Gabapentin reverses central pain sensitization following a collagenase-induced intrathalamic hemorrhage in rats

Figures & data

Figure 1 Results from the rotarod test (motor coordination) evaluated in Sprague Dawley® rats.

Notes: Different groups (sham, control, amitriptyline, gabapentin, and carbamazepine) showed no differences (F4, 31=3.29) (nonsignificant). No significant difference was seen between all groups at baseline and at different postsurgical time points (F8, 148=1.92) (nonsignificant).

Figure 2 Results of the mechanical allodynia test using Von Frey filaments.

Notes: Significant differences are seen between the groups, for both hind limbs (right hind limb: F3, 28.1=8.33 [P=0.0004]; left: F3, 28.1=22.68 [P<0.0001]). No significant difference was seen between the baseline values of all the groups. Postsurgery, a significant decrease in the mechanical threshold in both hind limbs was noted for the CTL, AMI, CARBA, and GBP groups (P<0.001). The decrease persisted even after the initiation of treatment (vehicle, AMI, or CARBA) from day 15 to 25, suggesting no significant effect of these drugs on the bilateral mechanical allodynia induced by the collagenase intrathalamic injection when compared with day 11 (P=ns). However, after the initiation of treatment in the GBP group, a reversal of mechanical sensitivity was observed in both hind limbs at all the evaluation times (P=ns, when compared with the CTLs).
Abbreviations: AMI, amitriptyline; CARBA, carbamazepine; CTL, control; GBP, gabapentin; ns, nonsignificant.

Figure 3 Evaluation of cold allodynia with the acetone test.

Notes: Results from the SHAM and CTL groups compared with the amitriptyline (A), gabapentin (B) or carbamazepine (C) groups. The results are presented as the percentage of animals reactive to acetone. Although not statistically significant, the percentage of reactive animals in the CTL group appeared higher than that for the SHAM group. This increase in cold sensitivity returned to baseline at the end of the evaluation period (day 25). When comparing the different treatments (AMI, GBP, and CARBA) with the SHAM and CTL groups, the great variability within and between groups does not allow a clear conclusion.
Abbreviations: AMI, amitriptyline; CARBA, carbamazepine; CTL, control; GBP, gabapentin; SHAM, sham.

Figure 4 Thermal hyperalgesia using the Hargreaves test.

Notes: The results show no difference between the groups (right: F3, 28.2=1.36 [ns]; left: F3, 28.1=1.54 [ns]). For all the groups, there was no significant difference in the thermal thresholds before and after the surgery, in both hind limbs (F8, 131=1.41 [P=ns], F8, 121=1.68 [P=ns]).
Abbreviation: ns, nonsignificant.

Figure 5 Photomicrograph of a transverse rat brain section (4 μm) from the VPL nucleus of the thalamus.

Notes: Following a collagenase solution injection, a well-circumscribed small lesion is present in the thalamus (Hematoxylin and Eosin stain; ×12.5).
Abbreviations: H, hippocampus; T, thalamus; V, ventricle; VPL, ventroposterolateral.