Abstract

Rats were trained to climb a vertical rope. The time required for climbing was noted, as well as the behavior of the animals. In general, antihistaminic drugs produced muscular incoordination and evidences of cerebral depression in the trained animals, resulting in prolongation of the climbing time, or even complete failure. Curare also prolonged the climbing time, but the effect appeared to be due to muscular weakness and fatigue, in contrast to the confusion and incoordination observed in the animals treated with antihistaminic drugs.

The various antihistaminic drugs differed widely in their tendency to produce the effect described, but the order of relative effectiveness was different from that previously found in the potentiation of the hypnotic action of barbiturates in mice. It is therefore suggested that the two types of experiments demonstrate actions upon different areas of the higher centers.

Amphetamine and caffeine counteract the depressant effect of the antihistaminic drugs as evidenced in the climbing test, while cocaine and Picrotoxin add to the confusion of the animals and to the delay in climbing. Alcohol neither increased nor decreased the effect.

Phenindamine (Thephorin) differed from the other antihistaminic drugs studied in that it produced evidence of central excitation rather than depression. Amphetamine and caffeine increased this effect of phenindamine. On the other hand, phenindamine potentiated the effect of a depressant drug (Phenergan) on the performance of the animals.