Mechanism of action of thiosemicarbazide and Metrazol on cerebellar and cerebral activity in the cat

¹ Departments of Anatomy and Physiology, School of Medicine, University of California, Los Angeles; and Veterans Administration Hospitals, Sawtelle and Long Beach, California

Neocortical wave activity during thiosemicarbazide (TSC) induced seizures was less regular and lower in amplitude than cerebellar wave activity. The regular progression of slow activity seen with TSC in successive seizures was not encountered with Metrazol. Following TSC injection, dendritic and subcellular d.c. potential gradients became increasingly negative up to the first seizure discharge. Following the first seizure discharge the d.c. level decreased in negativity. Examination of the neocortical d.c. gradient after TSC injection failed to reveal a predictable and sustained shift. Purkinje and cortical cells which had responded to repetitive sciatic stimulation became inaccessible to such stimulation following TSC injection and the positive phase of individual cells decreased about 30% in amplitude and almost doubled in duration. Pyridoxine hydrochloride gradually arrested TSC induced seizures. Metrazol had little effect on the cerebellar and neocortical d.c. gradients and unit action potentials. Following TSC injection, thresholds for both hyperpolarization and depolarization effects observed in the cerebellar cortex were markedly raised.