Biochemical and biomechanical characterisation of equine cervical facet joint cartilage.

BACKGROUND: The equine cervical facet joint is a site of significant pathology. Located bilaterally on the dorsal spine, these diarthrodial joints work in conjunction with the intervertebral disc to facilitate appropriate spinal motion. Despite the high prevalence of pathology in this joint, the facet joint is understudied and thus lacking in viable treatment options. OBJECTIVE: The goal of this study was to characterise equine facet joint cartilage and provide a comprehensive database describing the morphological, histological, biochemical and biomechanical properties of this tissue. STUDY DESIGN: Descriptive cadaver studies. METHODS: A total of 132 facet joint surfaces were harvested from the cervical spines of six skeletally mature horses (11 surfaces per animal) for compiling biomechanical and biochemical properties of hyaline cartilage of the equine cervical facet joints. Gross morphometric measurements and histological staining were performed on facet joint cartilage. Creep indentation and uniaxial strain-to-failure testing were used to determine the biomechanical compressive and tensile properties. Biochemical assays included quantification of total collagen, sulfated glycosaminoglycan and DNA content. RESULTS: The facet joint surfaces were ovoid in shape with a flat articular surface. Histological analyses highlighted structures akin to articular cartilage of other synovial joints. In general, biomechanical and biochemical properties did not differ significantly between the inferior and superior joint surfaces as well as among spinal levels. Interestingly, compressive and tensile properties of cervical facet articular cartilage were lower than those of articular cartilage from other previously characterised equine joints. Removal of the superficial zone reduced the tissue's tensile strength, suggesting that this zone is important for the tensile integrity of the tissue. MAIN LIMITATIONS: Facet surfaces were sampled at a single, central location and do not capture the potential topographic variation in cartilage properties. CONCLUSIONS: This is the first study to report the properties of equine cervical facet joint cartilage and may serve as the foundation for the development of future tissue-engineered replacements as well as other treatment strategies.

Biophysical properties of the surface of desiccation-tolerant mutants and parental strain of the entomopathogenic nematode Heterorhabditis megidis (strain UK211).

Entomopathogenic nematodes (EPN) are useful biological control agents of insect pests. However, the infective juvenile (IJ) stage which is the only stage to occur outside the host is susceptible to environmental extremes such as desiccation. We have isolated desiccation-tolerant strains of the EPN Heterorhabditis megidis. In this paper we describe the surface properties of these desiccation-tolerant mutants. Heterorhabditid IJs retain the sheath of the previous larval stage. The mutant lines possess alterations in the surface properties of the sheath. Differences were observed in fluorescent lipid analogue insertion into the surface of the sheath. Furthermore, cationized ferritin-binding studies demonstrated that the mutant lines possessed an increase in net negative surface charge. Removal of the surface layer of the sheath resulted in the loss of the mutant phenotype and in a reduction in the desiccation tolerance of the parental strain. Therefore, the negatively charged 'surface coat' appears to play an important role in the desiccation tolerance of Heterorhabditis species.

The effect of day of emergence from the insect cadaver on the behavior and environmental tolerances of infective juveniles of the entomopathogenic nematode Heterorhabditis megidis (strain UK211).

Infective juveniles (IJs) of entomopathogenic nematodes (EPNs) are obligate parasites of insect larvae. Inside the host they develop into sexually mature adult stages and complete their life cycle. Two or 3 adult nematode generations can occur in the insect host. The increase in nematode population density in the insect cadaver, together with limiting nutrient conditions, result in the formation of IJs. These IJs emerge into the soil to search for a new host. It typically takes 7-8 days for all IJs to emerge from a parasitized insect. We have investigated the effect of the day of emergence of IJs from insect cadavers on the environmental tolerance and behavior of the EPN Heterorhabditis megidis strain UK211. The IJs that emerge early display good initial host-finding ability and increased temperature tolerance but disperse poorly and have poor tolerance to desiccation. Conversely, the IJs that emerge later display poor initial host-finding ability and poor temperature tolerance but they disperse well and possess increased desiccation tolerance. These phenotypic differences are likely to facilitate early-emerging IJs in locating and infecting hosts in the vicinity of the cadaver, whereas IJs that emerge late are adapted to disperse away from their natal cadaver. We hypothesize that adaptive phenotypic plasticity rather than allelic variability may provide the genetic basis for the different physiological and behavioral phenotypes of the early- and late-emerging IJs.