Age-Related Adaptation of Bone-PDL-Tooth Complex: Rattus-Norvegicus as a Model System

Functional loads on an organ induce tissue adaptations by converting mechanical energy into chemical energy at a cell-level. The transducing capacity of cells alters physico-chemical properties of tissues, developing a positive feedback commonly recognized as the form-function relationship. In this study, organ and tissue adaptations were mapped in the bone-tooth complex by identifying and correlating biomolecular expressions to physico-chemical properties in rats from 1.5 to 15 months. However, future research using hard and soft chow over relevant age groups would decouple the function related effects from aging affects. Progressive curvature in the distal root with increased root resorption was observed using micro X-ray computed tomography. Resorption was correlated to the increased activity of multinucleated osteoclasts on the distal side of the molars until 6 months using tartrate resistant acid phosphatase (TRAP). Interestingly, mononucleated TRAP positive cells within PDL vasculature were observed in older rats. Higher levels of glycosaminoglycans were identified at PDL-bone and PDL-cementum entheses using alcian blue stain. Decreasing biochemical gradients from coronal to apical zones, specifically biomolecules that can induce osteogenic (biglycan) and fibrogenic (fibromodulin, decorin) phenotypes, and PDL-specific negative regulator of mineralization (asporin) were observed using immunohistochemistry. Heterogeneous distribution of Ca and P in alveolar bone, and relatively lower contents at the entheses, were observed using energy dispersive X-ray analysis. No correlation between age and microhardness of alveolar bone (0.7±0.1 to 0.9±0.2 GPa) and cementum (0.6±0.1 to 0.8±0.3 GPa) was observed using a microindenter. However, hardness of cementum and alveolar bone at any given age were significantly different (P<0.05). These observations should be taken into account as baseline parameters, during development (1.5 to 4 months), growth (4 to 10 months), followed by a senescent phase (10 to 15 months), from which deviations due to experimentally induced perturbations can be effectively investigated

The evolutionary psychology of leadership trait perception

Knowles, Kristen K. - ORCID 0000-0001-9664-9055 https://orcid.org/0000-0001-9664-9055Many researchers now approach the understanding of how facial characteristics shape the perception of leadership ability through the lens of human evolution. This approach considers what skills and characteristics would have been valuable for leaders to possess in our evolutionary history, including dominance, masculinity, and trustworthiness. Moreover, it gives an understanding about why rapid categorisation of these social cues from faces is adaptive. In this chapter, I present evolutionary arguments for social inferences based on faces, and discuss how our understanding of this categorisation has shifted away from purely associative phenomena towards evolved, innate processes. I explain how the perception of leadership ability in faces is linked to variance in facial morphology, and how these morphologies tell us something about the individuals who carry them. Specific facial cues relating to leadership-relevant traits are discussed, as well as the underlying biological systems that accompany these traits. I also explain the importance of context and individual differences on the prioritisation of seemingly disparate facial cues to leadership: dominance and trustworthiness. I also discuss recent findings in this area which further extend these concepts to examine cues to leadership in women’s faces, generally overlooked by evolutionary psychologists, and how political ideology can interact with these effects.https://doi.org/10.1007/978-3-319-94535-4_5pubpu