Differential inhibition of brain specific [3H]flunitrazepam binding by several types of dyes

Congo red and protein aggregation in neurodegenerative diseases

Congo red is a commonly used histological dye for amyloid detection. The specificity of this staining results from Congo red's affinity for binding to fibril proteins enriched in beta-sheet conformation. Unexpectedly, recent investigations indicate that the dye also possesses the capacity to interfere with processes of protein misfolding and aggregation, stabilizing native protein monomers or partially folded intermediates, while reducing concentration of more toxic protein oligomers. Inhibitory effects of Congo red upon amyloid toxicity may also range from blockade of channel formation and interference with glycosaminoglycans binding or immune functions, to the modulation of gene expression. Particularly, Congo red exhibits ameliorative effect in models of neurodegenerative disorders, such as Alzheimer's, Parkinson's, Huntington's and prion diseases. Another interesting application of Congo red analogues is the development of imaging probes. Based on their small molecular size and penetrability through blood-brain barrier, Congo red congeners can be used for both antemortem and in vivo visualization and quantification of brain amyloids. Therefore, understanding mechanisms involved in dye-amyloidal fibril binding and inhibition of aggregation will provide instructive guides for the design of future compounds, potentially useful for monitoring and treating neurodegenerative diseases.

[3H]-Flunitrazepam binding in the presence of beta-phenylethylamine and its metabolites

It has recently been reported that the concentration of beta-phenylethylamine (PEA) was elevated in the plasma of an individual experiencing convulsions because of an overdose of tranylcypromine. Also, high concentrations of PEA, injected into mice, were reported to induce convulsions. This convulsive effect was prevented by pretreatment with the benzodiazepines diazepam and chlordiazepoxide. In this study, PEA in concentrations from 0.5 to 100 microM failed to alter the binding of [3H]-flunitrazepam ([3H]-FLU) in membrane preparations from mouse rostral forebrain. The metabolites of PEA: phenylacetic acid, phenylethanolamine, octopamine and tyramine, also failed to affect [3H]-FLU binding. This suggests that although there are substances that act as convulsants by interacting with the benzodiazepine receptor sites, the convulsant effect of PEA and its metabolites is mediated elsewhere.

Benzodiazepine receptor multiplicity

Receptors for gamma-aminobutyric acid (GABA) are phylogenetically old and extensive GABA receptor multiplicity had already evolved in invertebrate species. High affinity, "brain specific", benzodiazepine (BZ) receptors, present in the central nervous systems of virtually all vertebrate species, represent a heterogeneous sub-class of GABA receptors. Functional GABA-BZ-ion receptor complexes are aggregates consisting of different kinds of sub-units which are probably coded for by separate genes. These sub-units may be combined in different ways to yield different benzodiazepine receptor complexes. Different GABA-BZ-ion receptor complexes probably subserve different physiological functions and more selective drugs modifying these functions will probably be found.