[Value of the monkey Papio papio for the study of epilepsy]

The baboon Papio papio is the only animal model showing a natural photosensitive epilepsy very similar to that observed in some human epileptic patients. In the baboon, intermittent light stimulation (ILS) induces bilateral and synchronous myoclonic twitches which are associated with paroxysmal discharges (PDs) predominating in the frontal cortex, and can be followed by generalized tonic-clonic seizures. We were able to demonstrate the motor cortical origin of all these manifestations since neuronal generators responsible for paroxysmal discharges are localized there and are activated by visual afferents from the occipital lobe. The corpus callosum is the structure determining the interhemispheric synchronization of PDs. An unbalance of neurotransmitter systems such as GABA or excitatory amino acids should be responsible for the hereditary predisposition of baboons to photosensitive epilepsy. Some Papio papio, either photosensitive or not, may show spontaneous truncular myoclonic twitches, different from those induced by intermittent light stimulation, and resembling the intention myoclonus as observed in some human neurological disorders (post-anoxic syndrome, degenerative encephalopathies such as Ramsay-Hunt syndrome...). Because of the absence of any abnormal electrographic discharge, this myoclonus is considered non epileptic. Until now, we were unable to determine the structure generating this myoclonus. The most probable origin is in the lower brain stem. Experimental data suggest that a local unbalance of the cholinergic neurotransmission could be responsible for the predisposition of baboons to show this type of myoclonus.