Effects of dopamine receptor agonist and antagonists on cholestasis-induced anxiolytic-like behaviors in rats.

Dysfunctions in the dopamine transmission system have been suggested to contribute to the pathogenesis of hepatic encephalopathy. In an experimental animal model, cholestasis induction through bile duct ligation may present several main pathological features of hepatic encephalopathy. Dopaminergic systems are shown to play pivotal roles in regulation of anxiety-like behaviors. The main bile duct in male Wistar rats, weighing 220-240 g, was ligated using two ligatures plus duct transection in between. Anxiety-like behaviors were measured using the elevated plus maze task. Cholestasis increased the open arm time percentage (%OAT), 13 but not 10 days after bile duct ligation, indicating an anxiolytic-like effect. Sole intraperitoneal injection of apomorphine (dopamine D1/D2 receptor agonist, 0.25 mg/kg), SCH23390 (dopamine D1 receptor antagonist, 0.005, 0.01 and 0.02 mg/kg) or sulpiride (dopamine D2 receptor antagonist, 0.125, 0.25 and 0.5 mg/kg) did not alter %OAT, open arm entries percentage (%OAE) and locomotor activity in the sham-operated rats. Meanwhile, the higher dose apomorphine (0.5 mg/kg) induced anxiolytic-like behaviors in this group. The subthreshold dose injection of SCH23390 or sulpiride, partially reversed the anxiolytic-like behaviors induced by cholestasis (13 days after bile duct ligation). On the other hand, subthreshold dose of apomorphine in cholestatic rats (10 days post bile duct ligation) induced anxiolytic-like effects which could be blocked by SCH23390 or sulpiride. The effective doses of above drugs did not alter locomotor activity, number of rearings, groomings and defections. These findings suggested that the dopaminergic system may potentially be involved in the modulation of cholestasis-induced anxiolytic-like behaviors in rats.

Association of monoamine oxidase B and catechol-O-methyltransferase polymorphisms with sporadic Parkinson's disease in an Iranian population.

Genetic polymorphisms have been shown to be involved in dopaminergic neurotransmission. This may influence susceptibility to Parkinson's disease (PD). We performed a case-control study of the association between PD susceptibility and a genetic polymorphism of MAOB and COMT, both separately and in combination, in Iranians. The study enrolled 103 Iranian patients with PD and 70 healthy individuals. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) methods were used for genotyping. Our data indicated that the MAOB genotype frequencies in PD patients did not differ significantly from the control group. However, the frequency of MAOB GG genotype was significantly lower in female patients. It has been shown that the distribution of MAOB allele A was slightly higher in PD patients. No statistically significant differences were found in the COMT allele and genotype distribution in PD patients in comparison to the controls. The combined haplotype of the MAOB A, A/A and COMT LL genotype showed a slight increase in the risk of PD in female patients in this Iranian population. The data may suggest that the MAOB and COMT genetic polymorphisms do not play any role in the pathogenesis of PD in Iranians. In addition, the combined haplotype of MAOB and COMT genes did not significantly affect the susceptibility to PD. Future studies involving larger control and case populations will undoubtedly lead to a more thorough understanding of the role of the polymorphisms involved in the dopamine pathway in PD.