Tonic sympathetic excitation and vasomotor control from pontine reticular neurons

The pontine reticular formation (PRF) was explored for regions providing tonic control of arterial pressure, heart rate, and activity of sympathetic nerves. In Saffan (alfaxalone-alfadolone)-anesthetized rats, discharge of neurons in the PRF or rostral ventrolateral medulla (RVLM) was inhibited by microinjections of glycine (1 M; 65 +/- 2 nl). PRF blockade caused large, short-lasting (116 +/- 17 s) decreases in arterial pressure and equal decreases in renal (-47 +/- 4%) and splenic (-45 +/- 4%) nerve activity, indicating that PRF neurons contribute to resting control of vasomotor discharge. In contrast, RVLM blockade caused long-lasting (41 +/- 3 min) decreases in arterial pressure and unequal decreases in activity of renal (-50 +/- 4%) and splenic (-31 +/- 6%) nerves. The short duration of the responses to PRF blockade could not be attributed to compensation by baroreceptors or by actions specific to glycine. Excitation of PRF neurons with amino acids caused increases as well as decreases in arterial pressure and sympathetic activity, and therefore activated neurons distinct from those that are tonically active. These results identify a source of cardiovascular control in the reticular formation of the pons that provides tonic excitatory drive to sympathetic nerves and that differs from the well-known source in the RVLM.