THE EFFECTS OF MALIGNANT GLIOMA ON THE EEG AND SEIZURE THRESHOLDS - AN EXPERIMENTAL-STUDY

Generalised or partial seizures are a common problem with many suprate ntorial gliomas. Their underlying pathophysiological mechanisms are po orly understood. To investigate this problem clinical and EEC seizure thresholds were investigated in experimental rodent gliomas using the epileptogenic drug pentplenetetrazole (PTZ). Mixed C6/A15A5 malignant gliomas were grown in adult Wistar rats after unilateral stereotactic implantation of a 50 : 50 cell mix into the caudoputaminal region. Ele ven to 14 days later EEG (raw and spectrally analysed) was recorded bi laterally from the frontal and parietal regions under mixed alpha-chlo ralose and urethane anaesthesia. Baseline EEG (15 minutes), EEG during and after (30 minutes) PTZ infusion (100 mu l/min) and the time to ap pearance of seizure manifestations after starting PTZ were recorded. F ourteen animals were studied (5 normal, 5 with tumours, 4 sham implant s) and mean BP, PaCO2, PaO2 and temperature were similar in the three groups. Baseline raw EEG showed predominate slow wave activity with lo wer amplitude and less spontaneous activity overlying tumours. Followi ng PTZ infusion a sequence of vibrissal twitching (following a mean of 14.5 mg/kg PTZ in control and sham animals); jaw/nasal twitches (17.5 mg/kg); fore and hind limb jerking (46 mg/kg); myoclonic jerking (47 mg/kg); and status (77.5 mg/kg) was observed. The seizure thresholds f or all PTZ induced seizure phenomena were, except for status epileptic us, highest in the tumour bearing animals. The time to 70% seizure act ivity on the EEG was also significantly longer in the tumour bearing a nimals. Spectral analysis of the EEG, although showing increased alpha and theta activity after PTZ infusion, did not discriminate between t he three experimental groups either before or after PTZ activation. Th ese studies have confirmed that experimental gliomas alter baseline EE G and both the EEG and behavioural response to PTZ. The reasons for th e raised seizure threshold in the glioma bearing animals and the relev ance of this experimental paradigm to human tumour associated epilepsy are discussed.