Tonic control of arterial pressure and regional hemodynamics by supra-medullary sites.

We examined the role of pontine sites in the tonic control of vasomotor tone under normal and reduced tidal volumes. Lidocaine was microinjected in pons at the level of the Kölliker-Fuse nucleus (KFN). Injections were made bilaterally 6, 7, 8, and 9 mm below dura, and 0.9 and 2.5 mm lateral to midline. Lidocaine in KFN produced a fall (-14 mmHg) in mean arterial pressure (MAP) at normal and reduced tidal volumes. These effects were mediated primarily by a reduction in hindquarter vascular resistance. Lidocaine into a ventromedial site (8.0 mm beneath dura, 0.9 mm lateral to midline) increased MAP by increasing renal, mesenteric, and hindquarter vascular resistance. After sino-aortic deafferentation (SAD), reduced tidal volume augmented the pressor and blunted the tachycardic responses to lidocaine injected into the ventromedial pons (9.0 mm beneath dura, 0.9 mm lateral to midline). SAD also enhanced the pressor response to lidocaine injected into ventromedial pons. This work demonstrates a role for supra-medullary sites in the tonic control of vasomotor tone.