The Role of GABAergic Projection from Substantia Nigra to Pedunculopontine Nucleus on Kindled Seizures

Abstract

In recent years, there has been great interest in the fact that the substantia nigra (SN) closely regulates the initiation and spread of epileptic motor seizures. However, it has not been elucidated which of the nigral efferent connections can influence the limbic motor seizures. To clarify this question, we studied the role of the GABAergic pathway from SN to pedunculopontine nucleus (PPN) in the amygadaloid seizure of rats. Microinfusions of a GABA antagonist, bicuculline, significantly suppressed the kindled seizures. Next, GABA concentrations in the caudate-putamen (CP), SN, and PPN of kindled rats were determined ty the O-phthalaldehyde method. The GABA concentration was significantly elevated in bilateral PPN, but there were no significant changes in the GABA concentration in CP and SN.
These results indicate that the GABAergic efferent from SN to PPN appears to be involved in the propagation of limbic motor seizures. The GABAergic neuronal activity between SN and PPN may be intensified in the kindling phenomenon, and this may result in the inhibition of the anticonvulsant function of PPN. Thus, the infusion of bicuculline into SN may disinhibit the neuronal activity of PPN and suppress the seizure propagation.