ALTERATIONS OF NEURONAL FIBERS AFTER EPILEPTIC ACTIVITY-INDUCED BY PENTYLENETETRAZOLE - FINE-STRUCTURE INVESTIGATED BY CALCIUM CYTOCHEMISTRY AND NEUROBIOTIN LABELING (BUCCAL GANGLIA, HELIX-POMATIA)

The influence of epileptic activity on both the fine structure of neur onal processes and the subcellular distribution of calcium-binding sit es was investigated in an epileptic model system, the buccal ganglion of Helix pomatia. Pentylenetetrazole was used to induce epileptic acti vity. Calcium-binding sites were visualized as electron-dense precipit ates. Epileptic and control activity was intracellularly recorded from neuron B3 labeled with neurobiotin. After epileptic treatment, many p rocesses contained vacuolated or electron-lucent areas next to morphol ogically intact areas. Most of these areas were enveloped by layers of endoplasmic reticulum. Lamellar formations of membranes occurred freq uently. Calcium cytochemistry revealed a high content of dense precipi tates within these formations of the endoplasmic reticulum. Local accu mulations of diffuse precipitates were more frequent after epileptic a ctivity than in controls. In contrast, structures such as lamellar bod ies, cytosomes, and synapse-like formations, all of which contained ma ny electrondense precipitates, were apparently unchanged after epilept ic activity. This study demonstrates that epileptic activity can lead to local degeneration of neuronal fibers and an associated increase in calcium-binding sites. It is suggested that calcium sequestration is locally increased within neuronal processes during epileptic activity.