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1. Hypoxia‐enhanced adhesion of red blood cells in microscale flow

   https://doi.org/10.1111/micc.12374  

   Kim, Myeongseop; Alapan, Yunus; Adhikari, Anima; Little, Jane A.; Gurkan, Umut A. (July 2017, Microcirculation)

   Abstract ObjectivesThe advancement of microfluidic technology has facilitated the simulation of physiological conditions of the microcirculation, such as oxygen tension, fluid flow, and shear stress in these devices. Here, we present a micro‐gas exchanger integrated with microfluidics to studyRBCadhesion under hypoxic flow conditions mimicking postcapillary venules. MethodsWe simulated a range of physiological conditions and exploredRBCadhesion to endothelial or subendothelial components (FNorLN). Blood samples were injected into microchannels at normoxic or hypoxic physiological flow conditions. Quantitative evaluation ofRBCadhesion was performed on 35 subjects with homozygousSCD. ResultsSignificant heterogeneity inRBCadherence response to hypoxia was seen amongSCDpatients.RBCs from a HEA population showed a significantly greater increase in adhesion compared toRBCs from a HNA population, for bothFNandLN. ConclusionsThe approach presented here enabled the control of oxygen tension in blood during microscale flow and the quantification ofRBCadhesion in a cost‐efficient and patient‐specific manner. We identified a unique patient population in whichRBCs showed enhanced adhesion in hypoxia in vitro. Clinical correlates suggest a more severe clinical phenotype in this subgroup. 

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2. Capuchin and rhesus monkeys show sunk cost effects in a psychomotor task

   https://doi.org/10.1038/s41598-020-77301-w  

   Watzek, Julia; Brosnan, Sarah F. (November 2020, Scientific Reports)

   Abstract Human decision-making is often swayed by irrecoverable investments even though it should only be based on future—and not past—costs and benefits. Although this sunk cost effect is widely documented and can lead to devastating losses, the underlying psychological mechanisms are unclear. To tease apart possible explanations through a comparative approach, we assessed capuchin and rhesus monkeys’ susceptibility to sunk costs in a psychomotor task. Monkeys needed to track a moving target with a joystick-controlled cursor for variable durations. They could stop at any time, ending the trial without reward. To minimize the work required for a reward, monkeys should have always persisted for at least 1 s, but should have abandoned the trial if that did not yield a reward. Capuchin monkeys and especially rhesus macaques persisted to trial completion even when it was suboptimal, and were more likely to complete the trial the longer they had already tracked the target. These effects were less pronounced, although still present, when the change in expected tracking duration was signalled visually. These results show that sunk cost effects can arise in the absence of human-unique factors and may emerge, in part, because persisting can resolve uncertainty. 

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3. The Joint Simon task is not joint for capuchin monkeys

   https://doi.org/10.1038/s41598-024-55885-x  

   Martínez, Mayte; Babb, Matthew H.; Range, Friederike; Brosnan, Sarah F. (March 2024, Scientific Reports)

   Abstract Human cooperation can be facilitated by the ability to create a mental representation of one’s own actions, as well as the actions of a partner, known as action co-representation. Even though other species also cooperate extensively, it is still unclear whether they have similar capacities. The Joint Simon task is a two-player task developed to investigate this action co-representation. We tested brown capuchin monkeys (Sapajus [Cebus] apella), a highly cooperative species, on a computerized Joint Simon task and found that, in line with previous research, the capuchins' performance was compatible with co-representation. However, a deeper exploration of the monkeys’ responses showed that they, and potentially monkeys in previous studies, did not understand the control conditions, which precludes the interpretation of the results as a social phenomenon. Indeed, further testing to investigate alternative explanations demonstrated that our results were due to low-level cues, rather than action co-representation. This suggests that the Joint Simon task, at least in its current form, cannot determine whether non-human species co-represent their partner’s role in joint tasks. 

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4. Hemodynamic Characteristics of a Tortuous Microvessel Using High‐Fidelity Red Blood Cell Resolved Simulations

   https://doi.org/10.1111/micc.12875  

   Hossain, Mir Md Nasim; Hu, Nien‐Wen; Kazempour, Ali; Murfee, Walter L.; Balogh, Peter (July 2024, Microcirculation)

   ABSTRACT ObjectiveTortuous microvessels are characteristic of microvascular remodeling associated with numerous physiological and pathological scenarios. Three‐dimensional (3D) hemodynamics in tortuous microvessels influenced by red blood cells (RBCs), however, are largely unknown, and important questions remain. Is blood viscosity influenced by vessel tortuosity? How do RBC dynamics affect wall shear stress (WSS) patterns and the near‐wall cell‐free layer (CFL) over a range of conditions? The objective of this work was to parameterize hemodynamic characteristics unique to a tortuous microvessel. MethodsRBC‐resolved simulations were performed using an immersed boundary method‐based 3D fluid dynamics solver. A representative tortuous microvessel was selected from a stimulated angiogenic network obtained from imaging of the rat mesentery and digitally reconstructed for the simulations. The representative microvessel was a venule with a diameter of approximately 20 μm. The model assumes a constant diameter along the vessel length and does not consider variations due to endothelial cell shapes or the endothelial surface layer. ResultsMicrovessel tortuosity was observed to increase blood apparent viscosity compared to a straight tube by up to 26%. WSS spatial variations in high curvature regions reached 23.6 dyne/cm²over the vessel cross‐section. The magnitudes of WSS and CFL thickness variations due to tortuosity were strongly influenced by shear rate and negligibly influenced by tube hematocrit levels. ConclusionsNew findings from this work reveal unique tortuosity‐dependent hemodynamic characteristics over a range of conditions. The results provide new thought‐provoking information to better understand the contribution of tortuous vessels in physiological and pathological processes and help improve reduced‐order models. 

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5. Social and demographic correlates of male androgen levels in wild white‐faced capuchin monkeys ( Cebus capucinus )

   https://doi.org/10.1002/ajp.22653  

   Schaebs, Franka S.; Perry, Susan E.; Cohen, Don; Mundry, Roger; Deschner, Tobias (April 2017, American Journal of Primatology)

   The Challenge Hypothesis, designed originally to explain the patterning of competitive behavior and androgen levels in seasonally breeding birds, predicts that males will increase their androgen levels in order to become more competitive in reproductive contexts. Here we test predictions derived from the Challenge Hypothesis in white‐faced capuchin monkeys (Cebus capucinus), a species that has somewhat seasonal reproduction. We analyzed demographic and hormonal data collected over a 5.25‐year period, from 18 males in nine social groups living in or near Lomas Barbudal Biological Reserve, Costa Rica. Alpha males had higher androgen levels than subordinates. Contrary to our predictions, neither the number of breeding‐age males nor the number of potentially fertile females was obviously associated with androgen levels. Furthermore, male androgen levels were not significantly linked to social stability, as measured by stability of male group membership or recency of change in the alpha male position. Androgen levels changed seasonally, but not in a manner that had an obvious relationship to predictions from the Challenge Hypothesis: levels were generally at their lowest near the beginning of the conception season, but instead of peaking when reproductive opportunities were greatest, they were at their highest near the end of the conception season or shortly thereafter. This lack of correspondence to the timing of conceptions suggests that there may be ecological factors not yet identified that influence ifA levels. We expected that the presence of offspring who were young enough to be vulnerable to infanticide during an alpha male takeover might influence androgen levels, at least in the alpha male, but this variable did not significantly impact results. 

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