Repeated long-term potentiation induces mossy fibre sprouting and changes the sensibility of hippocampal granule cells to subconvulsive doses of pentylenetetrazol

Electrical and chemical kindling induces sprouting of the mossy fibre syste m and potentiation of evoked field potentials in the dentate gyrus. It has been postulated that such changes may also be induced by repeated induction of long-term potentiation (LTP) with tetanic stimulation of the perforant pathway. LTP was induced in rats chronically implanted with stimulation ele ctrodes in the ipsilateral and contralateral angular bundles and with a rec ording electrode in the ipsilateral dorsal dentate gyrus. The animals were stimulated 10 times on 10 consecutive days but with different tetanization strengths. Sprouting of the mossy fibres terminating in the CA3 region was significantly induced only in the group of 'strongly' tetanized animals, bu t not in that of 'weakly' tetanized animals, or in low-frequency stimulated animals. Additionally, a novel form of potentiation which was previously f ound in pentylenetetrazol (PTZ)-kindled animals was also observed in the gr oup of 'strongly' and 'weakly' tetanized rats. Differences in duration of t his potentiation were found between the two groups of animals tetanized wit h different strengths. The results further demonstrate that morphological a nd functional changes in the hippocampus, similar to those seen after kindl ing, can also occur in an activation paradigm leading to long-lasting synap tic plasticity but not accompanied by seizure activity.