Interaction of hyperbaric nitrogen and oxygen effects on behavior.

Breathing elevated environmental pressures of nitrogen and oxygen produced changes in behavior of rats that evidenced an interaction between the two gases. Rates of responding generated by a fixed-interval schedule of reinforcement systematically changed as partial pressures of nitrogen were elevated from 0.8 to 10.4 ATA. Response rates increased above baseline followed by a decline in rates as a function of increasing nitrogen pressure. Concurrent increases in partial pressures of oxygen from 0.2 to 2.2 ATA potentiated the rate-increasing effects of nitrogen at low to moderate nitrogen pressures and enhanced rate-decreasing effects at higher nitrogen pressures. Raised oxygen pressures modulated and interacted with the narcotic effects of nitrogen on behavior.