Behaviorally conditioned immunosuppression with cyclosporine A forms long lasting memory trace.

Behaviorally conditioned taste avoidance (CTA) paradigms using the novel taste saccharin as a conditioned stimulus (CS) and the immunosuppressive drug cyclosporine A (CsA) as unconditioned stimulus (US) demonstrate learned suppression of immune functions. However, conditioned immune responses might decrease over time depending on the period between acquisition and retrieval (retention interval). Thus, the present study investigated whether and to what extent prolonged 14- and 30-days retention intervals affect conditioned behavioral (CTA) and immune responses in rats. Our findings demonstrate that conditioned animals displayed a marked CTA after 14 and 30 days upon CS re-exposure compared to control animals. More importantly, the production of the pro-inflammatory cytokine interferon (IFN)-γ was significantly suppressed in ex vivo anti-CD3 stimulated splenocytes of conditioned animals compared to controls at both time points. These findings document that CTA paradigms using the immunosuppressive drug CsA as US form long lasting memory traces of the learned behavioral and immune responses.