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L-Tryptophan decreases the breaking point under a progressive ratio schedule of intravenous cocaine reinforcement in the rat

1993; Elsevier BV; Volume: 44; Issue: 3 Linguagem: Inglês

10.1016/0091-3057(93)90181-r

1873-5177

Alison McGregor, Susan Lacosta, David C. S. Roberts,

Tryptophan and brain disorders

l-Tryptophan (100 mg/kg, IP), the serotonin [5-hydroxytryptamine (5-HT)] amino acid precursor, significantly reduced the mean breaking point maintained under a self-administration progressive ratio schedule of IV cocaine reinforcement (0.6 mg/injection). This effect was produced over the 5 days of self-administration following treatment. Responding maintained under the same progressive ratio schedule for food reinforcement was not affected by l-tryptophan (100 mg/kg, IP). Rats administered l-tryptophan (100 mg/kg, IP) and denied access to cocaine on the day of treatment resumed normal self-administration patterns under a progressive ration schedule on following test days. This indicates that l-tryptophan treatment alone did not induce long-term effects on cocaine self-adminisration. Thus, it would appear that the combination of this 5-HT manipulation and cocaine administration altered the reinforcing efficacy of the drug and induced a long-term decrement in breaking point under a progressive ration schedule. This may have been due to an associative aversion to cocaine self-administration behaviour learned on the day of treatment and carried over to the subsequent 5 days of self-administration access.