The interaction of substituted benzamides with brain benzodiazepine binding sites in vitro

1 The interaction of substituted benzamides with brain benzodiazepine (BDZ) binding sites was examined by their ability to displace [3H]‐flunitrazepam ([3H]‐FNm) from specific binding sites in bovine cortical membranes in vitro. 2 Clebopride, Delagrange 2674, Delagrange 2335 and BRL 20627 displayed concentration‐dependent displacement of [3H]‐FNM with IC50 values of 73 nM, 132 nM, 7.7 μm and 5.9 μm, respectively. Other substituted benzamides including metoclopramide, sulpiride, tiapride, sultopride and cisapride were inactive at 10−5 m. 3 Inhibition by clebopride and Delagrange 2674 of [3H]‐FNM binding was apparently competitive and readily reversible. 4 In the presence of γ‐aminobutyric acid (GABA), the ability of diazepam and Delagrange 2674 to displace [3H]‐Ro 15–1788 binding was increased 3.6 and 1.6 fold respectively, compared to the absence of GABA, while ethyl β‐carboline‐3‐carboxylate (βCCE) and clebopride were less potent in the presence of GABA. 5 Diazepam was 30 fold less potent at displacing [3H]‐Ro 15–1788 in membranes that had been photoaffinity labelled with FNM than in control membranes, whereas the potency of βCCE did not differ. Clebopride and Delagrange 2674 showed a less than two fold loss of potency in photoaffinity labelled membranes. 6 The pattern of binding of clebopride and Delagrange 2674 in these in vitro tests is similar to that found previously with partial agonists or antagonists at BDZ binding sites. 7 Clebopride and Delagrange 2674 inhibited [3H]‐FNM binding with similar potency in rat cerebellar and hippocampal membranes, suggesting they have no selectivity for BDZ1 and BDZ2 binding sites. 8 Clebopride and Delagrange 2674 are structurally dissimilar to other BDZ ligands and represent another chemical structure to probe brain BDZ binding sites.