GABA (γ-aminobutyric acid) is the major inhibitory neurotransmitter in the brain. Its production, release, reuptake, and metabolism all occur in the nervous system.nThe GABA transmitter interacts with two major types of receptors: ionotropic GABAA receptors (GABAAR) and metabotropic receptors (GABABR). GABAARs belong to the ligand-gated ion channel superfamily. GABA inhibits the activity of signal-receiving neurons by interacting with the GABAA receptor on these cells3. Binding of GABA to its GABAA receptor results in conformational changes that open a Cl- channel, producing an increase in membrane conductance that results in inhibition of neural activity.nGABAARs are heteropentamers, in which all five subunits contribute to the pore formation. To date, eight subunit isoforms have been cloned: α, β, γ, δ, ε, π, θ, and ρ1. Six α subunit isoforms have been found to exist in mammals (α1-α6). In most cases, native GABAA receptors consist of 2α, 2β, and 1γ subunits. The α subunit is the most common and is expressed ubiquitously. It determines the affinity of GABAARs for allosteric ligands.nEach subtype has a unique regional expression in the brain, and individual neurons often express multiple subtypes4. For example, the α4 subunit is detected in the hippocampus, cortex, olfactory bulb and in the basal forebrain. ATTO dyes are characterized by strong absorption (high extinction coefficient), high fluorescence quantum yield, and high photo-stability. ATTO 633 has a maximum absorption at 629 nm and a maximum fluorescence at 657 nm. The fluorescence is excited most efficiently in the range 610 to 645 nm. This label is analogous to the well-known dyes Alexa 647, Alexa 633 and Cy5.