Can conditioned histamine release occur under urethane anesthesia in guinea pigs?

Many clinical and experimental data have shown that learning can occur unde r general anesthesia. To clarify this possibility with respect to allergic reactions, particularly asthmatic responses, we first established classical conditioned histamine release in response to a neutral odor by using pairi ngs of the odor and an inhaled antigen for five sessions (Experiment 1) and then investigated whether conditioned histamine release into the plasma, b ronchoalveolar lavage fluid (BALF), and lung tissue, which followed such a conditioning procedure, would be produced in urethane-anesthetized guinea p igs in the presence or absence; of antigen (Experiment 2). Ovalbumin (OA) w as used as the unconditioned stimulus (US) and dimethylsulfide (DMS) served as the conditioned stimulus (CS) in both experiments. In Experiment 1, the plasma histamine levels in the conditioned group increased significantly m ore than those of the unpaired control group in response to the CS during c onsciousness. In Experiment 2 in the absence of antigen, however, no signif icant differences in the histamine levels were found regarding the groups ( DMS, triethylamine, saline, or unsensitized) or the time course (before, im mediately 5 min, and 10 min after the inhalations) during anesthesia, excep t for the finding that the histamine levels in the lung tissue specimens fr om the DMS group were significantly higher than those from the triethylamin e group. In Experiment 2 in the presence of antigen, there was a significan t increase in the plasma histamine levels after exposure to the US, irrespe ctive of the presence of the CS, however, no significant difference in the histamine levels was observed between the US and the CS+US groups. These re sults indicated that a classically CS might not induce asthmatic responses under anesthesia. (C) 2001 Elsevier Science Inc. All rights reserved.