The role of dopamine D3, 5-HT2A and 5-HT2C receptor variants as pharmacogenetic determinants in tardive dyskinesia in African-Caribbean patients under chronic antipsychotic treatment: Curacao extrapyramidal syndromes study IX.

Tardive dyskinesia (TD) is associated with polymorphisms of the dopamine D(3), serotonin 2A and 2C receptors (DRD3, HTR2A and HTR2C, respectively). This study investigated the possible relationship between TD and the polymorphisms Ser9Gly (DRD3), 102T>C (HTR2A), -1438G>A(HTR2A) and Cys23Ser (HTR2C) in African-Caribbean inpatients. One hundred and twenty-six patients under chronic antipsychotic treatment were genotyped. The assessment of TD was carried out with the abnormal involuntary movement scale (AIMS). The relationships between the carriership of the least frequent alleles and the respective orofaciolingual dyskinesia (TDof) (sum of the items 1-4 of the AIMS), limb-truncal dyskinesia (TDlt) (sum of items 5-7 of the AIMS) and TD (sum of items 1-7 of the AIMS) were analyzed with ANCOVA, comparing means with age as a covariate and stratification for carriers and non-carriers of the mutations. In addition, we conducted pre-planned t-tests to compare AIMS values of carriers of the combinations of alleles versus the corresponding non-carriers. In the study population, females with 9Ser carriership exhibited higher AIMS values than non-carriers. Male subjects with 9Ser carriership in combination with 23Ser or -1438A carriership exhibited higher AIMS values. In male patients also, the combination of 23Ser and -1438A carriership increased TD. The study clearly shows that the African-Caribbean population differs from the Caucasian population with regard to the association of TD with the polymorphisms studied and suggests that the association of TD with the studied polymorphisms of the 5-HT(2C) and probably of the 5-HT(2A) receptor are the result of a changed susceptibility of the patients, independent of the action of the antipsychotics on these receptors.

Possible participation of D3 and D4 dopaminergic receptors on genital reflexes induced by cocaine in paradoxical sleep deprived male rats.

Previous studies have demonstrated that paradoxical sleep deprivation (PSD) potentiates cocaine-induced genital reflexes in male rats and both D1 and D2 receptors may play a role in those effects, and to examine the possibility that such might involve other dopaminergic receptors, we investigated the effects of D3 and D4 receptor subtype antagonists on cocaine-induced reflexes in sleep-deprived rats. Separate groups of PSD rats received saline, D3 (U9919A; 0.75, 1.5 and 3 mg/kg) or D4 (L745870; 0.75, 1.5 and 3 mg/kg) antagonists prior to acute cocaine challenge. Results demonstrated that U9919A induced significant reduction in the number of animals that displayed erection and the frequency of erection at two smaller doses, while no significant difference was reported for the D4 receptor antagonist. Although our studies indicate that there is a relevant participation of D3 receptors in male sexual function, D4 receptors seem not to exert an essential role in this model.

7-OH-DPAT effects on latent inhibition: low dose facilitation but high dose blockade: implications for dopamine receptor involvement in attentional processes.

7-OH-DPAT is a dopamine D2/D3 agonist, which at low doses acts preferentially on D3 receptors but at high doses it acts on D2 and D3 receptors. The present study investigated the contribution of D3 and D2 receptors on latent inhibition (LI) by using two dose levels of 7-OH-DPAT: a low dose, 0.1 mg/kg (D3 receptor activation) and a high dose, 1.0 mg/kg, (D2/D3 receptor activation) in a conditioned emotional response (CER) paradigm. The LI Protocols included CS pre-exposure (10 or 40 CS alone trials), CER induction and a non-drug CER test phase. Additionally, the drug effects upon CER acquisition without LI were assessed using the same treatments and test environment pre-exposure protocols but without the tone CS. The effects of 7-OH-DPAT on crossing, rearing and grooming were also measured in an open field 1 day after the CER test phase. The results showed that the low dose 7-OH-DPAT treatment potentiated LI at 10 but not at 40 CS pre-exposures. The high dose 7-OH-DPAT treatment blocked LI at both the 10 and 40 stimulus pre-exposures; and it also induced hyperactivity. Thus, D3 stimulation induced by a low dose of 7-OH-DPAT can facilitate LI but these effects are contingent upon and are specific to the number of stimulus presentations. Altogether, these findings indicate that D3 stimulation can enhance attentional processes, but D2 stimulation can impair attentional processes.