Further genetic characterization of the fawn-hooded (FH/Wjd) rat, an animal model of comorbid depression and alcoholism.
OBJECTIVE: The main objective of this study was a more detailed genetic characterization of the alcohol preferring fawn-hooded rat and its intercrosses. Fawn-hooded rats drink substantially more alcohol voluntarily than the ACI rats. The fawn-hooded rats were shown to be more immobile in the forced-swimming test and to drink more saccharin. Recent comparisons of the parental strains with F1 and F2 intercrosses revealed that the alcohol and saccharin intakes were positively correlated with each other but not with immobility. METHODS: The F1 and F2 progeny were generated by intercrossing the fawn-hooded and ACI/N rats. Data from the F2 progeny, their F1 parents and progenitors were used to estimate heritability. RESULTS: Heritability was estimated for alcohol intake (75.6% in males and 67.1% in females), alcohol preference (64.7% in males and 39.2% in females), saccharin intake (50.8% in males and 37.5% in females), and immobility (50.2% in males and 72.1% in females). This same data provided estimates of the number of genes involved in these phenotypes between three and six. We also took advantage of the fact that both progenitor strains are pigmented, so a tremendous variety of coat colors were present in the F2 progeny (i.e. black, black-hooded, agouti, agouti-hooded, fawn, fawn-hooded, orange, and orange-hooded). Coat color analyses indicated that none of the variables significantly varied with coat color. A high correlation however, was observed between alcohol intake and preference in each group. Significant correlations between alcohol and saccharin intakes were seen only in some groups. CONCLUSION: These findings suggest that these phenotypes might be regulated by multiple genes, which could be detected in quantitative trait loci. These analyses are currently underway and will provide a novel approach in understanding the genetics of voluntary alcohol drinking.