Alteration of electroconvulsive threshold by cerebrospinal fluid from cats tolerant to electroconvulsive shock

Daily electroconvulsive shocks for 22 days resulted in a progressive elevation of electroconvulsive threshold. When these shocks were discontinued, the thresholds returned to untreated levels in approximately 20 days. Cerebrospinal fluid collected from cats with elevated thresholds and repeatedly transferred to the ventricular space of untreated animals elevated the electroconvulsive threshold of the recipient. This finding demonstrates that a substance present in the cerebrospinal fluid of cats with elevated electroconvulsive threshold can alter the threshold of untreated animals.