Specific action of tranylcypromine to precipitate barbital withdrawal convulsions.

This research was designed to determine whether the convulsion-eliciting action of tranylcypromine (TCP) during bartibal (B) withdrawal was specific to physical dependence on B, and to compare the findings with the action of pentetrazol (PTZ). Challenge with 15-20 mg/kg IP TCP at 48 or B withdrawal resulted in the elicitation of clonic-tonic convulsion (CTC) in all rats (n = 6) within 10 min. Another challenge with 5-20 mg/kg TCP led to the dose-related precipitation and intensification of CTC. The CTC-inducing action of TCP was relatively reduced as the B withdrawal signs were gradually mitigated. In other words, when challenge with the drug was made at 72h of B withdrawal, the time of CTC onset was prolonged, and the incidence was reduced to 50% in parallel with abolition of the other withdrawal signs. A challenge at 120 h of B withdrawal when the vital signs had almost recovered to prewithdrawal level failed to induce even the prodromal signs of convulsion. In all rats exhibiting only mild to moderate withdrawal signs (such as hyperirritability, hyper-reflexia, anorexia, weight loss), 40 mg/kg TCP was required to induce CTC during B withdrawal, which was twice the dose required in severely dependent rats. Other monoamine oxidase inhibitors, i.e., pargyline, iproniazid, and clorgyline, elicited no CTC during B withdrawal. Methamphetamine was without effect on B withdrawal convulsions. From these findings, the convulsive threshold for TCP during B withdrawal proved well correlated to the grade of B-dependence and the duration of B-withdrawal signs.