Resumo

BALDERRAMA-TRAPAGA, JORGE ARTURO  e  APARICIO-NARANJO, CARLOS FERNANDO. Effects of Dopamine Agonists and Antagonists in Variable Reinforcing Environments. Univ. Psychol. [online]. 2008, vol.7, n.2, pp.507-533. ISSN 1657-9267.

The anhedonia hypothesis maintains that pleasure for food-reward is determined by dopamine activity in the brain. The cumulative body of empirical evidence shows that dopamine agonists and antagonists (e.g., Methylphenidate and Haloperidol, respectively) decrease operant behavior maintained by positive reinforcement. The present study used the generalized matching law (Baum, 1974) to assess effects of these drugs on the motor system and the organism's motivation for food reinforcers. Thirty-two rats searched for food in a choice situation where the reinforcer ratio provided by two alternatives changed everyday. The results confirmed that the drugs do not impede the rats' rapid adaptation to dynamic changes in the contingencies of reinforcement. Preference favored with more responses the alternative associated to the higher probability of reinforcement, showing an increment in sensitivity of behavior ratio to changes in food ratios. The alternative demanding the higher motor requirement showed a decrement in the number of responses, suggesting effects of the drugs in the organism's motor system.

Palavras-chave : Methylphenidate; Haloperidol; Choice; Motivation; Reinforcement; Rats; Laboratory Research; Dopamine; Dopamine Agonists; Dopamine Antagonists.

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