Cover legend:A coronal slice of mouse hippocampus that was cultured in vitro for 14 d. GFP (green) marks all interneurons expressing glutamic acid decarboxylase 67 (GAD67). Staining against parvalbumin is red and nuclei are labeled with DAPI (blue). Activity deprivation for 2 d with tetrodotoxin reduces the expression of GAD67 and GFP reporter. For more information, see the article by Lau and Murthy (pages 8521–8531).