Dual effects of glutamate on cyclic AMP levels in slices of rat cerebral cortex with an iron-induced epileptic focus.

An epileptic focus not resulting in generalized convulsions was induced by a microinjection of ferric chloride solution into the left anterior cortex of rats. The formation of the epileptic focus was confirmed by the appearance of bilateral spike and slow wave complexes as well as focal isolated spikes in electrocorticograms (ECoGs). The effect of glutamate on cyclic AMP accumulation was examined in incubated slices prepared from four quadrants of the epileptic cortex. In animals showing isolated spikes 8 to 10 days after the microinjection, the effect of glutamate on cyclic AMP accumulation was stimulatory. It was greatest in the left anterior quadrant which included the injection site, but only slight in the left and right posterior quadrants. In animals showing spike and slow wave complexes 30 to 60 days after the microinjection, the stimulatory effect of glutamate was also most pronounced in the left anterior quadrant. In the right anterior and the left posterior quadrants glutamate had almost no effect, while in the right posterior quadrant, glutamate was inhibitory.