A METHOD TO BIOTINYLATE AND HISTOCHEMICALLY VISUALIZE IBOTENIC ACID FOR PHARMACOLOGICAL INACTIVATION STUDIES

Ibotenic acid (IA) and kainic acid (KA) are commonly used tools to sel ectively inactivate neuronal perikarya, eventually leading to their de generation, without affecting fibers of passage. Reversible inactivati ons and experimental paradigms that do not allow for long survival tim es, however, do not permit for histological verification of the site a nd extent of the lesion by identifying the area showing gliosis. We de scribe here a method in which IA and KA were conjugated with biotin an d thus could be easily visualized histochemically. We pressure-injecte d biotinylated IA and KA into various hindbrain areas of the electrose nsory system in electric fish while monitoring neuronal responses at t he injection site and assessing effects on the behavior. Whereas the e ffects of biotinylated IA did not differ from those of the unbiotinyla ted form, biotinylated KA lost its physiological activity. Thus, only biotinylated IA could be used successfully. The size of the gliosis se en after a survival time of seven days was similar to the extent of bi otin label observed after injection of comparable volumes of biotinyla ted IA. Moreover, this method resulted in labeling of individual neuro ns presumably affected by IA and yielded information about their proje ction patterns which was comparable to labeling seen after intracellul ar injections of neurobiotin or biocytin. (C) 1997 Elsevier Science B. V.