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Receptor occupancy

Most drugs used for mentalDisorders function by bindingto receptors of neurotransmit-ters in brain and blocking orreinforcing their signal tranmission.

Therefore, it is possible to estimateThe effectiveness of drugs byexamining the quantity of binding to receptors.

As can be seen below, by the prescription of a radiolabeledsubstance (ligand) after taking a drug that binds to the same receptors, the drug and radiolabeled substance (ligand)compete for the receptors. Thus, the quantity of ligand binding to receptors decreases in comparison to the case ofnot taking a drug.

This degree of decrease is defined as receptor occupancy, which we use as an indicator of the quantity of binding to receptor.Therefore,we can measure the quantity of binding to specific receptors with PET, and this enables us to estimate the receptor occupancy in a living body.

 

Studies of antipsychotic drugs

Antipsychotic drugs
Antipsychotic drugs1
Antipsychotic drugs2
 

It is thought that risperidone, a drug usedfor treatment of schizophrenia, functions by blocking dopamine D2 receptors in brain. In our institute, we measured the quantity of risperidone binding to dopamineD2 receptor (receptor occupancy) using a radiolabaled substance (ligand)[11C]FLB457 (see right). We also investigated the relationship between receptor occupancy and clinical effects, and prescription methods that reduces side effects by examining temporal changes of dopamine D2 receptor occupancy after prescription.

This study method can be applied to other medications (antidepressive drugs and antianxiety drugs), and our group is investigating these in regard to serotonin transporters.

It is possible to examine the effectiveness of medications not only by blood concentration but also by direct measurement of change in receptors in brain using PET.

This, therefore, will assist in the development of better medications for patients and support investigations of prescription methods.

 
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