Stimulation induced changes in extracellular free calcium in normal cortex and chronic alumina cream foci of cats

Abstract

Changes in extracellular [Ca 2+] 0 (δ Ca) were measured with ion selective microelectrodes in the sensorimotor cortex of cats, surrounding alumina cream lesions and in the contralateral homotopic cortex. The lesions were produced by topical application of alumina cream 6 months-6 years prior to experiments. In normal cortex, stimulus induced reductions of [Ca 2+] 0 were found to be maximal (up to 0.45 mM) in depths of 200–300 μm below the cortical surface. At depths of 600 μm and more below the cortical surface, [Ca 2+] 0 usually rose by up to 0.2 mM above baseline. In the vicinity of the chronic lesion as well as in contralateral cortex [Ca 2+] 0 fell initially during stimulation in all depths. close to the lesion δ Ca was as high as 0.8 mM and sites of maximal δ Ca were found to be located deeper in the cortex. About 5 mm from the scar as well as in the contralateral homotopic cortex, maximum δ Ca levels were found in a depth of 200–300 μm. It is suggested that Ca 2+ dependent mechanisms are involved in epileptogenesis in chronic epileptic foci.