Anxiolytic effects of nitrous oxide in mice in the light-dark and holeboard exploratory tests.
To investigate anxiolytic effects of nitrous oxide (N2O), male mice were tested in two exploratory models--a two-chambered light-dark (L-D) unit and a holeboard. Tests were conducted inside a glovebag through which one of three mixtures of N2O and oxygen (25, 50 and 75% N2O) or room air (RA) was circulated at a flow rate of 10 l/min. The principal findings in the L-D unit were a concentration-related increase in number of interdepartmental transitions and a generalized increase in time spent on the light side. Nitrous oxide effectively elevated transitions in the L-D unit at a lower concentration (25% N2O) than was required to increase locomotor activity in an open field (50% N2O), suggesting that these two measures are at least partially independent; transitions might reflect a specific exploratory component of locomotor behavior. In the holeboard test, a concentration-related increase in number of head dips was observed. Pretreatment with naltrexone-HCl or saline vehicle revealed a contribution by an endogenous opioid-linked locomotor stimulant effect in some measures. A dose-related reversal by flumazenil of 50% N2O-induced shifts in number of head dips and time spent head-dipping implicates a benzodiazepine receptor. Both paradigms, in particular the holeboard, should prove useful in future N2O research.
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Department of Psychology, Marquette University, Milwaukee, WI 53233.
Green
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D000704:Analysis of Variance; D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D003624:Darkness; D005106:Exploratory Behavior / Q000187:drug effects*; D008027:Light; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D009609:Nitrous Oxide / Q000494:pharmacology*; D011600:Psychopharmacology / Q000295:instrumentation*
D014151:Anti-Anxiety Agents; D009609:Nitrous Oxide