Conditioned inhibition of cyclophosphamide-induced taste aversion.

Rats in an experimental group received trials during which 1 flavor (saccharin) was always followed by cyclophosphamide, an immunosuppressive drug, but another (vanilla) was not. An unconditioned stimulus-only group served as a control. Flavor-preference tests revealed that conditioned excitation and conditioned inhibition occurred in the conditioned group subjects but not in the control group subjects. This demonstration suggests that a conditioned inhibitor might be used to modify conditioned and unconditioned immune system functions, for example, natural killer-cell activity.