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Abstract
The neurotoxic properties of ibotenate and kainate after intracerebral application
were compared in several regions of the rat brain. Ibotenate, being 5-10 times less
toxic than kainate, caused lesions which were generally found to extend spherically
from the tip of the injection cannula. In contrast, kainate injections often resulted
in neuronal degeneration distant from the site of infusion, thus severely limiting
its use as a tool for causing lesions in neurobiological studies. In some of the brain
regions examined (hippocampus, septum), neurons appeared differentially susceptible
to kainate but uniformly vulnerable to ibotenate. Some cell groups, such as those
in the medial septum and the locus coeruleus, proved highly resistant to kainate but
could be selectively ablated by ibotenate. These findings, together with differences
between the two toxins in the evolution of neuronal degeneration (exemplified here
in the hippocampal formation), appear to support previous suggestions that ibotenate
and kainate exert their excitotoxic actions via different mechanisms. On the other
hand, neuropathological changes caused in the cerebellum did not differ, since both
ibotenate and kainate preferentially destroyed granule cells. Two nuclei, the arcuate
nucleus of the hypothalamus and the nucleus of the fifth nerve, were found to be extremely
resistant to either neurotoxin.