Changes in the EEG-reactions to repetitive peripheral and central electrical stimulation by intraraphedorsal kainic acid in the cat.

The effect of kainic acid (KA) microinjected into the dorsal raphe nucleus (NRD) of the cat through glass micropipette by means of an air pressure system in doses ranging from 2.3 to 23.5 nmol on the electroencephalographic (EEG)-reactions elicited by repetitive (6-10 Hz) peripheral (somatic and visual) or central electrical stimulation was investigated. A significant facilitation of the driving reaction evoked by rhythmic subcutaneous electrical stimulation of the forepaw was found after KA, while the driving reaction elicited by repetitive photostimulation did not change. The cortical rhythmic reactions to repetitive electrical stimulation of the specific and nonspecific nuclei of the thalamus and of the caudate nucleus (where inhibitory mechanisms are known to be involved) diminished or disappeared when generalized paroxysmal spontaneous activity occurred after kainic acid. The EEG-reaction to stimulation of the mesencephalic reticular formation was significantly facilitated after KA. The repetitive electrical stimulation of the ventral posterolateral nucleus, the centre median and the mesencephalic reticular formation also provoked the appearance of paroxysmal EEG activity or afterdischarge which in some cases developed into epileptic seizures. The data show that kainic acid injected into the dorsal raphe nucleus increases (probably by disinhibition) the excitability level of some forebrain structures connected with the nucleus.