LESIONS OF CENTRAL SEROTONIN SYSTEMS AFFECT RESPONDING ON A PROGRESSIVE RATIO SCHEDULE REINFORCED EITHER BY INTRAVENOUS COCAINE OR BY FOOD

The effect of intraventricular infusions of the serotonergic neurotoxi n, 5,7-dihydroxytryptamine (5,7-DHT), was examined in rats trained on a progressive ratio schedule for either IV cocaine or food reinforceme nt. Animals in the 5,7-DHT treatment group responded to significantly higher breaking points than vehicle-injected control animals, regardle ss of whether food or cocaine was used as the reinforcing stimulus. An alysis of the regional brain amines indicated that depletions of mesen cephalic 5-HT correlated with postsurgical alterations in responding. These findings suggest that depletion of forebrain 5-HT produces a gen eral effect on responding rather than a specific alteration in the rei nforcing effects of psychomotor stimulant drugs.