The high degree of homology between the dopamine receptors has complicated the development of selective radioligands and antibodies capable of defining the localization of dopamine receptor subtypes. In particular for the receptors belonging to the same family (D1- or D2-like), the radioligands available have poor selectivity. Hence for D1 and D5 receptors the two currently known radioligands are [3H]SCH 23390 and [125I]SCH 23982. These ligands can be used for the labelling of both receptors. The D2-like receptors (D2, D3, and D4) also share common radioligands. These include [3H]nemonapride and [3H]spiperone. However, some radioligands like [3H]raclopride and [3H]PD128907 can distinguish between D2/D3 and D4 receptors.
Several specific antibodies that recognize the different subtypes of dopamine receptors are now available. Antibodies selective for D1 (MoraFerrer et al. 1997; Luedtke et al. 1999), D2 (Fishburn etal. 1994; Khan etal. 1998), D3 (Ariano and Sibley 1994), D4 (Ariano etal. 1997; Defagot etal. 1997; Lanau etal. 1997) and D5 (Bergson etal. 1995; Khan etal. 2000) receptors have been described. These antibodies have been primarily used to histochemically localise the different subtypes of dopamine receptors, but also to identify regions of the receptors involved in the interaction of dopamine receptor with G proteins (Neve et al. 1997). Below is a summary of the localization data currently available on dopamine receptor subtypes.
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