The retina and retinal pigment epithelium differ in nitrogen metabolism and are metabolically connected.

Defects in energy metabolism in either the retina or the immediately adjacent retinal pigment epithelium (RPE) underlie retinal degeneration, but the metabolic dependence between retina and RPE remains unclear. Nitrogen-containing metabolites such as amino acids are essential for energy metabolism. Here, we found that 15N-labeled ammonium is predominantly assimilated into glutamine in both the retina and RPE/choroid ex vivo [15N]Ammonium tracing in vivo show that, like the brain, the retina can synthesize asparagine from ammonium, but RPE/choroid and the liver cannot. However, unless present at toxic concentrations, ammonium cannot be recycled into glutamate in the retina and RPE/choroid. Tracing with 15N-labeled amino acids show that the retina predominantly uses aspartate transaminase for de novo synthesis of glutamate, glutamine, and aspartate, whereas RPE uses multiple transaminases to utilize and synthesize amino acids. Retina consumes more leucine than RPE, but little leucine is catabolized. The synthesis of serine and glycine is active in RPE but limited in the retina. RPE, but not the retina, uses alanine as mitochondrial substrates through mitochondrial pyruvate carrier. However, when the mitochondrial pyruvate carrier is inhibited, alanine may directly enter the retinal mitochondria but not those of RPE. In conclusion, our results demonstrate that the retina and RPE differ in nitrogen metabolism and highlight that the RPE supports retinal metabolism through active amino acid metabolism.

Duplication of the inferior vena cava: evidence of a novel type IV.

Anatomical variations of the inferior vena cava, including the double inferior vena cava or isolated left inferior vena cava, are uncommon and of great clinical importance. Inferior vena cava variations signify predisposition to deep vein thrombosis and may complicate retroperitoneal surgeries including abdominal aortic surgery. Failure to recognize such variations may predispose a patient to life- threatening complications. This prospective anatomical study assessed 129 cadavers for variations of the inferior vena cava. One of the 129 cadavers (0.78%) possessed a double inferior vena cava and none (0%) possessed an isolated left inferior vena cava. The left-sided inferior vena cava was of a larger diameter than that of the right-sided inferior vena cava - opposite of what would be seen in a Type III duplication. Therefore, this observation expands the three-type classification system to include a Type IV duplication.

Locating the foramen ovale by using molar and inter-eminence planes: a guide for percutaneous trigeminal neuralgia procedures.

OBJECTIVE: The first attempt to cannulate the foramen ovale is oftentimes unsuccessful and requires subsequent reattempts, thereby increasing the risk of an adverse event and radiation exposure to the patient and surgeon. Failure in cannulation may be attributable to variation in soft-tissue-based landmarks used for needle guidance. Also, the incongruity between guiding marks on the face and bony landmarks visible on fluoroscopic images may also complicate cannulation. Therefore, the object of this study was to assess the location of the foramen ovale by way of bony landmarks, exclusive of soft-tissue guidance. METHODS: A total of 817 foramina ovalia (411 left-sided, 406 right-sided) from cranial base images of 424 dry crania were included in the study. The centroid point of each foramen ovale was identified. A sagittal plane through the posterior-most molar (molar plane) and a coronal plane passing through the articular eminences of the temporal bones (inter-eminence plane) were superimposed on images. The distances of the planes from the centroids of the foramina were measured. Also, counts were taken to assess how often the planes and their intersections crossed the boundary of the foramen ovale. RESULTS: The average distance between the molar plane and the centroid of the foramen was 1.53 ± 1.24 mm (mean ± SD). The average distance between the inter-eminence plane and the centroid was 1.69 ± 1.49 mm. The molar and inter-eminence planes crossed through the foramen ovale boundary 83.7% (684/817) and 81.6% (667/817) of the time, respectively. The molar and inter-eminence planes passed through the boundary of the foramen together 73.5% (302/411) of the time. The molar and inter-eminence planes intersected within the boundary of the foramen half of the time (49.4%; 404/817). CONCLUSIONS: The results of this study provide a novel means of identifying the location of the foramen ovale. Unlike the soft-tissue landmarks used in the many variations of the route of Härtel, the bony landmarks identified in this study can be palpated, marked on the face, appreciated fluoroscopically, and do not require any measurement from soft-tissue structures. Utilizing the molar and inter-eminence planes as cannulation guides will improve the approach to the foramen ovale and decrease the amount of radiation exposure to both the patient and surgeon.