This image shows indirect pathway axons (green) and enkephalin (magenta) in the mouse external pallidum. Direct pathway axons innervate Npas1⁺ pallidal neurons and are strengthened in a chronic model of Parkinson's disease. This contrasts with indirect pathway axons that innervate PV⁺ pallidal neurons and are unchanged. For more information, see the article by Cui et al. (pages 3966–3987). Image credit: Qiaoling Cui.