Periaqueductal gray area and cardiovascular function.

The periaqueductal gray (PAG) area seems to play an important role in modulating several biological functions such as the triggering of stereotyped defence and reproductive behaviour, pain, anxiety and cardiovascular and respiratory activities. Anatomically this midbrain area is made up of symmetric neuronal columns arranged along the long axis of the aqueduct. In this paper we review the most important findings of the last 10-15 years about the interaction between the PAG area and the cardiovascular function. It is shown that these neuronal columns within the PAG area exhibit a viscerotropic organization which elicits both hypertensive and hypotensive responses. In particular, the stimulation of the ventral neuronal column evokes a hypotensive response associated with a regional decrease in the vascular resistance. On the contrary, the stimulation of the dorsal and lateral neuronal columns evokes arterial hypertension associated with specific changes of the vascular resistance. Recently the authors demonstrated that the glutamergic system in the PAG area (prevalently through NMDA subtype receptor) may also be involved in the control of cardiovascular system. Moreover, the involvement of the arginine vasopressin neuropeptide in the hypertension induced by administration of excitatory amino acids into the PAG area has been demonstrated.