The specific aims of this study were to examine with an appropriate experimental design the main and interaction effects of the tranquilizer haloperidol (HPD) and electric shock on head and limb tremors in relation to changes in dopamine (DA) and norepinephrine (NE) concentrations in the caudate nuclei of 36 squirrel monkeys. Head and limb tremors were not observed in 6 control, 6 stress, or monkeys injected (i.m.) with 0.1 mg/kg HPD during 30 days of testing. Transient head and limb tremors lasting from 2 to 4 h after drug injection were observed in 30% of the monkeys of the higher 1.0 mg/kg HPD group. These tremors increased significantly in total incidence from 30 to 50%, and in the extent of the number of extremities affected from 2.8% to 11.1% in the drug-stress interaction group. Thirty days of HPD did not affect DA or NE concentrations in the caudate. Daily electric shock for 30 days decreaed DA but not NE concentrations. Although the 1.0 mg/kg HPD-stress interaction resulted in a higher incidence and extent of tremors, it did not produce a greater decrease in DA than electric shock alone. Since DA concentrations were very high and NE concentrations were low and not affected by drugs or stress, it was concluded that DA may play the more significant role in the caudate of the corpus striatum in primates. © 1969.
