Animal models of
epilepsy are essential for the search of new effective
antiepileptic drugs. Moreover they may lead to the discovery of the basic neuronal dysfunction(s) which underlies human
epilepsies. Animal
epilepsies as well as experimental
seizures are usually considered as valid models of human
epilepsies when, and only when, the drugs which are effective in human
epilepsies prevent
seizures in animals. This, however, precludes finding new drugs for resistant
epilepsies. Animal models of
epilepsy can be classified as follows: (i) experimental
seizures induced by
convulsant drugs or by an electrical stimulation; (ii)
reflex epilepsies; (iii) idiopathic
epilepsies. Examples of animal models of
epilepsy taken from each of these three classes are briefly reviewed.
Seizures induced by
convulsant drugs or by an electroshock are widely used as simple and rapid screening systems for new
anticonvulsant compounds. Moreover, the use of chemical
convulsants can lead to new hypotheses concerning the mechanisms underlying human
epilepsies. Thus, one of the main arguments in favor of the GABAergic hypothesis of
epilepsy is that
GABA antagonists induce
seizures which are readily counteracted by most
antiepileptic drugs. Among the other models of experimentally induced
seizures, the kindling model is usually considered, on the basis of its pharmacological characteristics, as a Grand Mal type
epilepsy model. Thirty years after this model was first described, the exact modifications induced in the brain by the kindling procedure remain unknown. Various animal species exhibit
reflex epilepsies.
Myoclonic seizures can be induced by photic stimulation in Papio-papio baboons;
tonic-clonic seizures can be induced by various auditory stimuli in certain strains of mice and rats; myoclonic and
tonic-clonic seizures can be induced by a variety of environmental stimuli in the mongolian gerbil; photosensitive and
febrile seizures have been described in fowl. Most
antiepileptic drugs are effective in these
reflex epilepsies. Alterations in several
neurotransmitter systems have been reported in susceptible strains as compared to resistant strains, such as modifications in noradrenergic, serotoninergic, GABAergic or glutamatergic transmissions, but no single abnormal parameter can unequivocally be correlated to seizure susceptibility. Idiopathic
epilepsy is not uncommon in dogs and the prevalence of the disease appears to be comparable to that observed in man. Grand Mal type
epilepsy appears to be the most frequent type of
epilepsy in dogs; little work has been devoted to the study of the neurochemical alterations which may underly the disease.