Abstracts

Rationale: Gap junctions (GJ) are intercellular channels which can be involved in the generation and propagation of epileptic activity (Trends Neurosci 2000; 23[2]: 68-74), and changes in the expression of connexins (Cx) have been described both in animal models of epilepsy and in patients (Epilepsia 2003; 44[12]: 1596-600). The aim of this study was to evaluate the protein and mRNA levels of Cx in the hippocampus of rats submitted to the pilocarpine (PILO) model of temporal lobe epilepsy (TLE). Besides, in order to verify the effects of a GJ blocker (carbenoxolone - CBX) on the epileptiform discharges and to demonstrate the possible involvement of these channels in the status epilepticus (SE), the electrocorticographic (ECoG) activity of rats submitted to the PILO model was evaluated. Methods: Male Wistar rats were treated with methylscopolamine (s.c., 1 mg/kg) 30 minutes before the PILO injection (i.p., 360 mg/kg). The animals were divided in 3 groups: acute (sacrificed 4 hours after the beginning of SE, n=12), latent (3 days after SE induction, n=14) and chronic (4 months after SE induction, n=15). Their hippocampi were submitted to immunoblotting and real-time PCR protocols for detection of Cx36 and Cx43. To evaluate the effects of CBX on SE, the animals (n=3) were anesthetized and placed in a stereotaxic apparatus to have electrodes implanted in the cortical area A3. After 7 days of recovery, the animals were submitted to the following data acquisition protocol: a) Basal: 30 minutes of recording for adaptation of the animal; b) Methylscopolamine: 30 minutes of recording after the injection; c) PILO/SE: 30 minutes of recording after SE establishment; d) CBX: recording after injection of CBX. Some intervals of the above recordings were chosen for spectral analysis of frequency and power. Results: The immunoblotting data revealed a significant increase (41%) in the expression of Cx36 in the hippocampi of animals analysed in the acute phase. However, the PCR data showed a reduction of the Cx36 mRNA levels in the latent and chronic groups (77% and 58%, respectively). The Cx43 electrophoresis indicated the presence of at least 2 isoforms, named P0 (nonphosphorylated) and P1 P2 (phosphorylated isoforms). An increase of the total amount of protein and of the P1 P2 isoforms was observed during the chronic phase (77% and 81%, respectively). The PCR data revealed a significant increase of Cx43 mRNA only in the latent phase. Treatment with CBX produced a marked decrease in the frequency and amplitude of the epileptiform potentials; moreover, the sharp wave complexes periodically changed their morphology, alternating between polyspike complexes or hypersynchronic slow wave groups, usually sinusoidal without the spike component. Conclusions: The PILO model of TLE appears to induce changes of the expression of Cx in the hippocampus of rats, suggesting an important role for the GJ communication in this pathology. This idea is strengthened by the results obtained with the CBX treatment, which suggested CBX to be an effective compound in the control of SE induced by PILO.