Role of the glutamatergic system of ventrolateral periaqueductal gray (vlPAG) in the cardiovascular responses in normal and hemorrhagic conditions in rats

Abstract

Objective(s): Periaqueductal gray (PAG) is a mesencephalic area divided into four columns including ventrolateral periaqueductal gray (vlPAG). vlPAG plays a role in cardiovascular regulation during normal and hemorrhagic (Hem) conditions. Due to presence of glutamate in this area, we evaluated the effect of glutamatergic receptors of this area on cardiovascular activity in normotensive and hypovolemic Hem rats.Materials and Methods: Animals were divided into twelve groups: saline (vehicle), Glutamate, GYK52466 (non-NMDA receptor antagonist), and MK801 (NMDA receptor antagonist) with and without Glu microinjected into vlPAG in normal and Hem conditions. Following the femoral artery cannulating and microinjecting, changes (Δ) of heart rate (HR), systolic blood pressure (SBP), and mean arterial pressure (MAP) were recorded via a PowerLab unit.Results: In normotensive conditions, microinjection of Glu increased ΔMAP, ΔSBP, and ΔHR (p 0.05) but co-injection of MK-801 with Glu significantly attenuate these effects(p 0.05).Conclusion: The glutamatergic system of vlPAG increases cardiovascular values that are mostly mediated through the NMDA receptor. Since vlPAG is well known as an inhibitory region, it seems that glutamate does not have a noteworthy cardiovascular role in vlPAG during Hem and normal conditions.

Keywords

• cardiovascular system
• periaqueductal gray
• hemorrhage
• glutamic acid
• blood pressure