Abstract

Experiments were performed to determine the relative sensitivities of the brains of infant and adult rats to the catecholamine (CA)-depleting actions of two drugs, reserpine and tetrabenazine. CA concentrations in brains of infant and adult animals were determined at various times after reserpine (0.1 mg/kg), 1 hr after tetrabenazine (1 and 2 mg/ kg), 18 to 24 hr after reserpine (0.025—1.5 mg/kg) and during and after 20 daily injections of reserpine (0.1 mg/kg). A single dose of 0.1 mg/kg of reserpinereduced CA concentrations more rapidly, to a greater extent and for a longer time in infantthan in adult rats. One hour after administration of tetrabenazine there was a greaterdepletion of CA in the brains of infant than in the brains of adult animals. Curves relatingCA depletion in the brain to dose of reserpine indicate that sensitivity of the brain to thedepleting action of reserpine gradually decreased as the age increased, infants being mostsensitive, weanlings less so and adults least sensitive. On repeated daily administration of 0.1 mg/kg of reserpine, maximal depletion occurred at a slower rate in adults than in infants. Rates of repletion of catecholamines following the cessation of repeated administration appeared comparable in infant and adult animals. These findings indicate that the brains of infant rats are more sensitive than those of adults to the CA-depleting actions of both reserpine and tetrabenazine.