ACTIVITIES OF OREXIN NEURONS IN MOTIVATIVE BEHAVIOR

Abstract Background Orexin neurons regulate physiological functions, including not only energy homeostasis and wakefulness, but also motivated behaviors. Aims & Objectives Here, we examined the roles of orexin neurons in motivated behaviors. [Method] We measured the activities of orexin neurons using fiber photometry under a free-moving condition, in which the rats were subjected to the fixed ratio (FR) or progressive ratio (PR) schedule of a touchscreen-based automated operant task. Results We found that breakpoint in PR test was increased when orexin neurons were activated by using chemogenetic approach, while the breakpoint was reduced when orexin neurons were disrupted by diphtheria toxin A. We also found that under FR5 conditions in which rats were able to obtain a food pellet by touching the screen consecutively five times, the activity in orexin neurons was increased after the fifth screen touch (after which one food pellet is delivered). The activity peaked before rats obtained reward, and then decreased after food intake. Next, we measured orexin neurons activities under FR20 which seems to be more difficult for rats to obtain rewards, compared with those under FR5. Under FR20 conditions, the orexin activities were higher than those in FR5 conditions. In the PR schedule test, the orexin activities were also gradually increased. Discussion & Conclusion These observations suggest that the orexin activities are associated with motivational behaviors, and that dynamic changes in activation of orexin neurons may be involved in craving and reward prediction, and satisfaction.