Gamma-aminobutyric acid (GABA) is the primary inhibitory neurotransmitter in the central nervous system, causing a hyperpolarization of the membrane through the opening of a Cl? channel associated with the GABA A Receptor (GABA A-R) subtype. GABA A-Rs are important therapeutic targets for a range of sedative, anxiolytic, and hypnotic agents and are implicated in several diseases including epilepsy, anxiety, depression, and substance abuse. The GABA A-R is a multimeric subunit complex. To date six as, four bs and four gs, plus alternative splicing variants of some of these subunits, have been identified (Olsen and Tobin, 1990; Whiting et al., 1999; Ogris et al., 2004). Injection in oocytes or mammalian cell lines of cRNA coding for a- and b-subunits results in the expression of functional GABA A-Rs sensitive to GABA. However, co-expression of a g-subunit is required for benzodiazepine modulation. The various effects of the benzodiazepines in brain may also be mediated via different a-subunits of the receptor (McKernan et al., 2000; Mehta and Ticku, 1998; Ogris et al., 2004; P