Ibotenic acid-induced nigral lesion and limbic seizure in cats

The degenerative lesions of bilateral substantia nigra (SN) were made by means of microinjections of ibotenic acid (IBO) solutions and influences upon kainic acid (KA)-induced seizures were studied. IBO solutions were injected bilaterally into SN and circumscribed degenerative lesions were made within the bilateral SN. In a control group, phosphate buffer solutions were injected in the bilateral SN. More than one week after the procedures, 1 μg KA was injected into unilateral amygdala via implanted cannula and limbic seizures were induced. The descruction of SN accelerated the secondary generalization of the limbic seizure within 3 days after the KA injection while no secondary generalization was observed within 3 days in the control group. The fact suggests that GABAergic systems of the substantia nigra and/or ascending norepinephrine pathway have a strong inhibitory influence on the secondary generalization of limbic seizures. The hypothesis of nigral mechanisms as a control system for secondary generalization is discussed.