Epidural kainate, but not ibotenate, produces lesions in local and distant regions of the brain. A comparison of the intracerebral actions of kainic acid and ibotenic acid.

Epidural placement of ibotenic acid (Ibo) is described as a new technique for easy and successful lesioning of cortical neurons. The method works reliably without apparent damage to passing or underlying fibers and without causing distant lesion effects. In rats, the favorable effects of epidural placement of Ibo on behavior and on neuronal tissue were compared with and found to contrast with those of kainic acid (KA). Survival periods of 2, 4, 6, and 8 days were allowed for animals of each group. The effects of Ibo from Amanita muscaria were compared to those from Amanita pantherina. Local cortical lesions after epidural placement of KA and Ibo were compared with those after subdural placement. The effects resulting from covering a small surface of the dura with Ibo were compared with those resulting from covering a large surface. Epidural placement of KA and Ibo resulted in neuronal damage of the underlying cortex, 0.4 mg of KA leading to approximately the same lesion extent as 0.5 mg of Ibo. Epidural and subdural lesion effects were found to be similar both for KA and Ibo. The most striking difference between epidural application of KA and Ibo was that KA lesions resulted in a considerable number of damaged areas remote from the local cortical lesion, whereas even 10-times higher doses of Ibo (measured in moles) did not produce any observable neuronal damage outside the local lesion. From these results it is suggested that Ibo has to be favored over KA when local neuronal lesions are desired. Furthermore, epidural placement of Ibo is proposed as an effective technique for producing circumscribed cortical lesions.