Involvement of endogenous benzodiazepine receptor ligands in brain disorders: therapeutic potential for benzodiazepine antagonists?

Many therapeutic effects of benzodiazepines are mediated by neuronal high-affinity binding sites, i.e. benzodiazepine receptors (BR), located on GABAA receptors. Recently, endogenous BR ligands have partially been identified which, as agonists, either increase or, as inverse agonists, decrease GABAergic inhibition in the brain. BR antagonists, previously described as intrinsically inactive, induce effects in animals and humans under particular circumstances emphasizing a functional relevance of endogenous BR ligands. Several brain disorders, e.g. anxiety, insomnia, epilepsy, spasticity, alcoholism, coma, dementia, may be associated with a disequilibrium of opposing endogenous BR ligands changing the excitability of neurons implicated in aforementioned diseases. It is proposed that, depending on the relative role endogenous BR ligands play in the pathophysiology of these disorders, BR antagonists might demonstrate a variable efficacy in improving their symptomatology. In fact, such therapy would restore the homeostatic balance among various endogenous BR ligands being disturbed during an illness.