Brain slices in radioligand binding assays: quantification of opiate, benzodiazepines and beta-adrenergic ([3H] CGP-12177) receptors.

We have characterized and quantified specific binding of [3H]-flunitrazepam (FNZ; (benzodiazepine), [3H]-naloxone (NAL; (opiate) and [3H] CGP-12177(CGP; (beta-adrenergic) to thick slices (230-400 micron) of mouse and rat brain. The binding sites are stereospecific, saturable and of high affinity. In all cases, the binding of the ligands is readily reversible and demonstrates the appropriate drug specificity. In mouse brain [3H]-NAL binding is elevated by chronic treatment with naloxone (via capsules). We have been unsuccessful in quantifying beta adrenoreceptors with the archetypal ligand [3H]-dihydroalprenolol (DHA). However, the use of [3H]-CGP 12177 enabled us to detect high-affinity beta adrenoreceptors in brain slices. [3H]-CGP also permits the demonstration of rapid and reversible agonist-induced down-regulation (internalization) of beta binding sites. We have been successful in quantifying beta adrenergic sites in single pineal glands of rat and hamster.