Electroencephalographic study of the GABA-withdrawal syndrome in rats.

The spatial and temporal EEG features of the epileptogenic syndrome induced by cessation of chronic intracortical GABA infusion in normal rats are described. In the initial stages, the paroxysmal discharges (PDs) induced by withdrawal from unilateral GABA application may appear either unilaterally or bilaterally, although with greater amplitude on the infused side. PDs are transitorily accompanied by behavioral signs of distal myoclonus of the body territory corresponding to the infused area (contralateral hindlimb). Later, the paroxysmal activity becomes more localized, circumscribed to the cannula-infused site and with ipsilateral propagation to anterior cortical areas. The amplitude of PDs decreases progressively while their frequency increases, reaching its maximal value at about 4 h after the first PDs have appeared. In the final stages of the syndrome, which may last several days, clinical manifestations are absent and PDs are activated by slow-wave sleep and reduced during REM sleep and waking. Chronic intracortical applications of taurine failed to induce any electroclinical changes on withdrawal and were unable to inhibit the focus elicited by GABA withdrawal, whereas reinstatement of GABA infusion into the epileptogenic area was effective in blocking the paroxysmal activity. Intracortical infusion of baclofen induced the appearance of an epileptogenic focus that waned on withdrawal. The GABA-withdrawal syndrome appears to be a new model of focal status epilepticus; it may be useful as an experimental model of human partial epilepsy to investigate the role of GABAergic neurotransmission.