?-Carboline binding indicates the presence of benzodiazepine receptor subclasses in the bovine central nervous system

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Abstract
Receptor binding studies were performed with tritiated propyl β-carboline-3-carboxylate ([3H]PrCC), tritiated ethyl β-carboline-3-carboxylate ([3H]ECC), and tritiated flunitrazepam ([3H]FNT) in membrane preparations from different regions of the bovine brain and retina. Specific binding in all regions investigated was associated with benzodiazepine receptor sites. However, not all benzodiazepine receptor sites. However, not all benzodiazepine receptors in the regions investigated as determined by the specific binding of tritiated flunitrazepam ([3H]FNT) are available for [3H]PrCC suggesting that specific [3H]PrCC binding labels only one subclass or subpopulation of the benzodiazepine receptor. This benzodiazepine receptor subclass is sensitive to GABAergic modulation and amounts for about 60% of the benzodiazepine receptors in bovine cortex, hippocampus, and retina but for about 80% of the benzodiazepine receptors in the bovine cerebellum. By contrast, specific [3H]ECC binding in the cerebellum and the hippocampus labeled the same number of benzodiazepine receptors as [3H]FNT, giving no evidence for a benzodiazepine receptor subclass specificity of this compound in the bovine CNS.