The effect of small doses of kainic acid on the area CA3 of the hippocampal formation. An electron microscopic study.

The toxic effect on area CA3 of the hippocampus of the rat of small doses of kainic acid (KA) injected into the lateral ventricles was examined by electron microscopy. The most characteristic feature revealed was degeneration in the pyramidal cell somata and in their dendrites from as early as 3 hr after injection. We found four types of degenerating pyramidal cells probably corresponding to their susceptibility to KA intoxication. We also detected degenerating preterminal axons and terminals in addition to degenerating pyramidal cells and dendrites. Temporary structural alterations of the mossy fiber endings and intimate adhesional contacts the mossy fiber endings were also observed. The response of the glia to the damage area CA3 was an increase in the number of astroglia and macrophages in the early stage followed later by mobilization of microglia and astroglia for the formation of scar tissue.