Signalling via rat dopamine D2-receptors expressed in mouse fibroblasts is not influenced by compounds binding to the sigma sites of these cells.

The mouse fibroblast cell line LZR-1 is a well-established test system used to characterize the intrinsic activity of dopamine D2-receptor ligands (Neve et al., Mol. Pharmac., 1989). This cell line is transfected with a eucaryotic expression vector containing the gene of the rat dopamine D2B-receptor (short isoform of the D2-receptor) (Bunzow et al., Nature, 1988). In addition to the expression of high levels of the rat dopamine D2-receptor, these mouse cells also express sigma binding sites. Binding affinities of BMY 14,802, DTG, haloperidol, (+)-pentazocine, (+)-3-PPP, and (+)-SKF 10,047 for the sigma binding sites as well as for the D2-dopamine receptor in membranes of LZR-1 cells were determined. Using intact LZR-1 cells, it was found that the influence of sigma ligands on signalling via the dopamine D2-receptor can be explained by their affinity for the latter receptor. Specific sigma ligands did not influence dopaminergic signal transduction in LZR-1 cells. It is therefore concluded that the LZR-1 cell is a suitable test model for determination of the intrinsic activity of dopamine D2-receptor ligands even if these compounds have affinity for sigma binding sites.

3H-TVX Q 7821: identification of 5-HT1 binding sites as target for a novel putative anxiolytic.

In order to clarify the mechanism of action of the putative nonbenzodiazepine anxiolytic TVX Q 7821 [2-(4-(4-(2-pyrimidinyl)-1-piperazinyl)butyl)-1, 2-benzisothiazol-3-(2H)one-1,1-dioxidehydrochloride], binding studies with the radio labelled compound were performed. 3H-TVX Q 7821 bound rapidly, reversibly and in a saturable manner with high affinity to calf brain structures with preference for the hippocampus (KD 1.62 nmol/l; Bmax 320 fmol/ mg protein). 3H-TVX Q 7821 binding was displaced only by 5-hydroxytryptamine and its agonists and antagonists including spiperone, but was not displaced by a variety of other neurotransmitters and drugs. The 5-HT2 receptor antagonist ketanserin was a weak displacer. The hippocampal binding sites for 3H-TVX Q 7821 were pharmacologically very similar to the 5-HT1-binding sites in this region. TVX Q 7821 is likely to be an important tool in research on functional aspects of 5-HT1 binding sites.

Brain serotonin receptors as a target for the putative anxiolytic TVX Q 7821.

In animal behavioral tests of anxiolytic efficacy, TVX Q 7821 was active and equipotent with diazepam, but did not produce muscle relaxation or anti-convulsant effects. The high affinity, specific binding of 3H-TVX Q 7821 to calf hippocampal membranes was displaced by serotonin (5-HT) but not by diazepam. Similarly, unlabeled TVX Q 7821 displaced 3H-5-HT but not 3H-flunitrazepam binding. Since ketanserin (a putative 5-HT2 ligand) was equally weak in displacing labeled 5-HT or TVX Q 7821, TVX Q 7821 may preferentially bind to 5-HT1, receptors.