AB1785P Sigma-AldrichAnti-Dopamine D3 Receptor Antibody, cytoplasmic domain

The expression of dopamine D3-subtype-receptor mRNA was analyzed in defined anatomic regions of brain obtained postmortem from patients with chronic schizophrenia and from controls. The specific amplification of D3-encoding cDNA by PCR allowed the identification of D3 mRNA expression in a wide variety of anatomic regions in both control brains and brains obtained from schizophrenic patients. However, in the parietal cortex (Brodmann areas 1, 2, 3, and 5) and motor cortex (Brodmann area 4), a selective loss of D3 mRNA expression was found in schizophrenia. A different D3 mRNA species was identified that appears to be widely expressed and that is still found in those regions of schizophrenic brains where D3 mRNA could not be detected. Compared with D3 mRNA this RNA is significantly less abundant, and at present its function (if any) is unclear. Many variables associated with either the course and/or the therapeutic management of the disease may account for the selective loss of D3 mRNA in the motor, somatosensory, and somatosensory association areas of schizophrenic brains.

Three-dimensional computer models of the rat D2, D3 and D4 dopamine receptor subtypes have been constructed based on the diffraction co-ordinates for bacteriorhodopsin, another membrane-bound protein containing seven transmembrane domains presumed to be arranged in a similar spatial orientation. Models were assembled by aligning the putative transmembrane domains of the dopamine receptors with those of bacteriorhodopsin using sequence similarities, and then superimposing these modelled alpha-helices on to the bacteriorhodopsin-derived co-ordinates. These models explore the potential hydrogen bonding, electrostatic and stacking interactions within the receptor which may be important for maintaining the conformation of these receptors, and thereby provide target sites for agonist binding. Proposed interactions between the catecholamine ligands and these receptors appear to account for the affinity, although not the specificity, of these agonist ligands for the different dopamine receptor subtypes. Such models will be useful for establishing structure-function relationships between ligands and the dopamine receptors, and may ultimately provide a template for the design of receptor-specific drugs.

Using Polymerase Chain Reaction amplification of mRNAs from several areas of rat brain we have shown the occurrence of two shorter transcripts of the dopamine D3 receptor gene, in addition to that corresponding to the D3 receptor. Cloning and sequencing of these transcripts, together with the establishment of the exon-intron organization of the D3 receptor gene, shown these transcripts to result from different processes of alternative splicing. The first transcript encodes a 100 amino acid protein, being produced by splicing of an exon whose absence deletes the third transmembrane domain and gives rise downstream to a frameshift in the open reading frame. In the second transcript, an in frame 54 bp deletion is produced by splicing occurring at an internal acceptor site, suppressing half of the second extracellular loop and a small sequence in the fifth transmembrane domain. This transcript was stably expressed in CHO cells which, however, failed to reveal any dopaminergic ligand binding activity. The functional significance and possible role of these shorter variants of the dopamine D3 receptor in cell signalling remain to be established.