Immature rabbit hippocampus is damaged by systemic but not intraventricular kainic acid

Intraventricular injection of kainic acid produced a characteristic necrosis in the hippocampal CA3 region of adult rabbits. Neurons in immature rabbit hippocampus were relatively insensitive to the intraventricular neurotoxin, even though these injections caused seizures. In contrast, the immature hippocampus was highly sensitive to kainate delivered systemically. Systemic kainate preferentially killed neurons in the CA1 region, not the CA3 region, of immature animals. Kainate injections also caused cellular damage in brain regions other than hippocampus. In immature rabbits, the pattern of extra-hippocampal damage was similar regardless of the route of kainate delivery. This pattern of extra-hippocampal damage was distinctly different than that seen in adults following intraventricular kainate. These data suggest that kainate-induced damage in the CA3 and CA1 regions of the hippocampus are mediated by different mechanisms. Furthermore, the dissimilar patterns of extra-hippocampal damage in immature and adult rabbits suggest that mature and immature animals have differential sensitivity to kainate, different types of kainate binding sites, and/or different distributions of kainate receptors.