clozapine and preclamol

Aripiprazole and the candidate antipsychotics, S33592, bifeprunox, N-desmethylclozapine (NDMC) and preclamol, are partial agonists at D(2) receptors. Herein, we examined their actions at D(2L) and D(3) receptors expressed separately or together in COS-7 cells. In D(2L) receptor-expressing cells co-transfected with (D(3) receptor-insensitive) chimeric adenylate cyclase-V/VI, drugs reduced forskolin-stimulated cAMP production by approximately 20% versus quinpirole (48%). Further, quinpirole-induced inhibition was blunted by aripiprazole and S33592, confirming partial agonist properties. In cells co-transfected with equal amounts of D(2L)and D(3) receptors (1 : 1), efficacies of aripiprazole and S33592 were attenuated. Further, in cells co-transfected with D(2L) and an excess of D(3) receptors (1 : 3), aripiprazole and S33592 were completely inactive, and they abolished the actions of quinpirole. Likewise, bifeprunox, NDMC and preclamol lost agonist properties in cells co-transfected with D(2L)and D(3) receptors. Accordingly, at split D(2trunk)/D(3tail) and D(3trunk)/D(2tail) chimeras, agonist actions of quinpirole were blocked by aripiprazole and S33592 that, like bifeprunox, NDMC and preclamol, were inactive alone. Conversely, when a 12 amino acid sequence in the third intracellular loop of D(3) receptors was replaced by the homologous sequence of D(2L) receptors, aripiprazole, S33592, bifeprunox, NDMC and preclamol inhibited cAMP formation by approximately 20% versus quinpirole (42%). Moreover, at D(2L) receptor-expressing cells co-transfected with modified D(3i3(D2)) receptors, drugs behaved as partial agonists. To summarize, low efficacy agonist actions of aripiprazole, S33592, bifeprunox, NDMC and preclamol at D(2L) receptors are abrogated upon co-expression of D(3) receptors, probably due to physical association and weakened coupling efficacy. These findings have implications for the functional profiles of antipsychotics.

Topics: Adenylyl Cyclases; Animals; Antipsychotic Agents; Aripiprazole; Benzamides; Benzoxazoles; Carrier Proteins; Chlorocebus aethiops; Clozapine; COS Cells; Cricetinae; Dopamine Agonists; Dopamine Antagonists; Dose-Response Relationship, Drug; Drug Interactions; Piperazines; Piperidines; Quinolones; Receptors, Dopamine D2; Receptors, Dopamine D3; Transfection

The antipsychotic drugs have been shown to be inverse agonists at the D(2) dopamine receptor. We have examined the mechanism of this inverse agonism by making mutations in residue T343 in the base of the sixth transmembrane spanning region of the receptor. T343R, T343S and T343K mutant D(2) dopamine receptors were made and the T343R mutant characterized in detail. The T343R mutant D(2) dopamine receptor exhibits properties of a receptor that resides more in the activated state, namely increased agonist binding affinity (independent of G-protein coupling and dependent on agonist efficacy), increased agonist potency in functional tests (adenylyl cyclase inhibition) and increased inverse agonist effects. The binding of agonists to the mutant receptor also shows sensitivity to sodium ions, unlike the native receptor, so that isomerization of the receptor to its inactive state may be driven by sodium ions. The binding of inverse agonists to the receptor is, however, unaffected by the mutation. We conclude that inverse agonism at this receptor is not achieved by the inverse agonist binding preferentially to the non-activated state of the receptor over the activated state. Rather the inverse agonist appears to bind to all forms of the receptor but then renders the receptor inactive.

Topics: 1-Methyl-3-isobutylxanthine; 8-Hydroxy-2-(di-n-propylamino)tetralin; Animals; Antipsychotic Agents; Apomorphine; Binding, Competitive; Bromocriptine; Butaclamol; Chlorpromazine; CHO Cells; Clozapine; Colforsin; Cricetinae; Cricetulus; Cyclic AMP; Dopamine Agonists; Dopamine Antagonists; Dopamine D2 Receptor Antagonists; Dose-Response Relationship, Drug; GTP-Binding Proteins; Haloperidol; Humans; Macromolecular Substances; Mutagenesis, Site-Directed; Phenethylamines; Piperidines; Protein Binding; Protein Conformation; Radioligand Assay; Receptors, Dopamine D2; Recombinant Fusion Proteins; Sodium; Spiperone; Structure-Activity Relationship; Sulpiride; Transfection; Tyramine

1. Male CD-1 mice were tested for prepulse inhibition (PPI) following administration of PCP and the PCP site ligand, (+)MK-801, as well as the dopamine (DA) agonist (-)-apomorphine and DA releaser d-amphetamine. Similar to reports in rats, PCP (0.36-36.0 mumol/kg), (+)MK-801 (0.03-3.0 mumol/kg), (-)-apomorphine (3.3 and 10.0 mumol/kg) and d-amphetamine (3.0 and 8.0 mumol/kg) significantly reduced PPI when administered prior to testing. 2. Because PCP also binds to sigma receptors, the authors tested the sigma ligand (+)-3-PPP at (118 mumol/kg) which marginally increased the PPI. 3. Haloperidol (1.1 mumol/kg) pretreatment attenuated the reduction in PPI following (-)-apomorphine (10.0 mumol/kg), however no effects of haloperidol or clozapine pretreatment on (+)MK-801 disruption of PPI were observed. 4. Because of the pharmacological similarities between mouse data and previously published rat data, it is concluded that the mouse is a viable alternative to the rat for testing PPI.

Topics: Acoustic Stimulation; Animals; Apomorphine; Clozapine; Dextroamphetamine; Dizocilpine Maleate; Dopamine Agonists; Dose-Response Relationship, Drug; Haloperidol; Male; Mice; Mice, Inbred Strains; Phencyclidine; Piperidines; Rats; Receptors, sigma; Reflex, Startle; Species Specificity

The actions in vitro of SCH 23390, YM 09151-2 and both enantiomers of 3-PPP on D-1 and D-2 dopamine receptors were investigated in superfused rat neostriatal slices. For comparison the following neuroleptics of different chemical classes were incorporated in our investigations: (+)-bulbocapnine, clozapine, chlorpromazine, cis-flupenthixol, (-)-sulpiride and haloperidol. The increase in the efflux of cyclic AMP was used as a measure for D-1 receptor stimulation. The decrease in the K+-evoked release of [3H]acetylcholine was used as measure of D-2 receptor stimulation. None of the drugs stimulated the D-1 receptor. Only (+)-3-PPP stimulated the D-2 receptor. All other drugs, including (-)-3-PPP, behaved as antagonists on the D-2 receptor, YM 09151-2 being the most potent. SCH 23390 was the most potent antagonist on the D-1 receptor. Haloperidol, cis-flupenthixol and (+)-bulbocapnine showed an appreciable D-1 receptor blocking potency in our model, whereas the other drugs were inactive. We found SCH 23390 to be the most D-1 selective antagonist although the drug still displayed considerable potency on the D-2 receptor. YM 09151-2 was the most D-2 selective antagonist.

Topics: 1-Methyl-3-isobutylxanthine; Acetylcholine; Animals; Antipsychotic Agents; Aporphines; Benzamides; Benzazepines; Caudate Nucleus; Chlorpromazine; Clozapine; Flupenthixol; Haloperidol; In Vitro Techniques; Male; Piperidines; Potassium; Putamen; Rats; Rats, Inbred Strains; Receptors, Dopamine; Receptors, Dopamine D1; Receptors, Dopamine D2

Several novel dopamine (DA) agonists (SKF 38393, 3-PPP, TL-99) have been reported to induce rotational behavior (RB) in rats unilaterally denervated of the nigro-striatal pathway by 6-hydroxydopamine. Other reports have indicated no RB, however, and these drugs do not cause other behavioral manifestations of postsynaptic DA agonism. In the present experiments, two groups of 6-hydroxydopamine-denervated rats were distinguished by their relative responsiveness to apomorphine-induced RB. A highly sensitive group showed maximal RB in response to doses as low as 0.03 mg/kg, while a less sensitive group exhibited comparable RB only in response to 15- to 20-fold higher doses. The high sensitivity group exhibited RB in response to SKF 38393, 3-PPP and pergolide, but the low sensitivity group did not show appreciable RB after these drugs, even at doses 50 to 100-fold higher. Haloperidol markedly attenuated apomorphine-induced RB in the low sensitivity subgroup, but only reduced by approximately one-half the number of turns induced by apomorphine or SKF 38393 in the high sensitivity group. The atypical antipsychotics, clozapine and RMI 81582, and the muscle relaxant, methocarbamol, reduced RB in all groups, but only at doses that caused performance impairment in a rotorod test. These results appear to reflect qualitative differences in responsiveness to different DA agonists. Behavioral preselection of 6-hydroxydopamine-denervated animals is necessary to achieve consistent pharmacological results with the 6-hydroxydopamine RB model.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Animals; Apomorphine; Benzazepines; Clozapine; Ergolines; Humans; Hydroxydopamines; Male; Oxidopamine; Pergolide; Piperidines; Postural Balance; Rats; Rats, Inbred Strains; Receptors, Dopamine; Stereotyped Behavior; Sympathectomy, Chemical