Contribution of the periaqueductal grey matter to the development of hypertension in the spontaneously hypertensive rat.

The dorsomedial periaqueductal grey matter (PAG) of the mid-brain, an important area for organizing the 'defence reaction', was destroyed using radiofrequency lesions in young, pre-hypertensive spontaneously hypertensive rats (SHRs). During the 12 weeks after surgery, systolic blood pressure (SBP) measured by an indirect tail-cuff technique was consistently lower than that of a sham-operated control group of SHRs (final readings of SBP: sham group (n = 6): 239.1 +/- 4.7 mmHg; lesion group (n = 8): 211.1 +/- 8.2 mmHg; P less than 0.05). Subsequent direct measurement of blood pressure in these rats by cannulation of the ventral tail artery indicated that the SBP in both groups was nearly the same (sham group: 204.7 +/- 5.1 mmHg; lesion group: 203.5 +/- 5.1), lying close to the value obtained by the tail-cuff method in the lesion group. Therefore, lesions of the PAG merely prevented the elevation of blood pressure in the SHR caused by the heating and restraint required for indirect measurement of SBP. Furthermore, ablation of the dorsal PAG had no effect on levels of circulating catecholamines, and did not prevent the cardiovascular response to an alerting stimulus (vibration). It is concluded that this region of the brain is not responsible for the development of hypertension in the SHR.