Effects Of Oxytocin And Its Combination With SCH 23390 On Urgent Decision In Rats

Impulsive behavior refers to actions that are poorly conceived, prematurely expressed, unduly risky, or inappropriate to the situation and that often result in undesirable outcomes. Impulsive choice which belongs to impulsive behavior is generally defined as the preference for small immediate or large risky reward versus large delayed or small likely one.Several studies using the delay-discounting paradigm have demonstrated the contributions of cholinergic system and dopaminergic system to impulsive choice. In addition, research results would display pronounced differences in rats differed in basal level of impulsivity (BLI). So far, more researches were focused on the neurobiological mechanisms underlying the effect of dopamine on impulsive choice, but few talked about how acetylcholine played a role in impulsive choice. Besides, there was the evidence of cholinergic-dopaminergic interactions in certain brain regions related to impulsive choice, especially medial prefrontal cortex. From all above, the aim of the present study was to investigate whether dopaminergic system mediated changes in impulsive choice induced by muscarinic cholinergic drug and whether the effect was dependent on BLI.In the present study, sixteen Sprague-Dawley rats were trained on the delay-discounting task. The whole procedure could be attributed to two periods, that is, training and testing period. The purpose of the first experiment was to develop the delay-discounting model among rats with different profiles of impulsive choice. The second experiment was designed to examine whether high BLI rats and low BLI rats would exhibit differences in responses to muscarinic cholinergic agonist oxotremorine (0.025,0.05and0.075mg/kg). In the third experiment, the effects of acute administration of D,-like antagonist SCH23390(0.005,0.0075and0.01mg/kg) after oxotremorine (0.05mg/kg) on impulsive choice were assessed in two sub-populations of rats.The results revealed that pronounced difference was existed in choice of the large delayed reward between high BLI rats (n=8) and low BLI rats (n=8) in the first experiment. During the next experiment, acute oxotremorine administration (0.05and0.075mg/kg) significantly increased choice of the large delayed reward in high BLI rats and significantly decreased choice in low BLI rats. However, oxotremorine (0.075mg/kg) significantly increased all rats’average latency to make response and the percentage of response omissions in total trails. In the last experiment, SCH23390(0.005,0.0075and0.01mg/kg) significantly inhibited the dramatic increase of choice of the large delayed reward induced by oxotrmorine (0.05mg/kg) in high BLI rats, and SCH23390(0.0075mg/kg) significantly enhanced the dramatic decrease of choice in low BLI rats. Nevertheless, acute SCH23390administration (0.01mg/kg) after oxotremorine (0.05mg/kg) significantly decreased all rats’ choice of the large delayed reward when0s delay was applied to this reward, and significantly increased all rats’average latency to make response as well as high BLI rats’ percentage of response omissions in total trails.The results therefore show that oxotremorine decreases impulsive choice in high BLI rats and increases impulsive choice in low BLI rats. What is more, SCH23390inhibits oxotrmorine-induced decrease of impulsive choice in high BLI rats, and enhances oxotrmorine-induced increase of impulsive choice in low BLI rats. The findings further suggest that dopaminergic system might mediate changes in impulsive choice induced by muscarinic cholinergic drug.