Folic acid (80 μg/kg intraperitoneally) markedly increases the percentage of regenerated (i.e., Fluorogold-positive) dorsal root ganglia (DRG) neurons (protocol 2b) compared with no folic acid (FA) control (protocol 2a), single 80% N₂O exposure (protocol 2c), serial 40% N₂O exposure (protocol 2e), and serial 80% N₂O exposure (protocol 2g). A single exposure to 80% N₂O (protocol 2d), serial exposure to 40% N₂O (protocol 2f), and serial exposure to 80% N₂O (protocol 2h) reverses the benefit of serial folic acid administration. Table 3 provides the number of animals used to compare the percentage of regenerating dorsal root ganglia neurons after sharp spinal cord injury.