Monoamine oxidase inhibition: effect on 5-hydroxytryptamine output from perfused third ventricle and body temperature.

1. In cats anaesthetized with pentobarbitone sodium the third ventricle was perfused with artificial c.s.f., the effluent was collected in 30 min samples and assayed for 5-hydroxytryptamine (5-HT) on the rat stomach-strip preparation. Rectal temperature was monitored continuously.2. On perfusion of artificial c.s.f. through the third ventricle, small amounts of 5-HT appeared in the effluent; the amounts decreased with successive samples.3. When tranylcypromine (Parnate), an inhibitor of amine oxidase, was added to the perfusion fluid and perfusion was continued, the 5-HT output increased. This increase was associated with shivering and a rise in temperature which was not, however, maintained.4. When tranylcypromine was injected intraperitoneally, during the fall in temperature produced by the pentobarbitone sodium anaesthesia, the 5-HT output also increased, shivering occurred and the fall in temperature was halted or reversed. The effect on temperature was maintained.5. When the cat was killed and perfusion was continued, the 5-HT output, already elevated by the tranylcypromine before death, increased even further in the next few samples.