Multi-cellular rosettes in the mouse visceral endoderm facilitate the ordered migration of anterior visceral endoderm cells.

The visceral endoderm (VE) is a simple epithelium that forms the outer layer of the egg-cylinder stage mouse embryo. The anterior visceral endoderm (AVE), a specialised subset of VE cells, is responsible for specifying anterior pattern. AVE cells show a stereotypic migratory behaviour within the VE, which is responsible for correctly orientating the anterior-posterior axis. The epithelial integrity of the VE is maintained during the course of AVE migration, which takes place by intercalation of AVE and other VE cells. Though a continuous epithelial sheet, the VE is characterised by two regions of dramatically different behaviour, one showing robust cell movement and intercalation (in which the AVE migrates) and one that is static, with relatively little cell movement and mixing. Little is known about the cellular rearrangements that accommodate and influence the sustained directional movement of subsets of cells (such as the AVE) within epithelia like the VE. This study uses an interdisciplinary approach to further our understanding of cell movement in epithelia. Using both wild-type embryos as well as mutants in which AVE migration is abnormal or arrested, we show that AVE migration is specifically linked to changes in cell packing in the VE and an increase in multi-cellular rosette arrangements (five or more cells meeting at a point). To probe the role of rosettes during AVE migration, we develop a mathematical model of cell movement in the VE. To do this, we use a vertex-based model, implemented on an ellipsoidal surface to represent a realistic geometry for the mouse egg-cylinder. The potential for rosette formation is included, along with various junctional rearrangements. Simulations suggest that while rosettes are not essential for AVE migration, they are crucial for the orderliness of this migration observed in embryos. Our simulations are similar to results from transgenic embryos in which Planar Cell Polarity (PCP) signalling is disrupted. Such embryos have significantly reduced rosette numbers, altered epithelial packing, and show abnormalities in AVE migration. Our results show that the formation of multi-cellular rosettes in the mouse VE is dependent on normal PCP signalling. Taken together, our model and experimental observations suggest that rosettes in the VE epithelium do not form passively in response to AVE migration. Instead, they are a PCP-dependent arrangement of cells that acts to buffer the disequilibrium in cell packing generated in the VE by AVE migration, enabling AVE cells to migrate in an orderly manner.

Oxygen reduces tourniquet-associated pain: a double-blind, randomized, controlled trial for application in hand surgery.

BACKGROUND: Why do limb tourniquets cause pain? If ischemia is the mechanism, can supplemental oxygen reduce pain? The Reducing Tourniquet Associated Pain study investigated whether this simple treatment could extend tourniquet tolerance time to facilitate hand surgery under local or regional anesthesia. METHODS: The Reducing Tourniquet Associated Pain study was a double-blind, randomized, controlled trial of healthy volunteers. Participants received either 50% inhaled oxygen or air placebo via a face mask for 3 minutes before and up to 30 minutes after upper arm tourniquet inflation to 250 mmHg. Pain scores were recorded at 2-minute intervals using a validated 100-mm visual analogue scale. The primary outcomes were (1) difference in visual analogue scale score and (2) difference in time taken to reach visual analogue score of 40 mm or more in oxygen and air groups. RESULTS: Fifty participants enrolled and, after exclusion criteria were applied, 46 were analyzed (oxygen, n = 23; air, n = 23). Oxygen supplementation was associated with a 29 percent mean reduction in pain on visual analogue scoring compared with air placebo over the entire period of inhalation (p = 0.027). Oxygen also extended the time to visual analogue scale score of 40 mm or more by a mean of 6½ minutes compared with air placebo (p = 0.008). CONCLUSIONS: Oxygen is a readily available, low-risk, low-cost treatment that significantly reduced tourniquet-associated pain in this study and significantly increased the time taken to reach visual analogue scale score of 40 or more. The authors recommend oxygen to facilitate hand surgery under a tourniquet and when a regional block fails to control tourniquet pain.

Spontaneous surgical emphysema of the larynx following hyperextension of the neck.

Surgical emphysema of the larynx is rare in the absence of trauma and there are a paucity of case reports that describe such conditions. We present what we believe to be an unusual, atraumatic mechanism for mucosal breech of the larynx with subsequent surgical emphysema. Nasendoscopy revealed oedema of the arytenoid cartilage and computed tomography revealed moderate subcutaneous emphysema of the larynx. No fracture was seen. After conservative management the patient made a complete recovery.