Differential, Postnatal Ontogeny of Opiate and Benzodiazepine Receptor Subtypes in Rat Cerebral Cortex: Binding Characteristics of Tifluadom and Brotizolam

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The postnatal development of 3[H] ethylketocyclazocine (EKC) binding characteristics was examined using membranes from the cerebral cortex of rats at various ages. Binding site affinity did not vary significantly between postnatal days 1 and 90. However, the apparent density of cortical binding sites increased fivefold between birth and adulthood. These results were similar to another ontogenic study of brain opiate receptor binding. Whereas EKC was equally potent as a competitor for 3[H] EKC binding in cortex from neonatal and adult rats, tifluadom was three times more potent in neonatal cortex than in adult cortex as a displacer of specific EKC binding. Brotizolam, a new thienodiazepine and a potent sedative hypnotic, also was distinctly more potent as an inhibitor of 3H-diazepam binding in neonatal rat brain cortex than in adult rat brain cortex. These results suggest that subtypes of benzodiazepine receptors, as well as some opiate receptor subtypes, exhibit different rates of postnatal development.