Use of 6-hydroxydopamine to deplete brain catecholamines in the rhesus monkey: effects on urinary catecholamine metabolites and behavior.

The purpose of this study was to determine: 1) whether 6-hydroxydopamine (6-OHDA), previously shown to deplete brain catecholamines (CA) in rodents, depletes brain CA in rhesus monkeys; 2) whether depletion of brain CA produces changes in behavior; and, 3) whether urinary output of 3-methoxy-4-hydroxyphenylglycol (MHPG) reflects brain norepinephrine (NE) depletions. Repeated intracerebroventricular (ICV) injection of 6-OHDA (N = 20; 15.5-73.3 mg/subject) produced chronic changes in social behavior and, at higher dosages, reduced output of urinary MHPG. However, 4 weeks after the last ICV 6-OHDA injection, urinary MHPG excretion returned to baseline values and whole brain CA content was not reliably different from control. A single treatment with 6-OHDA microinjected into the substantia nigra (SN) (N = 12; 120-240 microgram/subject) produced chronic whole brain depletions of brain CA without depleting serotonin. Reductions in brain CA were associated with a specific set of motor behaviors, aphagia, and adipsia. SN 6-OHDA produced greater brain NE depletions than ICV 6-OHDA, but urinary MHPG output was not reduced. SN 6-OHDA treated subjects showed chronic changes in social behavior and were more sensitive to the operant response rate decreasing effects of alpha-methyl-para-tyrosine (AMPT) than control subjects. Subjects with the largest depletions of brain dopamine (DA) (greater than 90%) were hypokinetic, rigid, and had a distal limb tremor. These results show that SN but not ICV injection of 6-OHDA can deplete brain CA in the rhesus monkey. The most prominent behavioral changes were characterized by disturbances in motor function. Urinary MPHG output does not reflect depletions of brain NE in this species.