bassianolide and Lordosis

Lordosis in fish is an abnormal ventral curvature of the vertebral column, accompanied by abnormal calcification of the afflicted vertebrae. Incidences of lordosis are a major problem in aquaculture and often correlate with increased swimming activity. To understand the biomechanical causes and consequences of lordosis, we mapped the morphological changes that occur in the vertebrae of European sea bass during their development from larva to juvenile. Our micro-CT analysis of lordotic and non-lordotic vertebrae revealed significant differences in their micro-architecture. Lordotic vertebrae have a larger bone volume, flattened dorsal zygapophyses and extra lateral ridges. They also have a larger second moment of area (both lateral and dorso-ventral) than non-lordotic vertebrae. This morphology suggests lordotic vertebrae to be adapted to an increased bending moment, caused by the axial musculature during increased swimming activity. We hypothesize the increase in swimming activity to have a two-fold effect in animals that become lordotic. The first effect is buckling failure of the axial skeleton due to an increased compressive load. The second effect is extra bone deposition as an adaptive response of the vertebrae at the cellular level, caused by an increased strain and strain rate in these vertebrae. Lordosis thus comprises both a buckling failure of the vertebral column and a molecular response that adapts the lordotic vertebrae to a new loading regime.

Topics: Adaptation, Physiological; Anatomy, Cross-Sectional; Animals; Bass; Calcinosis; Lordosis; Radiographic Image Interpretation, Computer-Assisted; Spine; Weight-Bearing

Mammalian bone is an active tissue in which osteoblasts and osteoclasts balance bone mass. This process of adaptive modelling and remodelling is probably regulated by strain-sensing osteocytes. Bone of advanced teleosts is acellular yet, despite the lack of osteocytes, it is capable of an adaptive response to physical stimuli. Strenuous exercise is known to induce lordosis. Lordosis is a ventrad curvature of the vertebral column, and the affected vertebrae show an increase in bone formation. The effects of lordosis on the strain distribution in sea bass (Dicentrarchus labrax L.) vertebrae are assessed using finite element modelling. The response of the local tissue is analyzed spatially and ontogenetically in terms of bone volume. Lordotic vertebrae show a significantly increased strain energy due to the increased load compared with normal vertebrae when loaded in compression. High strain regions are found in the vertebral centrum and parasagittal ridges. The increase in strain energy is attenuated by a change in architecture due to the increased bone formation. The increased bone formation is seen mainly at the articular surfaces of the vertebrae, although some extra bone is formed in the vertebral centrum. Regions in which the highest strains are found do not spatially correlate with regions in which the most extensive bone apposition occurs in lordotic vertebrae of sea bass. Mammalian-like strain-regulated bone modelling is probably not the guiding mechanism in adaptive bone modelling of acellular sea bass vertebrae. Chondroidal ossification is found at the articular surfaces where it mediates a rapid adaptive response, potentially attenuating high stresses on the dorsal zygapophyses.

Topics: Adaptation, Physiological; Animals; Bass; Biomechanical Phenomena; Finite Element Analysis; Fish Diseases; Lordosis; Osteogenesis; Phylogeny; Spine