Figure 1.

Diagram of the present experiments. Retinal segments or eye cups prepared from Sprague-Dawley rats were placed in plastic dishes that were 5 mm high and 2.5 cm in diameter. Each dish was suspended by a long stainless steel wire hooked through a hole in the lateral wall. With the wire, the specimen in the dish was slowly submerged to the bottom of a tall glass cylinder filled with aCSF at 30°C and left for 24 hours. The wire was fixed at the top of the cylinder after the dish was settled at the bottom of the cylinder. The diameter of the glass cylinder was 3 cm, and the height was 20, 50, 80, or 120 cm. Hydrostatic pressure at the bottom of the cylinder was calculated to be 10, 25, 50, or 75 mm Hg when aCSF was added to a height of 13.5, 33.7, 67.3, or 101.2 cm, respectively. The medium was constantly bubbled with 95% O₂–5% CO₂ throughout the experiments. The minimum gas pressure needed to drive gas through the PE90 plastic tubing was monitored before incubation. This minimum gas pressure reflects the pressure at the bottom of the open, tall cylinder. Glutamate, GYKI, or MK-801 was added to the aCSF during some experiments.