Role of Acetylcholine Microinjection into the Ventral Tegmental Area on the Cardiovascular Response in Anesthetized Rats

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 ۵۰ male Wistar rats (۲۵۰–۳۰۰ g). Acetylcholine was microinjected into the VTA in volumes of ۱۰۰ 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 ۵, ۱۰, ۲۰ and ۴۰ nmol/۱۰۰ nl) caused a dose related decrease in mean arterial pressure. The best physiological response was elicited by Ach ۲۰ nmol/۱۰۰ nl that decreased both mean arterial pressure and heart rate (MAP:-۳۰.۶۱ mmHg and HR:-۱۴beats/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.

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Keywords: Ventral tegmental area , Acetylcholine , Blood pressure , Heart rate