A blood pressure lowering effect of lesions of the caudal periaqueductal gray: relationship to basal pressure.

Basal mean arterial pressure (MAP) measured one week following placement of pontine lesions was markedly lower (-27.85 mm Hg) in cats with bilateral lesions of the caudal periaqueductal gray than in cats with bilateral lesions of the area anteroventral to the locus coeruleus. Regression models of the relationship between basal arterial pressure (MAPbasal) and the change in arterial pressure (MAPchange) after the lesions indicate that lesions of the caudal periaqueductal gray led to a marked decrease in MAP in animals with an elevated basal MAP (MAPchange = MAPbasal x (-1.182) + 139.433; r = -0.902; P less than 0.002). In contrast, lesions of the area anteroventral to the locus coeruleus had no such effect (MAPchange = MAPbasal x (-0.363) + 56.49; r = -0.375; P greater than 0.1). The region of the caudal periaqueductal gray affecting MAP appears anterior to the locus coeruleus and through intrinsic neurons or fibers of passage may play a critical role in control of arterial pressure.