PENTYLENETETRAZOLE AND THIOSEMICARBAZIDE: A STUDY OF CONVULSANT ACTIVITY IN THE ISOLATED CEREBRAL CORTEX PREPARATION

¹ Department of Pharmacology, University of Illinois College of Medicine, Chicago, Illinois

All area of cerebral cortex was completely isolated from the remainder of the nervous system such that the only connection of this isolated plug of cortex with the remainder of the eat was through the pial blood supply.

The isolated cortex was observed to have spontaneous activity characterized by intermittent bursts of spike discharges at a frequency of 45-60 per second. The influence of Metrazol and thiosemicarhazide on the activity of the isolated cortex was studied and compared with the activity produced by these drugs on the intact cortex.

When Metrazol was given intravenously by constant infusion, changes in activity were noted simultaneously in both isolated and intact cortex. However, following intravenous injection of thiosemicarbazide, two or more seizures were recorded on the intact cortex before any changes occurred on the isolated cortex. Both drugs produced spike discharges on the isolated cortex after topical application although there was a latency of 27 minutes with thiosemicarbazide.

In experiments in which both drugs were studied simultaneously, activity typical of Metrazol amid thiosemicarbazide occurred independently on the isolated cortex. These two compounds seemed to be neither additive nor competitive in the isolated cortex.

It was suggested that the site of action of thiosemicarbazide may be initially subcortical in the nervous system of the cat while Metrazol is primarily a cortical convulsant or equally effective at cortical and subcortical levels.