Benzodiazepine receptor in brain

Kinetics of clonazepam in relation to electroencephalographic and clinical effects

The aim of this study was to see if the immediate EEG and clinical response to an intravenous dose of clonazepam was predictive for the effect of oral clonazepam maintenance therapy. Four children with petit mal epilepsy were given clonazepam intravenously during continuous EEG recording. Clonazepam plasma concentrations were determined repeatedly with a high performance liquid chromatographic method using a reversed phase system. The day after the intravenous dose the patients were given oral therapy with clonazepam. Repeated long-term EEG recordings were made and plasma concentrations of clonazepam were determined. There was no clinically satisfactory effect of clonazepam during oral maintenance treatment in three of the children who responded well to the intravenous dose of clonazepam. Thus, the immediate response to intravenous clonazepam was not a good predictor of the long-term effects in our patients.

Development and differentiation of the benzodiazepine receptor in cultures of fetal mouse spinal cord

Cultures of fetal mouse spinal cord were assayed for the development of the benzodiazepine (BDZ) receptor on intact cells in situ. At 2 and 3 weeks in culture, levels of binding were low and Scatchard analysis was linear revealing a single binding site with Kds of 115 and 71 nM, respectively. After 4 weeks in culture, coincident with large increases in neuronal (clonazepam displaceable) and nonneuronal (Ro5-4864 displaceable) binding. Scatchard plots became non-linear revealing 2 distinct binding sites with Kds of 11 and 175 nM.

Retinal benzodiazepine receptors are destroyed by kainic acid lesions

[3H]Diazepam binds to preparations of membranes from chicken retina. Two binding sites were detected; a high affinity site (KD, 1.8 nM and Bmax, 0.17 pmol/mg retina protein) and a low affinity site (KD, 132 nM and Bmax, 1.46 pmol/mg retinal protein). GABA stimulated [3H]diazepam binding to these retinal membranes. One week after injection of kainic acid into the eye, which destroys the horizontal and amacrine cells of the retina, the low affinity site disappeared, while the level of the high affinity site was hardly affected. These results establish that chicken retina contains benzodiazepine receptors, which are closely associated with GABA receptors. The benzodiazepine receptors are probably associated with horizontal and/or amacrine cell synapses which use GABA as a transmitter.

Brain specific benzodiazepine receptors

Brain membranes from rat and human contain a single class of brain specific binding sites for pharmacologically and clinically active benzodiazepines. There is good correlation between the pharmacological effects of benzodiazepines and the affinity for the 3H-diazepam binding site. Benzodiazepine binding sites are not present on glial cells. Selective neuronal degeneration experiments in rats indicate a neuronal localization. 3H-Flunitrazepam is a very suitable ligand for affinity binding and it binds to the same class of binding sites as 3H-diazepam. Our results indicate that the in vitro 3H-diazepam and 3H-flunitrazepam binding sites are the receptors which in vivo mediate various pharmacological and clinical effects of benzodiazepines.