The effects made by central serotonergic pathways on blood pressure depend on the subtype of receptors and the brain region examined. In addition, serotonergic modulation of opiatergic func-tion seems to be important in cardiovascular regulation since hypotension induced by selective inhibition of serotonin reuptake is blocked by opioid antagonists in spontaneously (-)-MK 801 hypertensive rats. Furthermore, serotonin is necessary for that maintenance of normal quantities of dynorphin mRNA in many regions of the mind. Taking the above information into account, the goal of the current research was to analyze the possible involvement of brain, and n opioid receptor subtypes in the hypotensive response caused from the activation of central 5 HT3 receptors. Adult male Wistar rats weighing 300 20 g were used in the present research. These were kept under managed light and temperature problems, and had free access to regular water and lab chow. All fresh units were conducted in rats. Groups of mice used in one experimental set weren’t re-used in some other part of the research. Endosymbiotic theory {Five times before experimental sessions helpful information cannula was inserted in to the lateral ventricle under ketamine/xylazine anesthesia. In brief, after placing the rat in a stereotaxic apparatus, a long-term 2-8 gauge guide cannula was implanted according to the subsequent coordinates: anteroposterior 1. 2 mm posterior to the bregma; lateral 1. 5 mm;vertical 4. 0 mmbelow the mind. The guide cannula was fixed to the brain with dental cement and steel screws. After surgery, the animals were housed in individual cages. Two days prior to the fresh periods, a catheter stuffed ALK inhibitor with heparinized saline solution was introduced to the left carotid artery under ketamine/xylazine anesthesia, and exteriorized at the nape of the animals neck to allow blood pressure saving. The place of {the {manual cannula in {LV|cannula in the LV and the intracerebroventricular injection site|the intracerebroventricular injection site|the intracerebroventricular injection site|the intracerebroventricular injection site and the information cannula in LV and the LV was confirmed at the end of the test with the use of Evans Blue dye injected through the cannula. The heads were eliminated, placed in formalin, and later cut and later frozen in to 40 m parts. The slices were analyzed using light microscopy and stained with cresyl violet. Only information from the animals in-which the idea of the cannula was restricted to the cerebroventricular space and the dye could not be viewed in the brain tissue surrounding the ventricle were contained in the research. The following medications were used: m chlorophenylbiguanide hydrochloride biguanide; m CPBG, a selective 5 HT3 agonist was obtained from Tocris Cookson, Inc. Ballwin, MO. Ondansetron, a selective 5 HT3 antagonist, was purchased from Sigma Chemical, Co., St. Louis, MO.