FGFR1 and FGF4 mRNAs are up-regulated in muscle undergoing disuse atrophy. FGFR1 and FGF4 mRNAs were analyzed in sections of gastrocnemius muscle obtained from control mice or mice suspended for 4 or 7 days by in situ hybridization. In comparison to controls, FGFR1 and FGF4 mRNA signal, as depicted by white silver grains in dark field images, were upregulated in gastrocnemius muscles suspended for 4 days (A). Direct dpm analyses were obtained using the Cyclone Storage Phosphor System, and FGFR1 and FGF4 mRNA levels were found to be significantly greater in muscles suspended for 4 days than control muscle or muscle suspended for 7 days. Dotted lines represent the outline of the gastrocnemius muscles. SEM indicated over control; means with different superscripts differ p < .05; n = 10 for each mean.