The immunohistochemical distribution of the GABAA receptor α1, α2, α3, β2/3 and γ2 subunits in the human thalamus

The GABA_A receptor is the most abundant inhibitory receptor in the human brain and is assembled from a variety of different subunit subtypes which determines their pharmacology and physiology. To determine which GABA_A receptor subunit proteins are found in the human thalamus we investigated the distribution of five major GABA_A receptor subunits α₁, α₂, α₃, β_2,3 and γ₂ using immunohistochemical techniques. The α₁-, β_2,3- and γ₂- subunits which combine to form a benzodiazepine sensitive GABA_A receptor showed the most intense levels of staining and were the most common subunits found throughout the human thalamus especially in the ventral and posterior nuclear groups. The next most intense staining was for the α₃-subunit followed by the α₂-subunit. The intralaminar nuclear group, the mediodorsal nucleus and the thalamic reticular nucleus contained α₁-, β_2,3- and γ₂- subunits staining as well as the highest levels of the α₂- and α₃- subunits. The sensory dorsal lateral geniculate nucleus contained very high levels of α₁- and β_2,3- and γ₂-subunits. The highest densities of GABA_A receptors found throughout the thalamus which contained the subunits α₁, β_2,3, and γ₂ included nuclei which are especially involved in the control or the modulation of the cortico-basal ganglia-thalamo-cortical motor circuits and are thus important in disorders such as Huntington's disease where the GABAergic projections of the basal ganglia are compromised. In addition the majority of receptors in the thalamic reticular nucleus contain α₃ and γ₂ subunits whilst the intralaminar nuclei contain high levels of α₂ and α₃ subunits.