Effects of ischemia-like conditions on cultured neurons: Protection by low Na⁺, low Ca²⁺ solutions

An in vitro system was used to mimic several aspects of ischemia, including low oxygen pressure, low nutrient levels, and the accumulation of cellular products thought to contribute to damage during ischemia. We replaced normal culture medium from 3-week-old basal ganglia cultures with oxygen-depleted, nutrient-deficient medium. After incubation in an atmosphere of 94% N₂, 6% CO₂ for 5 hr at 37°C, the cultures were returned to normal medium. After a 24 hr recovery period, cell viability was assessed in terms of cell number, electrophysiological properties, and immunohistochemical markers. When the medium used during the ischemic period was a normal balanced salt solution, more than 70% of the cells were damaged by the low-oxygen, low-glucose stress. Loss of cell processes and cell swelling were the most evident signs of damage. The majority of the cells remaining viable were astrocytes. Neuronal damage was observed only when both glucose and oxygen were deficient. Some damage was evident even at oxygen tensions of 60 mm Hg when glucose was absent from the medium; much more extensive damage was observed at tensions below 1.0 mm Hg. Lowering both extracellular sodium and calcium resulted in more than a 2-fold increase in survival (70 vs 28%). These results indicate that damage to neurons during conditions of extreme energy deprivation such as ischemia may be mediated by the influx of calcium and/or sodium.