Abstracts

cAMP-dependent protein kinase (PKA) and calcineurin are major modulators of synaptic transmission likely to be involved in molecular and cellular events leading to epileptogenesis, but little is known about how they affect the onset of acute epileptic seizures. In this study, we have used ascomycin, a calcineurin inhibitor, and H-9 dihydrochloride, a PKA inhibitor, in order to investigate the role of both enzymes in seizures induced by microperfusion of picrotoxin in the rat hippocampus. We used a CMA/120 system for freely moving animals. Rat hippocampus was perfused with ringer fluid through CMA/12 microdialysis probes at a flow rate of 2 ml/min during 3 hours with continuous EEG and videotape recording. After 2 hours, Ringer was substituted by a picrotoxin solution (100-300 [mu]M) during 5 min. The same protocol was repeated in each rat with continuous perfusion of ascomycin (100 [mu]M) and H-9 dihydrochloride (100 [mu]M). Continuous perfusion of H-9 dihydrochloride (100 [mu]M) protected completely against picrotoxin seizures in 37.5% of the animals and significantly reduced the mean number of seizures (from 2.38 [plusmn] 0.52 to1.6 [plusmn] 0.3, P[lt] 0.01) and the mean seizure duration (from 43.8 [plusmn] 14.2 to 21.2 [plusmn] 6. 9, P[lt] 0.01). 100[mu]M ascomycin completely supressed seizures in 75% of the animals, and significantly reduced seizure duration and severity in non-protected rats. Mean seizure duration (23 [plusmn] 6.9 s; p[lt]0.01) and mean number of seizures (0.46 [plusmn] 0.12; p[lt]0.01) were also significantly decreased. This study provides additional evidence of the involvement of phosphorylation/dephosphorylation mechanisms in the development of epileptic seizures. Our results show in vivo that calcineurin and PKA participate in the mechanisms of picrotoxin-induced epileptic seizures in the rat hippocampus, and support previous data suggesting that calcineurin and PKA inhibition may be a possible strategy in the search for new anticonvulsant drugs.[figure1] (Supported by grant XUGA PGIDIT03PXIB20803PR from the Conseller[iacute]a de Educaci[oacute]n e Ordenaci[oacute]n Universitaria, Xunta de Galicia, Galicia, Spain.)