Characteristics and origin of frontal paroxysmal responses induced by light stimulation in the Papio papio under allylglycine.

In the Papio papio, curarized and rendered photosensitive by injection of a subconvulsant dose of DL-allylglycine, single flashes induce frontal paroxysmal evoked responses on condition that they be preceded by trains of intermittent light stimulation (ILS). The characteristics of these responses have been compared to those of non-paroxysmal responses induced in the same cortical area by isolated flashes (not preceded by trains of ILS). The paroxysmal responses resemble spikes and waves and consist of one or two positive spikes followed by a slow negative wave. The intracortical distribution of these responses has been studied in the motor cortex. The non-paroxysmal responses are probably not generated at this level. On the other hand, observations made during paroxysmal responses show the existence of two cortical responses; this demonstration follows from the existence of an inversion in some response components, linked to a negativity and a local cellular activation. A generator, situated in the pyramidal cell layer, is active during the positive surface spikes; the other generator, situated in the more superficial cortical layers, is active at the beginning of the slow negative surface wave. The cortical and subcortical afferents likely to bring these generators into play are discussed.

[Modification of frontal and occipital cortical excitability provoked by trains of flashes in Papio papio (author's transl)]. / Modifications de l'excitabilite corticale (frontale et occipitale) par des trains d'eclairs chez le singe Papio papio.

The experimental conditions necessary for obtaining an evoked paroxysmal response from the frontal cortex were studied in the baboon Papio papio. The trigger stimulus was comprised of an isolated flash preceded by a train of intermittent light stimulation (SLI). Two conditions were necessary for the appearance of paroxysmal responses: a subconvulsant dose of DL-allylglycine had to be injected at least 3 h previous to recording, and a sufficient number of SLI trains had to be presented to the animal. The paroxysmal responses disappeared as soon as SLI trains were stopped. At the same time, modifications in the evoked occipital potential continue, although these do not become paroxysmal. These modifications appear either simultaneously with or previous to the paroxysmal frontal response.

Absence of seizure activity following focal cerebral injection of enkephalins in a primate.

Baboons (Papio papio) with photosensitive have been chronically prepared with guide cannulae and deep electrodes to study the effects of focal injections of opioids. In the hippocampus, amygdala and thalamus (centre median) 50--100 micrograms morphine, 20--100 micrograms Met-enkephalin or 2--10 micrograms FK 33,824 do not induce local or general electrographic or motor signs of epilepsy. The acute epileptogenic effect of morphine and enkephalins observed in rats is not a general phenomenon whereas the anticonvulsant action of opioids acting on mu-receptors is seen in rodents and primates.

Cortical unit activity during intermittent photic stimulation in Papio papio. Relationship with paroxysmal fronto-rolandic activity.

Extracellular records have been made in the fronto-rolandic (FR), parietal and occipital cortical areas in Papio papio injected with allylglycine and paralysed with a synthetic curarizing agent. The organization of the unit discharges in the absence of intermittent light stimulation (ILS) is normal. During ILS, unit discharges in the FR cortex are organized in bursts of high frequency that are synchronous with the spikes of the EEG paroxysmal discharges (PD) in the same territory; this burst-organized FR activity is reversible, and bursts disappear when the ILS stops. In addition, in the FR cortex, triple or single flashes induced paroxysmal visual evoked potentials (PVEP) whose spikes were accompanied by bursts identical to the preceding ones. The slow waves which constituted the PD and the PVEP corresponded to a transitory inhibition of the FR neuronal activity. From the unit discharge patterns, no difference was observed between the two EEG paroxysmal activities recorded. No pattern of discharge in bursts was ever observed in the parietal and occipital cortex. The synchronizing role of the light stimulation in the FR cortex in Papio papio under allylglycine is discussed and the results are used to compare the experimental model with the naturally highly photosensitive animal. The particular reactivity of the FR cortex with respect to other regions is also discussed. Finally, the results bring forth new information in favour of a similarity between PD and PVEP.

Sustained limbic seizures induced by intraamygdaloid kainic acid in the baboon: Symptomatology and neuropathological consequences.

In Papio papio baboons chronically prepared for cortical and deep electroencephalographic recording, injection of kainic acid into the amygdala (7 animals) or temporal pole (2 animals) gave rise to focal epileptic discharges lasting 15 to 150 hours. Electrographically, the seizure activity spread ipsilaterally and contralaterally within the limbic system but did not become generalized. The principal associated motor signs were arrest of movement and oral automatisms. Histological examination after two to ten days demonstrated lesions (neuron loss and gliosis) at the injection site that varied according to the amount of kainic acid injected (2 to 68 microgram). "Remote" lesions occurred in the ipsilateral hippocampus (end-folium and Sommer sector) and neocortex (occipital and frontal regions). The hippocampal lesions were comparable to those previously described as consequent to status epilepticus.