Characterization of the discriminative stimulus effects of nitrous oxide
VCU Scholars Compass 2014 DOI: 10.25772/1a44-n774 (opens in new tab)
Study at a glance
AI-extracted from the abstract| Characteristics | Animal discrimination study Peer reviewed |
|---|---|
| Sample size | 24 |
| Population | Mice |
| Interventions | Nitrous oxide Toluene (+)-MK-801 Ketamine Memantine Ethanol |
| Dose | 60% N2O+40% O2 |
| Duration | Daily 5 minute operant sessions; mean 38 sessions to acquire discrimination; 10 minutes N2O exposure per session |
| Keywords | Nitrous oxide Stimulus psychology Discriminative model Cognitive psychology Artificial intelligence Anesthesia |
| Citations | 1 |
| Key points | Nitrous oxide produces a discriminative stimulus that is partially shared with toluene and NMDA receptor open-channel blockers, but not with GABAA agonists, opioids, or other drugs tested. |
Abstract
Nitrous oxide (N2O) is a widely used anesthetic adjunct in dentistry and medicine that is also commonly abused. N2O alters the function of several receptors in vitro and ex vivo, however, the receptors systems underlying its abuse-related intoxicating effects are poorly understood. The goals of this dissertation were to (1) establish N2O as a discriminative stimulus, (2) characterize the temporal properties of the discriminative stimulus, (3) determine the degree of similarity between N2O and other inhalants and (4) explore the neurochemical effects responsible for the stimulus properties of N2O. Twenty-four mice were trained to discriminate 10 minutes exposure to 60% N2O+40% O2 from 100% O2 in daily 5 minute food-reinforced operant sessions. Mice acquired the discrimination in a mean of 38 sessions. N2O produced concentration-dependent full substitution for itself. Full substitution required 7 minutes of N2O exposure but the offset of stimulus effects following cessation of N2O exposure were more rapid. Varying degrees of partial substitution for N2O were engendered by abused vapors and vapor anesthetics. The aromatic hydrocarbon toluene produced the most robust substitution for N2O. One or more toluene concentrations produced full substitution for N2O in 7 of 8 subjects, suggesting that these two abused inhalants share common neurochemical mechanisms. The NMDA receptor open channel blockers (+)-MK-801, ketamine and memantine produced dose-dependent partial substitution for N2O. A competitive NMDA antagonist and NMDA glycine site antagonist did not substitute for N2O. Pretreatment with (+)-MK-801 as well as ethanol produced dose-dependent leftward shifts in the N2O concentration effect curve further suggesting some overlap in their mechanisms of action. GABAA agonists and positive allosteric modulators, opioid agonists, serotonergic agonists, nicotine, a nNOS inhibitor and the psychomotor stimulant amphetamine all failed to appreciably substitute for N2O and/or failed to alter the N2O concentration effect curve when administered prior to N2O exposure. No drug tested produced greater than 80% mean N2O-lever selection leaving open the possibility of other neurochemical contributors to the stimulus effects of N2O.