Spontaneous and amphetamine induced head-shaking in infant rats.

A variable proportion of albino rats 6-11 days old exhibit spontaneous and infrequent rotatory head-shaking episodes. This motor pattern is slightly anticipated and significantly increased in occurrence and duration by the administration of D-amphetamine (5 mg/Kg), with a maximal effect of the drug on the 9th day. The rate of amphetamine induced rhythmic head oscillations increases with age from below 5 cps on the 5th day to about 9 cps on the 10th day. The results are discussed in relation to maturation of both the underlying catecholaminergic pathways, activated by D-amphetamine, and the stretch reflex systems of the head and neck muscles participating in the rhythmic activity. Emphasis is placed on the difference between head-shaking and stereotyped activity.