Brain gene expression levels of Penk (encoding preproenkephalin) and Foxp1 (encoding forkhead box P1). The signal intensities of two genes, Penk and Foxp1, were imported into the NeuroZoom software tool to visualize the three-dimensional gene expression patterns of these genes in the context of brain anatomy. A ratio of the signal intensities of (a) Penk and (b) Foxp1 between 129S6/SvEvTac (129) and A/J (A) strains is shown in hippocampus (Hi), hypothalamus (Hyp), periaqueductal gray (PAG), and bed nucleus of the stria terminalis (BNST). The expression fold change values are shown in the upper right corner of each panel for each brain region separately, together with color coding that matches the color of each brain region in the three-dimensional mouse brain atlas, shown from four different angles. Note that the gene expression level of Penk in Hi and Hyp is higher in the 129 strain than in the A strain, but in Pag and Bnst it is higher in the A strain than in the 129 strain. Similarly, the expression level of Foxp1 in Hi is higher in the 129 strain than in the A strain, whereas in Hyp, Bnst, and Pag the expression level is higher in the A strain than in the 129 strain.