Article Figures & Data
Figures
- Figure 1.
Activation of serotonergic afferents in spinal cord is aversive. A, Immunohistochemical verification of ChR/eYFP expression (green) in serotonin-expressing neurons (red) in RVM. B, In vitro verification that trains of optical stimuli (20 Hz) can entrain ChR expressing neurons in RVM. Scale bar = 20 mV/200 ms. C, Optical stimulation (4 repetitions of 10 pulses, 4-ms durations, at 20 Hz with 10 s between trains) of spinal serotonergic afferents that express channelrhodpsin produces mechanical allodynia in naive mice (blue) but not in animals expressing eGFP (black). D, Optical stimulation of spinal 5HT axons evokes conditioned place avoidance only in mice that express ChR and not eGFP controls. **p < 0.01, repeated measures ANOVA in C and paired t test in D. N = 5 per group.
- Figure 2.
Phasic release of serotonin in SpVc is unaffected by CFA-induced inflammatory pain. A, CFA-induced inflammation reduces withdrawal thresholds to mechanical stimulation of the orofacial region. B, Changes in fluorescence of a serotonin sensor expressed in SpVc and measured by fiber photometry in response to noxious pinch. The heatmap shows the sensor response to 10 consecutive pinches with the average and 95% confidence intervals of all 10 responses depicted in the trace below. In vitro verification of the sensor response to exogenous application of 50 and 100 μm serotonin (thin and thick blue lines) is shown in the inset. C, Average of pinch (t = 0) evoked serotonin transients in SpVc from naive mice and from mice 3–5 d after CFA injection (n = 5 per group). There is no difference in the response, measured as area under the curve (AUC), between sham and CFA mice (D). p > 0.05, t test. ****p < 0.0001.
- Figure 3.
Tonic serotonin levels are elevated in SpVc in a mouse model of neuropathic pain. A, CCI-ION reduces withdrawal thresholds to mechanical stimulation of the orofacial region. B, Concentrations of serotonin in isolated SpVc tissue were quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Group sizes: n = 9 sham and n = 11 CCI, p = 0.018, unpaired t test. *p < 0.05, ****p < 0.0001.
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