Digigait quantitation of gait dynamics in rat rheumatoid arthritis model

INTRODUCTION

Rheumatoid arthritis (RA) is characterized by joint pain, allodynia and hyperalgesia. The rat carrageenan model utilizes inflammation-associated pain following injection of the knee joint to model RA. Traditional assessment of pain in these models utilizes behavioral scoring or manual measurements, methods that are labor intensive and prone to subjective interpretation. This study utilizes the Digigait system to objectively quantify movement and gait dynamics in a monoarthritic rat model.

MATERIAL AND METHODS

A pilot study in rats selected "natural" runners using Digigait, and also measured inter and intraday variability as well as effects of anesthesia on gait dynamics. In the main study, 12 female rats were tested at baseline, divided in two groups of 6 rats, briefly anesthetized with isoflurane and injected with 60 microl of 2% lambda carrageenan or vehicle; Digigait testing was repeated 2 and 4 hours post injection and data analyzed.

RESULTS

Selection of "natural" runners significantly contributed to accuracy and reproducibility of gait parameters obtained by the Digigait system. There was minimal intra and inter day variation between individual rats and 4 minutes of isoflurane anesthesia had no effect on gait dynamic at 2 and 4 hours post administration. In the main study a highly reproducible gait signature in the injected limb, and well coordinated adaptation of gait during locomotion in the non-affected limbs were noted as short-term changes following carrageenan injection.

CONCLUSION

Digigait system was found to be an objective and reliable method for quantification of early behavioral changes consistent with allodynia and hyperalgesia in an inflammatory pain model.

Bone parameters are improved with intermittent dosing of vitamin D3 and calcitonin

Intermittent combination of an anabolic agent to promote bone formation and an antiresorptive agent that would prevent further bone loss is a theoretically attractive approach for restoring bone mass. We tested the potential of intermittently dosed calcitriol and calcitonin (CT) to restore bone properties in ovariectomized (Ovx) rats. Rats had Ovx or sham surgery at 8 weeks old and 4 weeks later were assigned to experimental groups: (1) sham vehicle, (2) Ovx vehicle, (3) Ovx + parathyroid hormone (PTH, 40 microg/kg), and (4) Ovx + calcitriol (2 microg/kg) + CT (2 microg/kg). Group 3 received PTH every week throughout the study, and group 4 received calcitriol at weeks 1, 3, 5, and 7 and CT at weeks 2, 4, 6, and 8. Dosing was carried out for 8 weeks with serum, and micro-computed tomographic analysis was done at 0, 4, and 8 weeks. Femurs and tibias were used for radiological analyses and for mechanical testing. Dosing with PTH improved bone mass and structure of cancellous bone at metaphyses of tibias and femurs as well as properties of cortical bone including geometry and strength. Intermittent dosing with calcitriol and CT was less potent in correcting loss of cancellous bone relative to treatment with PTH and had no effect on cortical bone parameters. However, intermittent dosing with calcitriol and CT was robust enough to improve cancellous bone mass and structure through bone formation without causing deleterious side effects. Our data provide additional evidence that therapies can be devised to ameliorate the skeletal defects associated with established osteoporosis.