| A lot of researchers show interest in novelty seeking behavior recently, because of its high connection between high risk taking, compulsive behaviors, for instance, drug abuse, pathological gambling and shopping. Cloninger indicated that basal dopamine level may mediate novelty seeking. Researches showed that higher releasing of dopamine was found in high novelty seekers rather than low ones. And some clinic study found that after receiving dopamine-related medical treatment, low novelty seeking patients tended to be high novelty seekers. However, no exact conclusion was made to explain whether levodopa or other related drugs lead to that change.Levodopa is the precursor to dopamine. Because dopamine cannot enter blood-brain barrier, levodopa is used as a replacement. It is converted by DOPA decarboxylase after entering blood-brain barrier, into dopamine which plays an essential role in the treatment. So administration of levodopa can increase level of dopamine activity in brain. Receptor antagonists, such as dopamine D1receptor antagonists, can decrease dopamine activity by binding dopamine receptors or decreasing sensitivity of dopamine receptors. It means that dopamine activity in brain can be controlled by related drugs.By using Novel Object Discrimination Test whish is a type of widely used Novel Preference Test, this experiment aimed to explore the influence of brain dopamine activity on novelty seeking behavior in healthy rats. In a5×2×3design, Variable1(dopamine activity level in brain) had5levels, including levodopa(100mg/kg), levodopa (50mg/kg),saline, dopamine D1receptor antagonist SCH-23390(0.03mg/kg), SCH-23390(0.1mg/kg); Variable2(novelty of object) had2levels, including novel object, familiar object; Variable3(timeline)had3levels, including0-2min,2-4min,4-6min. And two Dependent Variables would be duration and frequency of contacting of both types of objects. The hypothesis was increasing level of dopamine activity because of administration of levodopa, would enhance novelty seeking in rats, that was increasing both duration and frequency of novel object interaction; and decreasing level of dopamine activity because of SCH-23390injection, would inhibit novelty seeking, that was decreasing both duration and frequency of novel object contacting.40male adult SD rats were involved in the experiment, with8rats/group. And each individual completed the test independently. The whole process was recorded by Canon camera and dependent variables were obtained by Enthovision XT8.0. SPSS16.0was used to analyze the relationship between variables and dependent variables.It indicated by outcomes that the influence of dopamine activity on novelty seeking varied during the exploring time. Comparing to rats with normal dopamine level, hyper dopamine level caused by levodopa injection increased both duration and frequency of novel object interaction during0-2min and2-4min. However, extreme high level of levodopa could in term decrease novelty seeking. Hypo dopamine activity level caused by SCH-23390administration did not affect novelty seeking in either duration or frequency in0-2min, but had a dose-dependent inhibition in duration in2-4min. While the most effective inhibition in frequency was under low dose SCH-23390, rather than high dose in2-4min. In4-6min, only highest level of dopamine activity could keep novelty seeking, while other groups don’t.In conclusion, in0-2min and2-4min, dopamine activity level had a inverted-U effect on duration of novelty seeking, and a U effect on frequency of novelty seeking. |
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