The GABA A neurotransmitter receptor exists on most, if not all neurons. It is the site of action of the psychoactive barbiturates and benzodiazepines, which are drugs subject to abuse. The ubiquitous distribution of the receptor in the brain leads to its involvement in nearly every aspect of brain function Pharmacological and physiological evidence suggests that multiple subtypes of GABA A receptors exist. Twelve GABA A CDNAS encoding homologous (40-70%) proteins have been isolated. Receptor subtypes corresponding to native receptor subtypes can be expressed upon transfection of mammalian cells with specific CDNAS. Receptors assembled after transfection of mammalian cells with specific GABA A genes have the pharmacological specificities of GABA A receptor subtypes previously characterized in brain tissue. The finding that native receptor subtypes are the products of separate genes suggests that different receptor subtypes are responsible for particular aspects of the behavioral actions of barbiturates and benzodiazepines. In relation to that overall concept, two specific hypotheses are proposed and will be tested. I) The first hypothesis to be tested is that long term drug treatment specifically effects the ratio of expression of specific GABA A receptor subunit genes. Initial studies will concentrate on changes in alpha subunits. Such changes would result in receptors with different sensitivities to GABA , benzodiazepines and barbiturates. Many previous studies have suggested that changes in these parameters are the physiological basis of tolerance and or dependance. Changes in gene expression could therefore explain these observations. II) The second aim is to map the molecular site of action of GABA, benzodiazepines and barbiturates. This information will be useful in understanding the action and design of drugs with lower addiction potential and side effects, perhaps based on partial agonists that currently exist. These hypothesis will be tested by; I) Quantifying of MRNA levels for each of the genes after well characterized drug treatment paradigms that are thought to cause long term changes in GABA receptors. II) Examination of the levels of the pharmacologically distinct receptor subtype by radioligand binding experiments. III) Creation of chimeric receptor molecules in which small amino acid sequence changes can be correlated with specific pharmacological and physiological effects.
