BENZODIAZEPINE-INDUCED GABAA RECEPTOR PLASTICITY

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The GABA inhibitory synaptic system plays a major role in the central nervous system and is implicated in human neurological and psychiatric disorders such as epilepsy, stress, anxiety and panic disorders, sleep disorders, and drug dependence, especially to benzodiazepines and ethanol. The major postsynaptic GABA receptors involved in rapid inhibitory neurotransmission are the GABA/A receptors (GABA). GABAR proteins are subject to regulation at the level of transcription, translation, assembly, cell targeting, and the functional level. Endogenous regulation includes modulation by phosphorylation, zinc ions, and neuroactive steroids. GABAR are the known target of numerous clinically relevant drugs, including anti-epileptic anti-anxiety, and sedative/hypnotic/aesthetic agents. These include the widely used benzodiazepines, barbiturates, and possibly alcohol. GABAR are widely accepted as the major candidate molecular target of general anesthetic action. Their predominant role in the brain makes GABA likely players in the normal plasticity mechanisms that accompany ordinary and extraordinary experiences. By subjecting rats, or in some cases, cells, to somewhat extraordinary experiences that are considered to involve GABAR, we will investigate whether plastic changes in GABAR occur and the molecular and cellular mechanisms of the long-term modifications. In particular, chronic exposure of rats to benzodiazepines, but probably an elevation of GABAR function, leads to tolerance, especially to the anti-epileptic actions of these drugs. Tolerance is accompanied by a reduced GABAR function, reduced enhancement of GABAR function by benzodiazepines, and uncoupling of GABA- benzodiazepine binding measured in vitro. Tolerance to benzodiazepines can be mimicked in cells expressing recombinant GABAR that lack normal transcriptional control, and can be reversed rapidly by exposure in rats and in cells by exposure to the benzodiazepine antagonist flumazenil. This strongly suggests that the tolerance and reversal result from a physicochemical modification of the GABAR protein itself. This project will attempt to unearth this molecular mechanisms of plasticity. Ultimately therapeutic strategies could be based on our studies, aimed rationally at preventing the unwanted or pathological alterations in GABA/A receptors characteristic of several neurological and psychiatric disorders.