Autoradiographic localization of sigma opioid receptors in the gastrointestinal tract of the guinea pig

The distribution of σ and phencyclidine binding sites in the gastrointestinal tract of the guinea pig was studied by autoradiography after in vitro incubation of tissue slices with (+)3H-SKF 10,047 and 3H-1-1-[(2-thienyl)cyclohexyl] piperidine to locate σ and phencyclidine receptors, respectively. A dense distribution of σ binding sites was observed in the mucosa and in the submucosal plexus, particularly at the level of the fundus and duodenum. Muscular layers were only marginally labeled. No phencyclidine binding site could be demonstrated in any area. This selective distribution suggests a functional role of σ receptors mainly in the control of endocrine or exocrine secretions, or both.