Possible involvement of CB1 receptors of the ventrolateral periaqueductal gray on cardiovascular responses during hemorrhage in rats

Abstract

The periaqueductal gray (PAG) is a mesencephalic region that surrounds the cerebral aqueduct. The PAG was divided functionally into four longitudinal columns arranged along the rostrocaudal axis: dorsomedial, dorsolateral, lateral and ventrolateral. Microinjection of excitatory amino acids into the ventrolateral PAG (vlPAG) caused decreases in blood pressure, heart rate, sympathetic activity, as well as antinociception, quiescence and hyporeactivity. This syndrome is often associated with pathophysiological conditions such as the loss of large volumes of blood. Experimental studies in mammals have established that hemodynamic responses to blood loss consists of three phases: Phase I compensatory normotensive; Phase II decompensatory; hypotensive and phase III recompensatory post-hemorrhage, when the pressure returns to normal levels.Recent reports have shown that the endocannabinoid system is associated with the pathophysiology of hypotension in various forms of shock, including the hemorrhagic. Interestingly, it has been shown that the hypotension caused by loss of blood was prevented by a pre-systemic treatment with the CB1 antagonist SR141716. Such receptors are densely expressed along the PAG. Therefore, this project has hypothesized that the endocannabinoid system of the vlPAG is involved in the modulation of cardiovascular responses to hemorrhage in rats. (AU)