Nitrous oxide: sensory, motor, associative, and behavioral tolerance effects in classical conditioning of the rabbit nictitating membrane response.

Experiment 1, of a series of six experiments with the rabbit nictitating membrane response (NMR) preparation, revealed that nitrous oxide (0%, 33%, 67%) impaired acquisition of conditioned responses (CRs). Subsequent experiments indicated that nitrous oxide (N2O) had no reliable effects upon nonassociative processes (Experiment 2); impaired unconditioned response (UR) amplitude (Experiment 3); attenuated tone-conditioned stimulus (CS) intensity (Experiment 4); decremented tone-induced reflex modification of the unconditioned NMR (Experiment 5); and demonstrated no reliable evidence of behavioral tolerance (Experiment 6). It was concluded that N2O's impairment of CR acquisition was attributable to its attenuation of the intensity of tone CSs and shock USs and/or UR amplitude. These findings are consistent with the behavioral laws of conditioning: the attenuation of the intensive sensory properties of the CS and US and/or UR components of conditioning affect their ability to enter into the establishment of CS-CR connections and, therefore, the development of associative learning.