PONTINE RETICULAR NEURONS PROVIDE TONIC EXCITATION TO NEURONS IN ROSTRAL VENTROLATERAL MEDULLA IN RATS

To determine whether the pontine reticular formation (PRF) is a source of tonic activity for cardiovascular neurons in the rostral ventrolat eral medulla (RVLM), the discharge of PRF neurons was inhibited by uni lateral microinjections of glycine (1.0 M; 60 nl) while recording the discharge of single neurons in the RVLM in 14 Saffan-anesthetized rats . RVLM units were characterized as cardiovascular if their spontaneous activity was changed by baroreceptor activation and was synchronized to the cardiac cycle. Glycine injection into the ipsilateral PRF elimi nated the ongoing activity of six cardiovascular units and reduced the activity of four (mean decrease -91 +/- 4%). Inhibition of these unit s lasted 20-115 s (mean 59 +/- 9 s). Glycine injection into the PRF ha d no effect on the discharge of five cardiovascular units. Activity of six noncardiovascular units did not respond to PRF blockade. Glycine injection into the PRF caused decreases in arterial pressure (-28 +/- 5 mmHg), heart rate (-23 +/- 3 beats/min), and renal nerve activity (- 42 +/- 7%) that also returned to control values between 25 and 120 s ( mean 55 +/- 5 s). These results indicate that PRF neurons provide toni c excitatory drive to some cardiovascular neurons located in the RVLM.