Neuroscience
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Forced choice between alternative options of unpredictable outcome is a complex task that requires continual update of the value associated with each option. Prefrontal areas such as the orbitofrontal cortex (OFC) have been shown to play a major role in performance on ambiguous decision-making tasks with substantial risk component, broadly named as "gambling tasks." We have recently demonstrated that rats display complex decision-making behavior in a rodent gambling task based on serial choices between rewards of different value and probability. This rodent task retains many of the key characteristics of the human Iowa Gambling Task (IGT), and performance in this novel task is also disrupted by OFC or amygdalar lesioning. ⋯ We found that animals with a monoarthritic inflammatory model of chronic pain systematically preferred the lever associated with larger but infrequent rewards. In addition, we measured the neurochemical content of the OFC, amygdala and nucleus accumbens using HPLC, and found that in prolonged chronic pain animals there was a decrease in the tonic levels of dopamine, DOPAC (3,4-hydroxyphenyl-acetic acid) and 5-HIAA (5-hydroxyindole-3-acetic acid) in the OFC. This is the first report of the effect of chronic pain in rat decision-making processes and supports the notion that pain may have profound effects on the functioning of the reward-aversion circuitry relevant to strategic planning.
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It has been long known that the physiological concentrations of polyamines putrescine, spermidine and spermine are essential for cell growth. However, the role of endogenous polyamines in behavior function is poorly understood at present. This study investigated animals' behavioral performance and neurochemical changes in the hippocampus and prefrontal cortex following i.c.v. microinfusion of difluoromethylornithine (DFMO), a potent inhibitor of putrescine synthesis. ⋯ These results demonstrate that acute depletion of putrescine by DFMO produces anxiety-like behavior and impairs memory for the object displacement without affecting animals' locomotor and exploratory activity and spatial learning and memory. Multiple regression analysis data suggest the different roles of endogenous putrescine, spermidine and spermine on behavior function. The spermidine/spermine and glutamate/GABA ratios in hippocampal DG are strongly associated with anxiety-like behavior in the DFMO rats.