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The effects of systemic treatment with lipopolysaccharide (LPS) on conditioned gaping in a rodent model of anticipatory nausea were examined. Stimulation of the immune system has been found to enhance, impair, or have no effect on various learning and memory tasks. The development of anticipatory nausea is formed through a classically conditioned response to a context that has been paired previously with toxin-induced nausea and/or vomiting. Rats display a distinctive conditioned gaping response when injected with a nausea-inducing drug such as LiCl. In the present study, male Long-Evans rats were injected intraperitoneally with LPS (200microg/kg) or saline (NaCl) followed 90min later by an injection of the toxin LiCl or saline before being placed in a distinctive context on four conditioning days (72h apart). On the condition test day, rats (n=6/group) were placed in the distinctive context in a drug-free state and behavioral responses were videotaped. Rats given LPS followed by LiCl were found to have significantly fewer gaping responses when compared to rats given NaCl followed by LiCl. All groups were also found to have similar levels of spontaneous ingestive behaviors suggesting that the decrease in gaping was not due to motor impairment. The present results suggest that activation of the immune system with LPS administration significantly impairs the acquisition of anticipatory nausea.

Nausea and immune function were assessed in 20 cancer patients in the hospital prior to chemotherapy and compared with assessments conducted at home. Proliferative responses to T-cell mitogens were lower for cells isolated from hospital blood samples than for home samples obtained several days earlier. Patients also experienced increased nausea in the hospital. Hierarchical multiple regression analyses indicated that decreased immune function in the hospital was not related to increased anxiety. The observed anticipatory immune suppression is consistent with the hypothesis that chemotherapy patients may develop conditioned immune suppression as well as conditioned nausea after repeated pairings of hospital stimuli with the emetic and immunosuppressive effects of chemotherapy.