English: This is a protein-protein interaction network showing the relationship between proteins associated with Heroin Use Disorder (HUD). It was constructed using the Search Tool for the Retrieval of Interacting Genes/Proteins database (STRING v10.5). Given a list of proteins as input, the STRING tool can search for the "neighbor interactors", or proteins that directly interact with the proteins given. This list was then used to generate the protein-protein interaction network pictured here. After this, the team further searched through lab experiments, curated databases, and gene expression data to construct a new network, with the same level of confidence as the previous PPI, for comparison (See Figure S1 in source article). Each node is a protein, and the edges show their relations. Within the network there are 111 nodes and 443 edges. 16 of the proteins, represented by the nodes, demonstrate large degree centrality or high measures of betweenness centrality (described in methods section); thereby, they are highly integral to the network, serving as the backbone. According to the authors, the PCK1 protein has the highest betweenness centrality and MAPK14 has the second largest degree centrality as well as the 9th highest betweenness, leading them to believe that these two proteins are involved with the development in HUD as well as other substance use diseases.