Thickness of the Stifle Joint Articular Cartilage in Different Large Animal Models of Cartilage Repair and Regeneration.

OBJECTIVE: Regulatory guidelines for preclinical cartilage repair studies suggest large animal models (e.g., sheep, goat, [mini]-pig, or horse) to obtain results representative for humans. However, information about the 3-dimensional thickness of articular cartilage at different implantation sites in these models is limited. DESIGN: To identify the most suitable site for experimental surgery, cartilage thickness at the medial femoral condyle (MFC), lateral femoral condyle (LFC), and trochlea in ovine, caprine, and porcine cadaver stifle joints was systematically measured using hematoxylin-eosin staining of 6 µm paraffin sections and software-based image analysis. RESULTS: Regarding all ventral-dorsal regions of the MFC, goat showed the thickest articular cartilage (maximal mean thickness: 1299 µm), followed by sheep (1096 µm) and mini-pig (604 µm), with the highest values in the most ventral and dorsal regions. Also for the LFC, the most ventral regions showed the thickest cartilage in goat (maximal mean thickness: 1118 µm), followed by sheep (678 µm) and mini-pig (607 µm). Except for the mini-pig, however, the cartilage thickness on the LFC was consistently lower than that on the MFC. The 3 species also differed along the transversal measuring points on the MFC and LFC. In contrast, there were no consistent differences for the regional cartilage thickness of the trochlea among goat and sheep (≥780 µm) and mini-pig (≤500 µm). CONCLUSIONS: Based on their cartilage thickness, experimental defects on goat and sheep MFC may be viable options for preclinical cartilage repair studies, in addition to well-established horse models.

Integration of opposing semaphorin guidance cues in cortical axons.

Previous work demonstrated that members of the semaphorin family, Sema3A and Sema3C, act as repulsive and attractive guidance signals, respectively, for cortical axons. During the development of corticofugal projections, these semaphorins are expressed in adjacent cortical zones, but there is a considerable overlap between Sema3A and Sema3C expression in the subventricular zone. We used different in vitro assays to examine the response of cortical axons exposed to defined mixtures of these opposing guidance cues. Results showed that even at very low concentrations, Sema3A overrides the effects of Sema3C. Moreover, experiments with function-blocking antibodies directed against neuropilin provided insights into how cortical axons integrate disparate guidance signals at the receptor level. These in vitro data suggest that the pathway of corticofugal axons is defined by an attractive cue in the intermediate zone, where Sema3C is expressed alone. To directly test this hypothesis in vivo, we performed axon-tracing experiments in Sema3C-deficient mice. Compared with wild-type animals, corticofugal axons take a more superficial route in Sema3C(-/-) mice, and the corticofugal pathway is more compacted. This phenotype is expected when an attractive cue for cortical axons, Sema3C, is eliminated and a repulsive cue, Sema3A, becomes predominant.

Cytocompatibility of polymer-based periodontal bone substitutes in gingival fibroblast and MC3T3 osteoblast cell cultures.

OBJECTIVES: Inflammatory periodontal diseases are accompanied by destruction of periodontal tissue and alveolar bone. Infrabony lesions can be regenerated with adequate bone substitutes, which require high biocompatibility of the material. METHODS: To rate the biocompatibility of nine polymeric periodontal bone substitutes (Bio 1-Bio 9), cell viability and cytotoxicity assays were performed. For viability, human gingival fibroblasts (HGFs) and MC3T3 osteoblasts were cultured on the bone substitutes. For cytotoxicity, biomaterial extracts were prepared by incubation with culture medium for maximally 28days, and cells were exposed to the extracts for 1day. Polymers Bio 1 to Bio 5 were prepared by solvent casting, Bio 6 to Bio 9 by photopolymerization of the monomers at wavelengths of 400-500nm in the presence of a suitable photoinitiation system. RESULTS: Bio 1, Bio 3, Bio 4, Bio 5, and Bio 7 showed moderate to excellent cytocompatibility for both HGFs and osteoblasts in viability tests. Together with the results of the cytotoxicity assays, four of the nine tested polymers were considered cytocompatible: Bio 1 (poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate; PVB)), Bio 4 and Bio 5 (functionalized oligolactones), and, to a limited degree, Bio 7 (urethane methacrylate). Except for Bio 7, the cytocompatible polymers showed intermediate water contact angles (74-85°) and therefore moderate to low hydrophilicity. SIGNIFICANCE: The non-cross-linked polymers Bio 1, Bio 4, or Bio 5, and the photopolymerized polymeric network Bio 7 display good/excellent cytocompatibility and are therefore potential candidates for tissue engineering in alveolar bone substitution.

Neurotransmitters and the development of neuronal circuits.

In the mature brain, neurotransmitters are used for synaptic communication between neurons. But during nervous system development, neurons often express and release transmitters before their axons establish contacts with their target cells. While much is known about the synaptic effects of neurotransmitters, their extrasynaptic effects are less understood. There is increasing evidence that neurotransmitters in the immature nervous system can act as trophic factors that influence different developmental events such as cell proliferation and differentiation. However, more recent work demonstrates that neurotransmitters can also influence the targeting of migrating neurons and growing axons during the formation of neuronal circuits. This chapter will focus on such guidance effects of neurotransmitters during the development of the nervous system. Elucidating extrasynaptic functions during the nervous system development might also provide insights in their potential roles for plasticity and regeneration in the adult nervous system.