Figure 4

Arc/Arg3.1 expression is stimulus intensity dependent and is present only in the acute phase of chronic inflammatory and neuropathic pain. A , Histogram showing the numbers of Arc/Arg3.1 mRNA or c-Fos protein labeled neurons at 2 hours after a brush applied stimulation with either 10% (n = 5) or 50% (n = 5) mustard oil. * = p < 0.05; ** = p < 0.005 (unpaired t-test). B, Time course of Arc/Arg3.1 mRNA and c-Fos protein expression after stimulation with 25% mustard oil gauze wrapped around one hind paw for different survival times. 25 min, n = 4; 45 min, n = 4; 1 h, n = 4; 2 hrs, n = 5; 4 hrs, n = 4; 8 hrs, n = 4. C, Time course of Arc/Arg3.1 mRNA and c-Fos protein expression after CFA injection in the hind paw. 1.5 hrs, n = 4; 3 hrs, n = 4; 4 hrs, n = 4; 10 hrs, n = 4; 20 hrs, n = 4; 60 hrs, n = 4. D, The number of Arc/Arg3.1 mRNA labeled neurons 2 hours after sham operation (n = 3) or after cutting the common peroneal and tibial nerves in the SNI model (n = 3). Error bars represent ± SEM.