Brain biogenic amines and intravenous self-administration of cocaine in rats

1. The possible involvent of noradrenaline, dopamine, serotonin and 5-hydorxyindoleacetic acid in the behavioural reinforcement produced by invravenous cocaine has been investigated. 2. rats, in Skinner boxes, were allowed to self-administer cocaine through a chronically implanted jugular vein cannula. A consistent response rate in the order of one self-administration every 10 min was observed with a dose of 3.0 mg/kg cocaine hydrochloride per response. 3. Another group of rats was cannulated and injected with a range of one to six such doses of cocaine at 10 min intervals on the basis of the responding rate, established by rats in the Skinner box. At times of 2,5 and 8 min after each dose of cocaine, the rats were decapitated and brain concentrations of noradrenaline, dopamine, serotonin and 5-hydroxyindoleacetic acid were determined. 4. The brain levels of noradernaline exhibited a cyclic pattern of rise and fall after each dose of cocaine, which corresponded in its time base with the time interval between responses established by the rats in the Skinner box.