Fig. 3.

Right-hemispheric lateralization of arthritis pain-related changes. A: unchanged background and evoked activity of 1 left CeLC neuron in arthritis. B: increased background and evoked activity of 1 right CeLC neuron after arthritis induction. A and B: line graphs show the time course of extracellularly recorded responses (number of spikes per second) to brief (15 s) innocuous (500 g/30 mm²) and noxious (2,000 g/30 mm²) stimulation of the knee and background activity. Symbols show the mean activity during a 15-s period before stimulation (= background activity) or the difference between mean activity during and before 15-s stimuli (= net activity evoked by noxious or innocuous stimuli; see methods). Peristimulus time histograms (insets) show individual responses (spikes per second) before and 5 h after induction of arthritis. Top traces show recordings of the force (g/30 mm²) applied to the knee joint with a calibrated forceps (see methods). C: comparison of left vs. right CeLC neurons. Under normal conditions before arthritis, there was no significant difference of background and evoked activity between left (n = 11) and right (n = 9) CeLC neurons (P > 0.05, Tukey test). Five hours after arthritis induction, activity of right CeLC neurons was significantly higher than that of left CeLC neurons (P < 0.01–0.05, Tukey test). Bar histograms show background activity and responses to innocuous (500 g/30 mm²) and noxious (2,000 g/30 mm²) stimulation of the knee averaged for the sample of neurons (means ± SE). Single asterisk, P < 0.05; double asterisks, P < 0.01 (Tukey test, comparing values in right vs. left CeLC neurons).