Cerebrospinal fluid outflow: a review of the historical and contemporary evidence for arachnoid villi, perineural routes, and dural lymphatics.

Cerebrospinal fluid (CSF) is produced by the choroid plexuses within the ventricles of the brain and circulates through the subarachnoid space of the skull and spinal column to provide buoyancy to and maintain fluid homeostasis of the brain and spinal cord. The question of how CSF drains from the subarachnoid space has long puzzled scientists and clinicians. For many decades, it was believed that arachnoid villi or granulations, outcroppings of arachnoid tissue that project into the dural venous sinuses, served as the major outflow route. However, this concept has been increasingly challenged in recent years, as physiological and imaging evidence from several species has accumulated showing that tracers injected into the CSF can instead be found within lymphatic vessels draining from the cranium and spine. With the recent high-profile rediscovery of meningeal lymphatic vessels located in the dura mater, another debate has emerged regarding the exact anatomical pathway(s) for CSF to reach the lymphatic system, with one side favoring direct efflux to the dural lymphatic vessels within the skull and spinal column and another side advocating for pathways along exiting cranial and spinal nerves. In this review, a summary of the historical and contemporary evidence for the different outflow pathways will be presented, allowing the reader to gain further perspective on the recent advances in the field. An improved understanding of this fundamental physiological process may lead to novel therapeutic approaches for a wide range of neurological conditions, including hydrocephalus, neurodegeneration and multiple sclerosis

Pupillometry and hindsight bias:Physiological arousal predicts compensatory behavior

According to violation–compensation models of cognitive conflict, experiences that violate expected associations evoke a common, biologically based syndrome of aversive arousal, which in turn motivates compensation efforts to relieve this arousal. However, while substantial research shows that people indeed respond with increased arousal to expectancy violating events, evidence for the motivating role of arousal is rarely found. In two within-subjects studies (N = 44 and N = 50), we demonstrate evidence for the motivating role of arousal in this violation–compensation process among university students. Using pupillometry and the hindsight bias phenomenon, we show that people respond with greater arousal when presented with expectancy violating information. In turn, we show that the pupillary response is positively related to the amount of hindsight bias being displayed. These findings provide further insights into the process underlying the hindsight bias and, crucially, support key predictions following from threat–compensation models

Clearance of erythrocytes from the subarachnoid space through cribriform plate lymphatics in female mice.

BACKGROUND Atraumatic subarachnoid haemorrhage (SAH) is associated with high morbidity and mortality. Proposed mechanisms for red blood cell (RBC) clearance from the subarachnoid space (SAS) are erythrolysis, erythrophagocytosis or through efflux along cerebrospinal fluid (CSF) drainage routes. We aimed to elucidate the mechanisms of RBC clearance from the SAS to identify targetable efflux pathways. METHODS Autologous fluorescently-labelled RBCs along with PEGylated 40 kDa near-infrared tracer (P40D800) were infused via the cisterna magna (i.c.m.) in female reporter mice for lymphatics or for resident phagocytes. Drainage pathways for RBCs to extracranial lymphatics were evaluated by in vivo and in situ near-infrared imaging and by immunofluorescent staining on decalcified cranial tissue or dural whole-mounts. FINDINGS RBCs drained to the deep cervical lymph nodes 15 min post i.c.m. infusion, showing similar dynamics as P40D800 tracer. Postmortem in situ imaging and histology showed perineural accumulations of RBCs around the optic and olfactory nerves. Numerous RBCs cleared through the lymphatics of the cribriform plate, whilst histology showed no relevant fast RBC clearance through dorsal dural lymphatics or by tissue-resident macrophage-mediated phagocytosis. INTERPRETATION This study provides evidence for rapid RBC drainage through the cribriform plate lymphatic vessels, whilst neither fast RBC clearance through dorsal dural lymphatics nor through spinal CSF efflux or phagocytosis was observed. Similar dynamics of P40D800 and RBCs imply open pathways for clearance that do not impose a barrier for RBCs. This finding suggests further evaluation of the cribriform plate lymphatic function and potential pharmacological targeting in models of SAH. FUNDING Swiss National Science Foundation (310030_189226), SwissHeart (FF191155)

T Cell Migration from Inflamed Skin to Draining Lymph Nodes Requires Intralymphatic Crawling Supported by ICAM-1/LFA-1 Interactions.

T cells are the most abundant cell type found in afferent lymph, but their migration through lymphatic vessels (LVs) remains poorly understood. Performing intravital microscopy in the murine skin, we imaged T cell migration through afferent LVs in vivo. T cells entered into and actively migrated within lymphatic capillaries but were passively transported in contractile collecting vessels. Intralymphatic T cell number and motility were increased during contact-hypersensitivity-induced inflammation and dependent on ICAM-1/LFA-1 interactions. In vitro, blockade of endothelial cell-expressed ICAM-1 reduced T cell adhesion, crawling, and transmigration across lymphatic endothelium and decreased T cell advancement from capillaries into lymphatic collectors in skin explants. In vivo, T cell migration to draining lymph nodes was significantly reduced upon ICAM-1 or LFA-1 blockade. Our findings indicate that T cell migration through LVs occurs in distinct steps and reveal a key role for ICAM-1/LFA-1 interactions in this process

Size Matters: Large Objects Capture Attention in Visual Search

Can objects or events ever capture one's attention in a purely stimulus-driven manner? A recent review of the literature set out the criteria required to find stimulus-driven attentional capture independent of goal-directed influences, and concluded that no published study has satisfied that criteria. Here visual search experiments assessed whether an irrelevantly large object can capture attention. Capture of attention by this static visual feature was found. The results suggest that a large object can indeed capture attention in a stimulus-driven manner and independent of displaywide features of the task that might encourage a goal-directed bias for large items. It is concluded that these results are either consistent with the stimulus-driven criteria published previously or alternatively consistent with a flexible, goal-directed mechanism of saliency detection

Dynamics of lymphatic regeneration and flow patterns after lymph node dissection.

Knowledge about the mechanisms of regeneration of the lymphatic vasculature after surgical trauma is essential for the development of strategies for the prevention and therapy of lymphedema. However, little is known about the alterations of lymphatic flow directly after surgical trauma. We investigated lymphatic function in mice using near-infrared imaging for a period of 4 weeks after surgeries that mimic sentinel lymph node biopsy (SLNB) or axillary lymph node dissection (ALND), by removal of the popliteal lymph node (LN) alone or together with the popliteal fat pad, respectively. SLNB-like surgery did not cause changes in lymphatic drainage in the majority of cases. In contrast, lymphatic drainage impairment shown by collecting vessel rupture, dermal backflow and rerouting of lymph flow via collateral vessels were observed after ALND-like surgery. All collateral vessels drained to the inguinal LN. These results indicate that less invasive surgery prevents lymphatic decompensation. They also reveal the development and maturation of collateral lymphatic vessels after extensive surgical trauma, which reroute the flow of lymph towards a different LN. These findings might be helpful for the development of strategies to prevent and/or treat post-surgical lymphedema

Maintaining Ethical Standards during Conservation Crises

Many species at risk in Canada and globally are at or approaching a crisis, especially where little or nothing consequential is being done to prevent extirpation. Such is the case of endangered boreal caribou (Rangifer tarandus caribou) in southern Alberta, Canada. Expedient but inadequate emergency ‘fixes’ have been experimentally implemented to arrest their decline and potential extirpation, but use of these measures raises important ethical problems. In their study of the effects of killing wolves (Canis lupus) on the Little Smoky woodland caribou population, Hervieux et al. (2014a) employed lethal methods that included shooting a firearm from a helicopter and the use of strychnine baits. Both of these methods raise critical questions with regard to animal welfare. When it is necessary to kill an animal, reliable humane procedures must be used to avoid pain or distress, and produce rapid loss of consciousness until death occurs. Also relevant are formal approvals by government and institutional animal ethics committees that adhere to Canadian Council on Animal Care (CCAC) guidelines. Shooting a moving animal from a helicopter is prone to error and not conducive to shots that quickly render animals insensitive to pain or produce a consistently quick kill. Strychnine does not meet the CCAC’s criteria for an acceptable killing method, and is specifically prohibited as an injectable option for euthanizing animals. Its use under uncontrolled conditions at bait sites is likely even less suitable. In addition, the risks of non-lethal and painful injuries from this poison and associated deaths to large numbers of non-target animals clearly contravene the CCAC guidelines for wildlife research. This study did not meet the CCAC’s guidelines and did not adhere to the Canadian Journal of Zoology’s requirement that all research must be approved by an institutional animal care committee. More broadly, and regardless of the failure of formal safeguards and implicit justifications offered by authors, we should be concerned when researchers impose suffering on wild animals and advocate for such programs to continue. Based on an apparent lack of compliance with CCAC’s guidelines, we believe that this controversial study should never have taken place and should not have been published by the Canadian Journal of Zoology. Experiments that involve the intentional inhumane killing of animals violate the fundamental principles of ethical science and rightfully endanger the reputation of science and scientists, as well as the journals willing to publish them. We recommend that CCAC guidelines be further developed to clearly address field methods used in wildlife studies, namely the shooting of animals from a helicopter, and the use of strychnine in baits. Also, independent audits should be conducted to investigate individual researchers and their studies, and the journals that publish this work, to ensure that CCAC guidelines are properly followed, even by researchers who collaborate well after the animal-based procedures have been carried out

Advanced miniature mixed mode bending setup for in-situ interface delamination characterization

A novel test frame configuration was developed and employed to design a new miniature mixed mode bending (MMMB) setup for in-situ characterization of interface delamination in miniature multi-layer structures to accomplish full range of mode mixities. This advanced setup is specially designed with sufficiently small dimensions to fit in a scanning electron microscope and under an optical microscope for detailed real-time fracture analysis during delamination. Analysis of the loads in the new test configuration was performed and a special loading configuration was identified which replicates pure mode II loading better than the conventional end notch flexure (ENF) test. Special care was taken to minimize non-linearities, such as friction, the influence of gravity and geometrical non-linearities. Finite element simulation of the designed setup were performed to show its ability to access all loading modes. Preliminary delamination tests conducted on homogeneous bilayer samples under scanning electron microscope (SEM) proved the new setup configuration is capable of measuring the crack length, crack opening profile and crack delamination mechanism in addition to the conventional energy release rate measurements

Decline of lymphatic vessel density and function in murine skin during aging.

Lymphatic vessels play important roles in the pathogenesis of many conditions that have an increased prevalence in the elderly population. However, the effects of the aging process on the lymphatic system are still relatively unknown. We have applied non-invasive imaging and whole-mount staining techniques to assess the lymphatic vessel function and morphology in three different age groups of mice: 2 months (young), 7 months (middle-aged), and 18 months (aged). We first developed and validated a new method to quantify lymphatic clearance from mouse ear skin, using a lymphatic-specific near-infrared tracer. Using this method, we found that there is a prominent decrease in lymphatic vessel function during aging since the lymphatic clearance was significantly delayed in aged mice. This loss of function correlated with a decreased lymphatic vessel density and a reduced lymphatic network complexity in the skin of aged mice as compared to younger controls. The blood vascular leakage in the skin was slightly increased in the aged mice, indicating that the decreased lymphatic function was not caused by a reduced capillary filtration in aged skin. The decreased function of lymphatic vessels with aging might have implications for the pathogenesis of a number of aging-related diseases

Beyond Trial and Error: A Systematic Development of Liposomes Targeting Primary Macrophages

Monocytes/macrophages are phagocytic innate immune cells playing a pivotal role in tissue homeostasis, inflammation, and antitumor immunity in a microenvironment-dependent manner. By expressing pattern recognition and scavenger receptors on their surface, macrophages selectively take up pathogens, cellular debris, and often—undesirably—drug delivery systems. On the other hand, the propensity of phagocytic cells to internalize particulate drug carriers is used to load them with a cargo of choice, turning the monocytes/macrophages into a diagnostic or therapeutic Trojan horse. Identifying the ideal physicochemical properties of particulate carriers such as liposomes to achieve the most efficient macrophage-mediated drug delivery has been object of extensive research in the past, but the studies reported so far rely solely on trial-and-error approaches. Herein, a design of experiment (DoE) strategy to identify the optimal liposomal formulation is proposed, fully characterized in terms of size, surface charge, and membrane fluidity, to maximize macrophage targeting. The findings are validated using mouse bone marrow-derived macrophages, a primary preparation modeling in vivo monocyte-derived macrophages, thus confirming the robustness and versatility of the systematic and iterative approach and suggesting the promising potential of the DoE approach for the design of cell-targeting delivery systems