Tehran University Medical Journal

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The purpose of this study was investigation of effect of cholestasis on bromocriptine-induced yawning in male rats. Bromocriptine, the agonist of dopamine receptors (especially "D2"), causes yawning in male intact rats. In the present study, cholestasis was produced in male rats by surgery and ligation of common bile duct. The number of yawning induced by intraperitoneal injection of bromocriptine (11 mg/kg) was compared in cholestatic rats with sham operated and control groups. Immediately after injection of the drug and putting animals on the frame of behavioral study, the number of yawning was determined in a period of one hour. Obtained results, indicated significant difference in the number of bromocriptine-induced yawning between cholestatic rats and the other two groups. There wasn't significant difference between sham and control rats. These results indicate that some changes occur in cholestatic rats which increase sensitivity and response of dopamine receptors. Since it is proved that dopamine agonist-induced yawning is mediated via nitric oxide, and also level of nitric oxide is increased in cholestasis, it can be supposed that the mentioned response may be due to elevated level of nitric oxide. On the other hand, increased number of yawning in cholestatic rats may be due to increased level of endogenous opioids in these animals.

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Background: Dopaminergic is the most important neurotransmitter is fear. The dopaminergic mesolimbic pathway has essential role in excitable behavior, and it's role in Parkinson disease. The aim of this research in study, the effect of dopaminergic pathway in fear response.
Methods: The elevated plus maze was used in combination with the percentage of time spent in the open arms of the maze (OAT%) and the percentage of entries into the open arms (OAE%) to measure fear. Increases in the OAT% and OAE% indicate an anxiolytic effect (reduction in anxiety), whereas decreases in the OAE% and OAT% indicate an anxiogenic effect. After five days, the rats were injected with saline and different doses of sulpiride and Bromocriptine.
Results: Results showed that intracerebroventricular administration of sulpiride, in the doses of 5, 20μg/rat and bromocriptine, D2 agonist in doses 65, 95μg/rat produced a significant effect comparing to sham groups (p<0.05). While intracerebroventricular administration of sulpiride 15, 10μg/rat, and bromocriptine 70, 80μg/rat, did not show any significant effect comparing with sham group (p<0.05). In the current research intracerebroventricular administration of sulpiride, D2 antagonist at the doses of 5, 10, 15, 20μg/rat and Bromocriptine, D2 agonist in the doses of 65, 70, 80, 95μg/rat were used and theire effect on the fear behavior were studied.
Conclusions: The possible effect of Dopaminergic system in the fear process, especially D2 receptor increase fear.