Background and Objective: Food deprivation increases the expression of orexin-1 receptor gene in the hypothalamus. On the other hand, food deprivation induces analgesia and orexin has a fundamental and well known role in pain modulation. This study aimed to determine the role of orexin receptor 1 antagonist in analgesic effect of acute food deprivation (12 h) by hot plate test in male rats.

Materials and Methods: Male Wistar rats were divided into 5 groups (n=8), control, food deprivation without surgery, stereotaxic surgery with vehicle, vehicle and food deprivation and food deprivation and orexin receptor 1 antagonist groups. 12 hours before the hot plate test, food was removed from the animals’ proximity, but water was freely available. All groups were tested using the hot plate. Data were analyzed statistically by one-way ANOVA with Tukey post hoc test.

Results: According to our findings, orexin receptor 1 antagonist injection increased pain related behaviors at the time of 5(P<0.05), 15(P<0.05), 30(P<0.01) and 60(P<0.001) minutes in the hot plate test.

Conclusion: Orexin plays an important role in feeding state–induced pain modulation. Based on our results, change in pain behavior induced by food deprivation may be related to change in orexin expression or in orexin receptors density.

Background and Objective: The Ventral Tegmental Area is a part of the mesolimbic structure. In addition to its role in motivation, mood, cognition, schizophrenia, addiction and Parkinson’s disease, it is involved in the regulation of the cardiovascular system. The presence of cholinergic afferent fibers in the VTA has been demonstrated but there is no specific information about its role in cardiovascular regulation. This study was performed to determine the possible role of the cholinergic system on mean arterial blood pressure (MAP) and heart rate (HR) by microinjection of different doses of acetylcholine into the VTA of urethane anesthetized rats.

Materials and Methods: Experiments were performed on 50 male Wistar rats (250–300 g). Acetylcholine was microinjected into the VTA in volumes of 100 nl using a stereotaxic system. Blood pressure and heart rate were recorded before and throughout each experiment by power lab system. The average changes in the mean arterial pressure and heart rate at different intervals, were compared using paired t-test and one-way ANOVA.

Results: Acetylcholine microinjections in VTA (Ach 5, 10, 20 and 40 nmol/100 nl) caused a dose related decrease in mean arterial pressure. The best physiological response was elicited by Ach 20 nmol/100 nl that decreased both mean arterial pressure and heart rate (MAP:-30.61 mmHg and HR:-14beats/min). Microinjection of the same volume of saline produced no significant changes in either MAP or HR.

Conclusion: We showed for the first time that, microinjection of acetylcholine into the VTA evokes a depressive cardiovascular response.