Rothmanet al (1991) Labelling by [3H]1,3-di(2-tolyl)guanidine
of two high affinity binding sites in guinea pig brain: evidence for allosteric
regulation by calcium channel antagonists and pseudoallosteric modulation by σ ligands. Mol.Pharmacol. 39 222. Quirion
et al (1992) A proposal for the classification of sigma binding
sites. TiPS 13 85.