Introduction: The hippocampus was recognized as an important focus of epileptic seizures. A long-term potentiation (LTP) like that of epileptiform activities is considered as synaptic which has been observed for the first time in hippocampal formation. The purpose of the present study was investigating the synaptic plasticity induced by tetanic stimulation at CA1 area of the rat hippocampal slices that were susceptible to epileptic seizures.
Materials and Methods: Epileptiform activities in these slices were induced by the application of pentylenetetrazol (PTZ, 3mM) for 20 miniutes. Neural activity in the form of population spikes in pyramidal cell of CA1 area was recorded before and after tetanic stimulation r PTZ application. Input-output curves of amplitude and delay of population spikes were used to find out changes in synaptic efficacy.
Results: Twenty minutes after PTZ application, and five minutes after tetanic stimulation (in control group), input-output curves had shifted to the left and the shift remained for at least 60 minutes after PTZ washout or tetanic stimulation. PTZ application also led to the appearance of after potentials which maintained for about 30 minutes after PTZ washout. The increase of population spike amplitude induced by tetanic stimulation, in PTZ-treated slices was lower than that of the control one, but the difference between the control and PTZ treated slices was not significant. In addition, to that potentials appeared in PTZ-treated slices following the tetanic stimulation.
Conclusion: The results indicate that PTZ administration for 20 minutes is after sufficient to make up a stable model of epileptic activity. PTZ, like the LTP induced by tetanic stimulation, shifts the input-output curve to the left. Potentiation resulted from LTP was not occluded by the prior PTZ. Therefore, to induce the epileptic activity, a background of potentiation in neural activity is necessary.