EXAMINATION OF PERSISTENT EFFECTS OF REPEATED ADMINISTRATION OF PENTYLENETETRAZOL ON RAT HIPPOCAMPAL CA1 - EVIDENCE FROM IN-VITRO STUDY ON HIPPOCAMPAL SLICES

The early and long-lasting effects of pentylenetetrazol-kindling on hi ppocampal CA1 synaptic transmission were investigated. Experiments wer e carried out in the hippocampal slices from control and kindled rats at two post-kindling periods, i.e. 48-144 h (early phase) and 30-33 da ys (long-lasting phase). Field potentials, i.e. population excitatory postsynaptic potential (pEPSP) and population spike (PS) were recorded at the stratum pyramidale following stimulation of the stratum radiat um. Kindling-induced changes in synaptic transmission were assessed by stimulus-response functions and paired-pulse responses. The results s howed that 48-144 h after kindling, the PS amplitude in the CA1 of kin dled slices enhanced, and a second PS appeared compared to control sli ces. But at 30-33 days after kindling, the pEPSP slope in the CA1 of k indled slices enhanced without any change in the PS compared with thos e in the control slices. Evaluation of paired-pulse responses showed a significant reduction in paired-pulse inhibition for PS 48-144 h afte r kindling and a significant increase in paired-pulse inhibition for p EPSP 30-33 days after kindling. Our results suggest that pentylenetetr azol-kindling is accompanied by enhanced excitability and a reduction of paired-pulse inhibition in hippocampal CA1. The increased paired-pu lse inhibition one month after kindling, may be interpreted as an adap tive process to cope with subsequent seizures.