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

Abstract 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 α 1 , α 2 , α 3 , β 2,3 and γ 2 using immunohistochemical techniques. The α 1 -, β 2,3 - and γ 2 - 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 α 3 -subunit followed by the α 2 -subunit. The intralaminar nuclear group, the mediodorsal nucleus and the thalamic reticular nucleus contained α 1 -, β 2,3 - and γ 2 - subunits staining as well as the highest levels of the α 2 - and α 3 - subunits. The sensory dorsal lateral geniculate nucleus contained very high levels of α 1 - and β 2,3 - and γ 2 -subunits. The highest densities of GABA A receptors found throughout the thalamus which contained the subunits α 1 , β 2,3 , and γ 2 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 α 3 and γ 2 subunits whilst the intralaminar nuclei contain high levels of α 2 and α 3 subunits.