Effects of various drugs on activity of the neuronally isolated cerebral cortex.

The topical application of strychnine, d-tubocurarine, pentylenetetrazole, picrotoxin, and physostigmine evoked different patterns of electrical activity in a portion of the acutely isolated suprasylvian gyrus of dogs. Pentylenetetrazole and picrotoxin evoked a similar pattern of activity in the isolated gyrus by both topical application and intravenous administration. Reasonable systemic doses of strychnine, d-tubocurarine and physostigmine did not produce activity similar to that seen on topical application. Therefore, the effects obtained by topical application of drugs to the cerebral cortex must be interpreted cautiously as regarding the usual pharmacological actions of these agents. Adrenergic agents, administered systemically, exerted a diphasic effect upon chemically and electrically evoked activity. An initial depression and subsequent enhancement were observed. These actions were exceedingly variable and did not appear to be secondary to vascular effects. On the other hand the effects of acetylcholine and arecoline did seem to be secondary to their cardiovascular effects. Since entirely different patterns of spontaneous and evoked electrical activity could be recorded simultaneously from the isolated and nearby intact portions of the cortex, it was concluded that the neuronally isolated cerebral cortex gave rise to independent activity.