Diazepam receptor: specific nuclear binding of [3H]flunitrazepam.

Area of Science:

• Neuroscience
• Biochemistry
• Pharmacology

Background:

• Benzodiazepines, like flunitrazepam, are known to bind to specific sites in the central nervous system.
• Previous studies suggested benzodiazepine binding primarily occurs at synaptic membranes.

Purpose of the Study:

• To biochemically confirm and characterize the specific binding of [3H]flunitrazepam to nuclei of the rat cerebral cortex.
• To compare the binding characteristics of [3H]flunitrazepam at nuclear and synaptosomal membrane sites.

Main Methods:

• Autoradiography was used for initial localization of [3H]flunitrazepam.
• Biochemical analysis of highly purified rat cerebral cortex nuclei was performed to quantify specific binding.
• Binding affinities (Kd(app)) and inhibition studies with inosine and hypoxanthine were conducted.

Main Results:

• Specific binding of [3H]flunitrazepam to purified rat cerebral cortex nuclei was demonstrated.
• The apparent dissociation constant (Kd(app)) for nuclear binding was 28 nM, compared to 1.1 nM for synaptosomal membranes.
• Inosine and hypoxanthine showed greater inhibition of nuclear binding than of synaptic membrane binding.

Conclusions:

• Specific binding of [3H]flunitrazepam occurs at both nuclear and synaptic membrane levels in the rat cerebral cortex.
• Different endogenous ligands likely compete for binding at these distinct sites.
• The findings suggest a possibility of ligand complex translocation between membrane and nuclear sites.