GABAA receptors convey the majority of synaptic inhibition in the CMS, the process by which excitation of a presynaptic interneuron prevents the excitation of a postsynaptic principal neuron. GABAA receptors also are important therapeutic targets for benzodiazepines and general anesthetics. Receptor function is also modulated by neurosteroids and many abused hypnotic drugs. Mutations in GABAA receptor genes have been linked to familial epilepsies, schizophrenia and autism. However, it is not known how these chemicals modulate receptor function or how these mutations contribute to receptor dysfunction or disease pathology at the molecular level. The receptor functions as a chemical to voltage transducer, converting inhibitory chemical signals into hyperpolarizing membrane potentials in a wide variety of neuronal cell types throughout the nervous system. When the amplitude, duration or timing of these inhibitory signals is altered either by drug or disease, the function of the CMS is profoundly altered. The underlying hypothesis of this work is that specific amino acids in the GABAA receptor b subunit define a novel allosteric coupling pathway in the GABAA receptor. The goals of this project are i) to characterize a new binding site on the receptor and ii) to better understand the molecular events that underpin the activation and modulation of fast inhibitory neurotransmission. Using the modern molecular pharmacologic tools of patch-clamp electrophysiology, site directed mutagenesis, kinetic and structure homology modeling, we have novel positions in the b subunit that are critical for the allosteric activation of the protein that precedes channel opening and for the modulation of channel activity by neuroactive chemicals. The results generated in these studies will represent a large step forward in understanding drug action on ligand-gated channels. Furthermore, these results may aid in understanding how inherited mutations in GABAA receptor genes contribute to the pathogenesis of diseases such as schizophrenia, autism and epilepsy. Finally, it is hoped that the characterization of the new modulatory binding site will provide us with a new target for treating neuropsychiatric diseases.
