EPILEPSY INDUCED COLLATERAL SPROUTING OF HIPPOCAMPAL MOSSY FIBERS - DOES IT INDUCE THE DEVELOPMENT OF ECTOPIC SYNAPSES WITH GRANULE CELL DENDRITES

In the present study. using Golgi and electron microscopy techniques, experimentally induced epilepsy (kindling and kainate treatment) elici ted collateral sprouting of mossy fibers in rat hippocampus. Collatera l branches invade the hilus, cross the granule cell layer, and distrib ute throughout the inner third of the molecular layer. These newly dev eloped collaterals may acquire the typical features of mossy fibers in cluding giant fiber varicosities (mousses), although the mean surface of these mousses was thinner in these collaterals than in terminal bra nches. Granule cell dendrites may develop giant thorny excrescences, s uggesting that the targets of these collaterals are granule cells. Gia nt synaptic boutons appear in the inner third of molecular layer of ep ileptic rats. These boutons acquire the morphological features of moss y fiber boutons and made multiple synaptic contacts with dendritic spi nes. The analysis of the profile types suggests that some of the newly developed collateral mossy fibers made hypotrophic synaptic contacts.