrrolidinone nootropic drug, against hypobaric hypoxia was studied in two age groups of immature rats with implanted electrodes. Epileptic afterdischarges induced by hippocampal stimulation were used as a measure of hypoxic damage. Pramiracetam did not substantially change these afterdischarges in 12- and 18-day-old rat pups which were not exposed to hypoxia. Hypobaric hypoxia (simulated altitude of 7000 m for one hour) led to prolongation of the first afterdischarge in both age groups. Pramiracetam did not influence this prolongation in 12-day-old rats. The first afterdischarge was shortened significantly in 18-day-old animals but not to the level of rats not exposed to hypoxia. The afterdischarges elicited by repeated stimulations (four times at 10 min intervals) did not differ in pramiracetam-treatcd and control rats.
Epileptic afterdischarges induced by electrical stimulation of the sensorimotor cortex as well as minimal metrazol seizures are characterized by EEG spike-and-wave rhythm and nearly the same motor pattern of clonic seizures. The action of ethosuximide on these two models was tested in adult rats with implanted electrodes. Cortical afterdischarges remained practically uninfluenced by ethosuximide (62.5 or 125 mg/kg i.p.) whereas minimal metrazol seizures were suppressed in a dose-dependent manner (doses of 31.25, 62.5 and 125 mg/kg i.p. were used). Present results in connection with recent data on the abolition of spike-and-wave rhythm elicited by low systemic doses of pentylenetetrazol suggest that spike-and-wave rhythm does not represent a single entity.