A Quantitative Autoradiographic Study of GABAA and Benzodiazepine Receptors in the Brain of the Frog, Rana esculenta

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Abstract
Specific binding sites for GABAA and benzodiazepines were detected in the brain of the frog Rana esculenta after the in vitro incubation of tissue sections with their respective specific agonists [3H] muscimol and [3H] flunitrazepam. Conditions for the binding assay were optimized and as a result binding was saturable and specific. Quantitative autoradiographic receptor measurements in the different brain sections showed that elevated levels of [3H] muscimol binding sites were found in the two layers of the cerebellum (periventricular and external) with the highest binding densities being detected in the periventricular layer. Relatively high densities of [3H] muscimol binding sites were also observed in the torus semicircularis of the mesencephalon and in the thalamic nucleus rotundus and posterolateral nucleus, plus the mitral cell layer of the olfactory bulb, the amygdala pars lateralis and the striatum of the telencephalon. Intermediate to low binding levels were obtained in the remaining brain areas such as the external layer of the optic tectum, the dorsomedial and dorsolateral anterior thalamic nuclei, the medial and lateral pallium, the medial septal nucleus, the preoptic nucleus, the dorsal and ventral infundibular nuclei of the hypothalamus and the interpeduncular nucleus. Autoradiographic evaluation of benzodiazepine receptors revealed that binding levels of [3H] flunitrazepam were overall lower than those of the GABAA sites. In fact the highest [3H] flunitrazepam binding levels were observed in the striatum, external layer of the optic tectum and the torus semicircularis.(ABSTRACT TRUNCATED AT 250 WORDS)

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