Fig 3. Higher i.c.v. [Na⁺] causes nociception.

(A) The aversive threshold response to von Frey hairs was measured in both hindpaws after i.c.v. treatment with aCSF containing either 250 mM sodium (n = 14; circle) or aCSF with 150 mM [Na⁺] that was osmotically-matched to the 250 mM [Na⁺] by addition of sucrose (n = 11; square). (B) The eyelid closure was measured before and at 20 minutes after pre-treatment with i.c.v. 150 mM or 250 mM [Na⁺]. Means (SEM) displayed, n = 3 rats per i.c.v. treatment group. (C) Unilateral i.c.v. infusion of aCSF with 250 mM [Na⁺] compared to osmotically matched 150 mM [Na⁺] had increased cFos expression in the TNC. (D) Representative photomicrographs delineating the cFos response in the 150mM and 250 mM [Na⁺]-infused rats. Scale bar = 200 μm. (150 mM n = 10; 250 mM = 14). * = p < 0.05; ** = p < 0.01; *** = p < 0.001.