Background Osteoporotic patients with no evidence of fractures sometimes experience vague low back pain. However, there have been few reports regarding the correlation between osteoporosis and pain-related behavior.
Objectives The objective of the current study was to investigate pain-related behavior in osteoporotic mice.
Methods Male ddY mice (8 weeks old) were either hindlimb-unloaded (HU) by tail suspension for 2 Week or hindlimb-loaded (control). The femoral distal metaphyses and the proximal tibial metaphyses (HU group; 12 hindlimbs, control group; 8 hindlimbs) were analyzed three-dimensionally by micro-computed tomography (μCT) 2 weeks after tail suspension. Mechanical sensitivity was tested using von Frey filaments 2 weeks after tail suspension (HU group; 12 hindlimbs, control group; 8 hindlimbs). The frequency of the withdrawal response and the withdrawal threshold to the application of von Frey filaments to the planter surface of the hindpaws was examined. To evaluate the frequency of the withdrawal response, three von Frey filaments with forces of 0.4, 0.6 and 1.4 were applied 5 times each in ascending order of force, and the number and intensity of withdrawal responses were noted. Results were expressed as the percent response frequency of paw withdrawals. To evaluate the withdrawal threshold, each von Frey filament was applied once, starting with 0.008g and increasing until a withdrawal response was reached, which was considered a positive response. The lowest force producing a response was considered the withdrawal threshold.
Results μCT analysis of the distal femoral metaphysis and the proximal tibial metaphysis (Figs. 1, 2) showed that bone volume/tissue volume (BV/TV) and trabecular number (Tb.N) were significantly less in the HU group than in the control group, whereas trabecular separation (Tb.Sp) was significantly greater in the HU group than in the control group. The paw-withdrawal-frequency stimulated by von Frey filaments with strength of 0.4, 0.6 and 1.4 g was significantly higher in the HU group than in the control group (Fig. 3). The withdrawal threshold was significantly lower in the HU group than in the control group (Fig. 4).
Conclusions In this study, hindlimb-unloading induced bone loss and mechanical hyperalgesia in hindlimb. The results suggest that hindlimb-unloaded mouse provides a useful model for osteoporotic pain.
Disclosure of Interest None declared