Effect of treatments on LPS-induced expression of TNF-α mRNA and protein in the spleen (A, C) and liver (B, D) as determined by real-time RT-PCR. Re-exposure to the previously heroin-paired environment (CS, conditioned stimulus) reduced TNF-α mRNA and protein in both spleen and liver tissue and this reduction was not attenuated by inactivation of the caudate control region. The RT-PCR data (A, B) are expressed as TNF-α copy number per 10 ng cDNA based on a standard curve using Roche LightCycler software. The ELISA data (C, D) are expressed as picograms of protein per ml. (*) Asterick indicates a significant difference (p<0.05) from the HC (Home cage), Saline-Caud group.