Models of simple partial and absence seizures in freely moving rats: action of ketamine.

The action of ketamine was studied in two models of seizures: a) bilateral neocortical discharges produced by topical application of pentylenetetrazol (model of simple partial seizures); and b) rhythmic spike-and-wave activity induced by systemic administration of pentylenetetrazol (model of absence seizures). Ketamine exerted biphasic effects. In the first model, the dose of 20 mg/kg ketamine significantly suppressed the ictal neocortical discharges (i.e., continuous spiking or ictal activity) accompanied by clonic motor seizures. However, at the dose of 40 mg/kg ketamine significantly accentuated the onset and increased the number of individual discharges (interictal spikes) in bilateral neocortical foci. In the model of rhythmic spike-and-wave activity, the lower dose of ketamine (20 mg/kg) decreased the number of rhythmic spike-and-wave episodes when compared to the higher dose (40 mg/kg) of ketamine, which increased the number of episodes. However, neither result differed significantly from control values. The present results suggest a dose-dependent action of ketamine: Lower doses (10 and 20 mg/kg in the rat) are able to suppress seizure activity, whereas a higher dose (40 mg/kg) potentiates the seizures. Moreover, the action of ketamine may be dependent upon the seizure model used. The study presents a new model of acute epileptic focus in freely moving rats.