Calcium deposits develop in rat substantia nigra but not striatum several weeks after local ibotenic acid injection

The excitotoxin ibotenic acid (IBO) was used to place local circumscript lesions in rat substantia nigra (SN). Four to six months after the injection we found in the neuron depleted SN basophilic deposits resembling calcium concretion. Additional experiments revealed that calcium deposits, as verified with the alizarin red stain, were first detectable after a delay of 4 weeks. They increased in number, size and extent over the following 12 weeks, but remained confined to the boundaries of SN. Injection of at least 3.5 micrograms IBO was necessary for induction of deposits. In striatum, 14 micrograms IBO did not cause clearly identifiable concretions. Thus, IBO-induced lesions are not stationary but mature, and the long-term effects can be different in different brain regions. These observations may have some relevance for considerations on the cause of the idiopathic nonarteriosclerotic calcifications.