| Abstrakt: |
Abstract Rationale: Tolerance to delay of gratification, taken to reflect impulsiveness, has been proposed to be under the preferential control of central serotonin (5-HT) processes. Objective: The present study further examined the effects of drugs which directly or indirectly alter 5-HT transmission, on behaviour controlled by a delayed positive reinforcer. Methods: Rats were given the choice in a T-maze between two magnitudes of reward: small (two food pellets) and immediate versus large (ten pellets) but delayed. When a 15-s waiting period was imposed in the arm leading to the large reward, rats selected this arm on 65-70% of the trials. This frequency was reduced to less than 40% when the large reward was delayed by 25 s. Results: In rats whose ascending 5-HT pathways had been lesioned by infusion of 5,7-dihydroxytryptamine (5,7-DHT) into the dorsal raphe, the introduction of the 15-s delay contingency resulted in a transient larger reduction of the frequency of choice of the now-delayed reward, compared to sham operated controls. In contrast, choice behaviour of rats given 5,7DHT into the substantia nigra did not differ from controls, para-Chlorophenylalanine (pCPA, 150 mg/kg IP, daily for 3 days), a 5-HT synthesis inhibitor, bretazenil (0.5-8 mg/kg IP), a benzodiazepine (BZD) receptor partial agonist, and muscimol (0.25-1 rog/kg IP), a GABAA receptor agonist, induced a shift toward immediate reward. In contrast to the other BZDs, alprazolam (1-2 mg/kg IP) enhanced the... [ABSTRACT FROM AUTHOR] |
