Psychopharmacology

, Volume 118, Issue 4, pp 437–443

Bromocriptine enhancement of responding for conditioned reward depends on intact D1 receptor function

  • R. Ranaldi
  • R. J. Beninger
Original Investigation

DOI: 10.1007/BF02245944

Cite this article as:
Ranaldi, R. & Beninger, R.J. Psychopharmacology (1995) 118: 437. doi:10.1007/BF02245944

Abstract

It has been suggested that reward-related learning may require intact functioning at the dopamine D1 receptor. The present experiment tested this hypothesis by challenging the reward-enhancing effects of the D2 agonist, bromocriptine, with a D1 antagonist, SCH 23390. For comparison, the effects of the D2 antagonist, pimozide, were also evaluated. Male rats (n=240) were pre-exposed to a chamber with two levers, one producing a 3-s lights-off stimulus and the other a 3-s tone stimulus. Four conditioning sessions followed, during which levers were absent and presentations of the lights-off stimulus were paired with food. Testing consisted of comparing presses on each lever after conditioning to before conditioning for each rat. Control groups showed a significantly greater increase in responding for lights-off than tone, indicating that the lights-off stimulus had become a conditioned reward. Results showed that bromocriptine (0.25–10.0 mg/kg, IP, 60 min before test session) enhanced responding at doses of 2.5 and 5.0 mg/kg significantly more on the conditioned reward lever than on the other lever. The lowest dose of SCH 23390 (1.0 µg/kg, SC, 2 h before testing) eliminated the bromocriptine-produced enhancement at 2.5 mg/kg and a significant enhancement was seen at 10.0 mg/kg. The higher doses of SCH 23390 (5.0 and 10.0 µg/kg) eliminated the bromocriptine effect and the conditioned reward effect itself, respectively. The low dose of pimozide (0.1 mg/kg, IP, 4 h before test session) eliminated the bromocriptine-produced enhancement at 2.5 and 5.0 mg/kg and a significant enhancement was now seen at 10.0 mg/kg; the higher dose (0.2 mg/kg) appeared to block the conditioned reward effect itself. These results suggest that both SCH 23390 and pimozide interfered with the reward-enhancing effects of bromocriptine. Thus, the present results suggest that reward-related learning can be enhanced through D2 receptor stimulation with bromocriptine and that this effect appears to depend on intact D1 receptor function.

Key words

Bromocriptine Conditioned reward D1 receptors D2 receptors Dopamine Reinforcement Reward SCH 23390 

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Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • R. Ranaldi
    • 1
  • R. J. Beninger
    • 1
  1. 1.Department of PsychologyQueen's UniversityKingstonCanada
  2. 2.Life Sciences Research CenterCarleton UniversityOttawaCanada

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