E-IA-DM-PE-PIPZE (i.p.) inhibits, in dose-dependent fashion, specific in vivo binding of [125I]E-IA-DM-PE-PIPZE (2.5 μCi, i.v.) to σ receptors at 30 min in CD-1® mouse brain, heart, 1 spleen and lung (Panels A – D). ED50 values calculated from sigmoidal, unconstrained four-parameter logistic fits. Means ± SEM, n = 5.