Expression of 10 GABA A receptor subunit messenger RNAs in the motor-related thalamic nuclei and basal ganglia of Macaca mulatta studied with in situ hybridization histochemistry

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In situ hybridization histochemistry technique with [ 35S]UTP-labelled riboprobes was used to study the expression pattern of 10 GABA A receptor subunit messenger RNAs in the basal ganglia and motor thalamic nuclei of rhesus monkey. Human transcripts were used for the synthesis of α 2, α 4, β 2, β 3, γ 1 and δ subunit messenger RNA probes. Rat complementary DNAs were used for generating α 1, α 3, β 1 and γ 2 subunit messenger RNA probes. Nigral, pallidal and cerebellar afferent territories in the ventral tier thalamic nuclei all expressed α 1, α 2, α 3, α 4, β 1, β 2, β 3, δ and γ 2 subunit messenger RNAs but at different levels. Each intralaminar nucleus displayed its own unique expression pattern. In the thalamus, γ 1 subunit messenger RNA was detected only in the parafascicular nucleus. Comparison of the expression patterns with the known organization of GABA A connections in thalamic nuclei suggests that (i) the composition of the receptor associated with reticulothalamic synapses, except for those in the intralaminar nuclei, may be α 1 α 4 β 2 δ, (ii) receptors of various other subunit compositions may operate in the local GABAergic circuits, and (iii) the composition of receptors at nigro- and pallidothalamic synapses may differ, with those at nigrothalamic probably containing β 1 and γ 2 subunits. In the medial and lateral parts of the globus pallidus, the subthalamic nucleus and the substantia nigra pars reticularis, the α 1, β 2 and γ 2 messenger RNAs were co-expressed at a high level suggesting that this subunit composition was associated with all GABAergic synapses in the direct and indirect striatal output pathways. Various other subunit messenger RNAs were also expressed but at a lower level. In the substantia nigra pars compacta the most highly expressed messenger RNAs were α 3, α 4 and β 3; all other subunit messenger RNAs studied, except for γ 1, α 1 and α 2, were expressed at a moderate to high level. In the striatum, the following subunit messenger RNAs were expressed (listed in order of decreasing signal intensity): α 4, β 3, α 2, α 3, β 2, δ, γ 2, α 1. The expression patterns found in the monkey were similar to those described in comparable nuclei in the rat by Wisden et al. [ J. Neurosci. (1992) 12, p. 1040]; however, the monkey nuclei displayed a much greater variety of GABA A receptor subunit messenger RNAs.