Descending projections from the ventrolateral medulla and cardiovascular control.

Antidromic responses were evoked in neurones in nucleus paragigantocellularis lateralis (PGL) by stimulation of the ipsilateral ventrolateral white matter or the contralateral dorsolateral white matter at T13-L1 in the cat. Estimated conduction velocities in the spinally projecting axons ranged from 5.0-61 m/s. Stimulation of cell bodies in PGL, by microinjection of D,L-homocysteic acid, usually produced a rise in blood pressure accompanied by tachycardia or bradycardia and either dilatation or constriction in the hindlimb muscle vasculature. It is suggested from this other and evidence that tonically active neurones in PGL may play a role in setting the resting level of blood pressure but that the output of these and other cells in the nucleus may also be modified to generate different patterns of cardiovascular adjustment.