Behavioural sensitization to a dopamine agonist is associated with reversal of stress-induced anhedonia |
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Authors: | Mariusz Papp Paul Willner Richard Muscat |
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Institution: | (1) Department of Psychology, City of London Polytechnic, Old Castle Street, El 7NT London, UK;(2) Present address: Institute of Pharmacology, Polish Academy of Sciences, Krakow, Poland;(3) Present address: Department of Biomedical Sciences, University of Malta, Msida, Malta |
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Abstract: | Chronic exposure to very mild unpredictable stress (CMS) has previously been found to reduce the consumption of palatable sweet solutions and to impair place preference conditioning; evidence has been presented that these effects may reflect a dysfunction of the mesolimbic dopamine system. In the present study, rats were subjected to CMS for a total of 9 weeks. CMS reduced the consumption of a 1% sucrose solution. During weeks 6 and 7, animals received quinpirole (0–400 µg/kg) twice weekly. Both CMS-treated animals and controls showed sensitization to the locomotor stimulant effects of quinpirole. Subsequently, a sustained recovery of sucrose drinking was observed in quinpirole-treated stressed animals. During week 8, all animals received a single pair of place preference conditioning trials, in which quinpirole (200 µg/kg) was administered in a distinctive environment, and vehicle in a different environment. Non-stressed animals showed an increase in preference for the environment associated with quinpirole, as did stressed animals that had been sensitized to quinpirole; this effect was absent in untreated stressed animals. Finally, in week 9, acute administration of raclopride (150 µg/kg) was found to reverse the recovery of sucrose drinking in quinpirole-treated stressed animals, suggesting that these effects are mediated by an increase in dopamine function. |
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Keywords: | Stress Sucrose consumption Place preference conditioning Reward Quinpirole Behavioural sensitization Dopamine Rats |
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