Pregabalin suppresses nociceptive behavior and central sensitization in a rat trigeminal neuropathic pain model

Abstract

The aim of this study was to determine whether pregabalin affects nociceptive behavior and central sensitization in a trigeminal neuropathic pain model. A partial infraorbital nerve transection (p-IONX) or sham operation was performed in adult male rats. Nociceptive withdrawal thresholds were tested with von Frey filaments applied to the bilateral vibrissal pads pre- and postoperatively. On postoperative day 7, the behavioral assessment was conducted before and at 30, 60, 120, and 180 minutes after and 24 hours after pregabalin (.1, 1, 10, 100 mg/kg intraperitoneally) or saline injection. The effects of pregabalin or saline were also examined on the mechanoreceptive field and response properties of nociceptive neurons recorded in the medullary dorsal horn at postoperative days 7 to 10. Reduced withdrawal thresholds reflecting bilateral mechanical allodynia were observed in p-IONX rats until postoperative day 28, but not in sham-operated rats. At postoperative day 7, pregabalin significantly and dose-dependently reversed the reduced mechanical withdrawal thresholds in p-IONX rats. Pregabalin also attenuated central sensitization of the neurons, as reflected in reversal of their reduced activation threshold, increased responses to pinch/pressure, and enhanced stimulus-response function. This study provides the first documentation that pregabalin attenuates the mechanical allodynia and central sensitization that characterize this trigeminal neuropathic pain model, and supports its clinical use for treating craniofacial neuropathic pain.

Perspective: Trigeminal nerve injury in rats produced facial mechanical hypersensitivity and trigeminal central sensitization of medullary dorsal horn neurons that were markedly attenuated by systemically administered pregabalin, suggesting its potential clinical utility for orofacial neuropathic pain.

Fig. 1

Time course of the mechanical head withdrawal thresholds after p-IONX in bilateral vibrissal pads. In the sham group (n=6), the threshold did not differ from pre-surgery values in bilateral sides. In the p-IONX group (n=6), bilateral mechanical allodynia was established at the day 1 after surgery. The mechanical allodynia persisted until postoperative days 28 and returned to the level of sham group at 35 days following p-IONX. * p < 0.05 for comparison between the baseline value and values at the different time points after p-IONX (one-way ANOVA). All values shown as mean±SEM.

Fig. 2

Histologically confirmed neuronal recording sites in the p-IONX/pregabalin group (A), the p-IONX/saline group (B), and the sham-operated/pregabalin group (C). The sites were plotted onto a section of the caudal medulla (−5.3 mm behind interaural line). Abbreviations: Sp 5: Trigeminal spinal tract; Vc: trigeminal subnucleus caudalis (MDH: medullary dorsal horn); Dot: WDR neuron; Triangle: NS neuron.

Fig. 3

Examples showing change of central sensitization in NS neurons after Pregabalin (3mg/kg) i.p. to p-IONX group and sham group or saline to p-IONX group. For each example, the pinch RF (top), activation threshold (middle), and responses to pinch/pressure stimuli (bottom) are shown. Data at baseline, 30 min and 60 min after pregabalin or saline injection of each NS neuron are arranged in columns from left to right. Note that the NS neurons illustrated from both the p-IONX/pregabalin and p-IONX/saline groups showed neuroplastic changes at baseline, comparing to sham-operated/pregabalin group. The cutoff (vertical and horizontal) line shows the activation threshold of a given neuron, and the neuronal discharges are displayed in an interspike instantaneous frequency distribution. The unit responses to pinch/pressure stimuli (100g) are also shown in the instantaneous frequency distribution during the 5 s stimulation period. The black area indicates the pinch/pressure RF.

Fig. 4. Changes in mechanical activation threshold and responses to graded mechanical stimuli of NS neurons from p-IONX/pregabalin group, sham-operated/pregabalin group and p-IONX/saline group. Each group consists of eight NS neurons

A. The baseline thresholds of p-IONX/pregabalin group and p-IONX/saline group showed significantly decreases in comparison to sham/pregabalin group. (one-way ANOVA followed by the Bonferroni post-hoc test, p-IONX/pregabalin group vs. sham-operated/pregabalin: p=0.01; p-IONX/saline group vs. sham-operated/pregabalin: p=0.01). In the p-IONX/pregabalin group, pregabalin produced significant increases in threshold during the 60 min observation period (one-way ANOVA followed by Bonferroni post hoc test, baseline vs. 30 min: p=0. 081; baseline vs. 60 min: p=0.007); in the sham/pregabalin group, pregabalin no longer produced increases in thresholds (one-way ANOVA: F=0.10, p=0.91); in the p-IONX/saline group, saline had no effect on mechanical activation threshold of NS neurons (one-way ANOVA:, F=0.64, p=0.54). B. In the p-IONX/pregabalin group, pregabalin significantly decreased the response to pinch at 60 min (one-way ANOVA followed by Bonferroni post hoc test, baseline vs. 30 min: p=0. 002; baseline vs. 60 min: p<0.001); in the sham-operated/pregabalin group, pregabalin produced decrease in pinch response but the decrease was not significant. (one-way ANOVA: F=0.65, p=0.54); saline had no effect on pinch response of NS neurons after p-IONX (one-way ANOVA: F=0.21, p=0.81). All values are shown as mean±SEM.

Fig. 5

Each figure showed the stimulus-responses functions of NS and WDR neurons from 3 groups. Each stimulus-responses function was determined from the neuronal responses to graded mechanical stimuli applied to the neuronal RF. The functions increased significantly after p-IONX. (#: Compared between baselines of p-IONX/pregabalin group or p-IONX/saline group and sham/pregabalin group. Univariate analysis, p-IONX/pregabalin group vs. sham-operated/pregabalin group: p<0.001; p-IONX/saline group vs. sham-operated/pregabalin group: p<0.001). B. In the p-IONX/pregabalin group, the curves of NS neuron stimulus-response function after pregabalin administration shifted downward significantly (Univariate analysis, baseline vs. 30 min: p=0. 003; baseline vs. 60 min: p<0.001), suggesting that pregabalin depressed the response of NS neurons to the stimuli. Note the curves also shifted to the right, which implies an increase of the response threshold. E. The downward shift of the curves in WDR neurons was also significantly (Univariate analysis, baseline vs. 30 min: p=0.002; baseline vs. 60 min: p<0.001). Pregabalin had no significant effect on stimulus-responses function of either NS or WDR neurons in the sham-operated/pregabalin group (A and D). Saline also did not affect the stimulus-responses function of either NS or WDR neurons in the p-IONX/saline group (C and F)

Fig. 6

Changes in responses to graded mechanical stimuli of WDR neurons from p-IONX/pregabalin group, sham/pregabalin group and p-IONX/saline group. Each group consists of eight WDR neurons. In the p-IONX/pregabalin group, pregabalin significantly decreased the response to pinch at 60 min (one-way ANOVA followed by Bonferroni post hoc test, baseline vs. 30 min: p=0.008; baseline vs. 60 min: p=0.002); in the sham-operated/pregabalin group, pregabalin produced decrease in pinch response but the decrease was not significant (one-way ANOVA: F=1.04, p=0.37); saline had no effect on pinch response of WDR neurons after p-IONX (one-way ANOVA: F=0.17, p=0.84). All values are shown as mean±SEM.

Fig. 7

The effects of pregabalin on p-IONX induced mechanical allodynia in bilateral vibrissal pads. On post-operative day 7, the behavioral assessment was conducted before and at 30 min, 60 min, 120 min, 180 min, and 24 hr after injection of pregabalin (0.1, 1, 10, 100 mg/kg i.p., n=6 for each group) or isotonic saline. Pregabalin (1 to 100 mg/kg i.p.) significantly increased the mechanical withdrawal thresholds when compared with saline, while 0.1mg/kg pregabalin had no effect. (Univariate analysis followed by the Bonferroni post-hoc test, ipsilateral: F=73.1, p<0.001; contralateral: F=38.6, p<0.001. post hoc: 1, 10, 100 mg/kg vs saline, p<0.001, 0.1 mg/kg vs saline, p>0.999). All values are shown as mean±SEM.