SYNAPTIC VESICLE SIZE AND SHAPE PROFILE IN THE KINDLING MODEL OF EPILEPTOGENESIS

Excitatory synapses were studied in the dentate gyrus ipsilateral to s timulated entorhinal cortex in fully kindled rats 2 weeks after the la st (3rd) stage 5 seizure. In previous studies of the same model marked redistribution of synaptic vesicles to a 'strategic position' in the vicinity of the synaptic cleft and a significant enlargement of postsy naptic element were described. In this study the size and shape of syn aptic vesicles were evaluated in three zones parallel to the presynapt ic membrane of the synaptic cleft. The first zone (0.1 mu m) directly adjoined the active zone of presynaptic membrane, the second was from 0.1 to 0.2 mu m and the third from 0.2 to 0.3 mu m from the presynapti c membrane. The vesicles of both the experimental and control animals were significantly smaller in zone I than in zone II and III and, in t he control animals there was a tendency of vesicles to diminish toward s the active zone. Such a tendency was not observed in the experimenta l animals, the largest vesicles were in the middle of zone II and were significantly more rounded in comparison to the vesicles in the contr ols. On the contrary, the vesicles in zone I and III were more elongat ed in the experimental animals than in controls. Our results may be ta ken as a sign of active reconstruction of synaptic apparatus in relati on to increased functional readiness of the synapses. Possible mechani sms as well as significance for the kindling and epileptogenesis are d iscussed. (C) 1997 Elsevier Science B.V.