Functional anatomy of pentylenetetrazol and electroshock seizures in the rat brainstem

The ability of discrete brainstem injections of gamma-vinyl-gamma-aminobutyric acid (GVG), an irreversible inhibitor of gamma-aminobutyric acid transaminase, to prevent pentylenetetrazol (PTZ) seizures and maximal electroshock seizures (MES) was studied and compared in rats. PTZ seizures were prevented by GVG injections in the anterior thalamus, the caudal hypothalamus, the superior colliculus, cerebellar nuclei, and in a large area of the medial medullary, pontine, and mesencephalic tegmentum encompassing the vestibular nuclei, the reticular formation, and portions of the central gray. GVG injections in the substantia nigra did not protect against PTZ seizures. In contrast, tonic hindlimb extension in MES was prevented consistently by injections in the substantia nigra. A minority of injections in the vestibular nuclei, cerebellar nuclei, and parts of the reticular formation also protected against tonic hindlimb extension of MES. These results indicate a striking difference in the functional anatomy of PTZ-induced seizures and MES. PTZ seizures appear to be mediated by an extensive system involving the reticular formation, diencephalic regions in the vicinity of the anterior medial thalamus and caudal hypothalamus, and bulbar regions which give rise to descending motor pathways to the spinal cord. In contrast to PTZ seizures, MES appears to be mediated by a different neuroanatomical substrate with the present data implicating only the substantia nigra definitely in that process.