Bone Structural, Biomechanical and Histomorphometric Characteristics of the Postcranial Skeleton of the Marsh Rice Rat (Oryzomys palustris)

Abstract

INTRODUCTION: The rice rat (Oryzomys palustris) is a non-conventional laboratory rodent species used to model some human bone disorders. However, no studies have been conducted to characterize the postcranial skeleton. Therefore, we aimed to investigate age- and gender-related features of the appendicular skeleton of this species. METHODS: We used femurs and tibiae from 94 rats of both genders aged 4-28 wks. Bone mineral content (BMC), bone mineral density (BMD), and biomechanical properties were determined in femurs. In addition, bone histomorphometry of tibiae was conducted to assess bone cells activities and bone turnover over time. RESULTS: Bodyweight, bone length, total metaphysis BMC/BMD, cortical BMC/BMD, cortical thickness, and cortical area progressively augmented with age. Whereas the increase in these parameters plateaued at age 16-22 wks in female rats, they continued to rise to age 28 wks in male rats. Furthermore, bone strength parameters increased with age, with few differences between genders. We also observed a rapid decrease in longitudinal growth between ages 4-16 wks. Whereas young rats had a greater bone formation rate and bone turnover, older rice rats had greater bone volume and trabecular thickness, with no differences between genders. CONCLUSIONS: 1) Sexual dimorphism in the rice rat becomes grossly evident at age 16 wks; 2) the age-related increases in bone mass, structural cortical parameters, and in some biomechanical property parameters plateau at an older age in male than in female rats; and 3) bone growth and remodeling significantly decreased with age indistinctive of the gender.