Rat Brain Gene Expression (IMAGE) Michigan Medicine - University of Michigan Caption In these images of rat brains, differences in gene expression of genes for fibroblast growth factor 2 (FGF2, top set) and dopamine 2 receptor (D2, bottom sett) can be seen in rats of two breeds before (left) and after (right) cocaine exposure. The addiction-prone bHR rats differed significantly in several ways from the timid bLR rats. Credit Flagel Lab, University of Michigan Usage Restrictions Credit University of Michigan License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.