Long-term effects of pilocarpine in rats: structural damage of the brain triggers kindling and spontaneous recurrent seizures.

Structural damage of the human brain (perinatal damage, cerebral trauma, head injury, cerebrovascular and degenerative diseases, intracranial tumor, metabolic diseases, toxins, drug-induced seizures) may lead to chronic epilepsy in survivors. Epidemiologic analyses show that a considerable time-delay occurs between the exposure of the brain to injury and the appearance of seizures. Such seizures are usually partial or mixed, may develop at any age, and are difficult to treat. In rats subjected to structural damage of the brain induced by sustained convulsions triggered by systemic administration of the cholinergic agent pilocarpine, spontaneous seizures may develop after a mean latency of 14-15 days. The mean frequency of spontaneous recurrent convulsions remains constant for several months. Evolution of these convulsions proceeds through several electrographic and behavioral stages resembling kindling. Kindling may be otherwise induced in rodents by repeated systemic administration of convulsants or by repeated electrical stimulation of sensitive brain regions. These observations demonstrate that structural damage of the brain may lead to spontaneously recurrent convulsions (chronic epilepsy) in rats and that kindling may be involved in the evolution of such a condition. This finding suggests that kindling mechanisms underlie the development of epileptic foci from structural brain lesions. Such mechanisms may be involved in the etiology of some forms of epilepsy in humans.