ABSTRACT
GABA(A) receptors are the major inhibitory neurotransmitter receptors in the central nervous system and are targets of clinically important drugs modulating GABA induced ion flux by interacting with distinct allosteric binding sites. ROD 185 is a previously investigated structural analogue of the GABA site antagonist bicuculline, and a positive allosteric modulator acting via the benzodiazepine binding site. Here, we investigated 13 newly synthesized structural analogues of ROD 185 for their interaction with rat GABA(A) receptors. Using [(3)H]flunitrazepam binding assays, we identified four compounds exhibiting a higher affinity for the benzodiazepine binding site than ROD 185. Two electrode voltage clamp electrophysiology at recombinant GABA(A) receptors indicated that most of these compounds positively modulated GABA-induced currents at these receptors. Additionally, these experiments revealed that this compound class not only interacts with the benzodiazepine binding site at αßγ receptors but also with a novel, so far unidentified binding site present in αß receptors. Compounds with a high affinity for the benzodiazepine binding site stimulated GABA-induced currents stronger at αßγ than at αß receptors and preferred α3ß3γ2 receptors. Compounds showing equal or smaller effects at αßγ compared to αß receptors differentially interacted with various αß or αßγ receptor subtypes. Surprisingly, five of these compounds interacting with αß receptors showed a strong stimulation at α6ß3γ2 receptors. The absence of any direct effects at GABA(A) receptors, as well as their potential selectivity for receptor subtypes not being addressed by benzodiazepines, make this compound class to a starting point for the development of drugs with a possible clinical importance.
