Activity patterns of cardiac vagal motoneurons in rat nucleus ambiguus.
Extracellular recordings were made in the right nucleus ambiguus of urethane-anesthetized rats from 33 neurons that were activated at constant latency from the craniovagal cardiac branch. Their calculated conduction velocities were in the B-fiber range (1.6-13.8 m/s, median 4.2), and most (22/33) were silent. Active units were confirmed as cardiac vagal motoneurons (CVM) by the collision test for antidromic activation and by the presence of cardiac rhythmicity in their resting discharge (9/9). Brief arterial pressure rises of 20-50 mmHg increased the activity in five of five CVM by 0.1 +/- 0.02 spikes. s(-1). mmHg(-1) from a resting 3.8 +/- 1.2 spikes/s; they also recruited activity in two of four previously silent cardiac branch-projecting neurons. CVM firing was modulated by the central respiratory cycle, showing peak activity during inspiration (8/8). Rat CVM thus show firing properties similar to those in other species, but their respiratory pattern is distinct. These findings are discussed in relation to mechanisms of respiratory sinus arrhythmia.
Rentero
N
N
Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3010, Australia.
Cividjian
A
A
Trevaks
D
D
Pequignot
J M
JM
Quintin
L
L
McAllen
R M
RM
D000200:Action Potentials; D000818:Animals; D017704:Baroreflex / Q000502:physiology; D001479:Basal Ganglia / Q000166:cytology* / Q000502:physiology*; D006321:Heart / Q000294:innervation*; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012119:Respiration; D014630:Vagus Nerve / Q000166:cytology* / Q000502:physiology*