ABSTRACT
INTRODUCTION Gamma-aminobutyric acid (GABA) is an amino acid neurotransmitter, first discovered more than 50 years ago (1). Approximately 30% of synapses in the vertebrate central nervous system have been show to contain GABA, making it the most abundant inhibitory neurotransmitter. Consequently it is not surprising that GABAergic neurotransmission plays a key role in the normal physiological function of the brain, including sleep regulation (2-5), as well as various pathophysiological sequelae (6). GABA receptors have traditionally been classified according to pharmacological criteria into three groups, GABAA, GABAB and GABAC receptors. GABAA and GABAC receptors are ligand-gated ion channels whereas GABAB receptors are G proteincoupled receptors (7). Molecular cloning studies have revealed the structural basis for this classification, a heterogeneity hitherto unrealized (particularly in the case of GABAA receptors) and that GABAC receptors should be considered part of the GABAA receptor family (7,8).
