Addiction liability of Tryon rats: independent transmission of morphine and alcohol consumption.

Two inbred strains of Tryon rats were tested for consumption of morphine (0.5 mg/ml) and alcohol (10% w/v) solutions in both free and forced situations. Statistically significant differences in intake by strain were found both for morphine and alcohol. The Tryon S3 strain consumed significantly more morphine than the S1 strain in two of the four phases of the experiment. The Tryon S1 strain consumed significantly more alcohol than the S3 in two of the four phases. Factors affecting consumption of drug solutions including sex and activity level were assessed using analysis of covariance. Strain differences were apparent even when these factors were removed from the analyses. These results are discussed in relation to previous reports suggesting a common addiction liability for both morphine and alcohol in inbred strains of animals.