Effects of nitrogen and helium at pressure on drug-induced stereotypy and locomotion in mice.

Stereotyped behavior was induced in mice by apomorphine (5-50 mg X kg-1 s.c.) and d-amphetamine (3-5 mg X kg-1 i.p.), and increased locomotor activity was induced by d-amphetamine (8 and 10 mg X kg-1 i.p.) and by morphine sulfate (15 and 30 mg X kg-1 i.p.). Experiments were conducted at 1, 4, and 7 ATA. All mice were myringotomized under ether anesthesia 3 d before behavioral studies to minimize disturbances due to pressure differences across the tympanic membrane during compression. Compressed air significantly increased locomotor activity induced by d-amphetamine and morphine sulfate whereas He/O2 had no effect, suggesting that the change was due to the narcotic effect of N2. Drug-induced stereotyped behavior was affected variably (usually depressed) by compressed air and not by He/O2. Since both stereotypy and locomotor activity induced by these drugs involve dopamine receptor systems, the results suggest that compressed air does not influence all such membrane receptors in like manner. Evidence for receptor plasticity is discussed.