Neuronal activity recorded extracellularly from in situ canine mediastinal ganglia

Spontaneous activity of 226 neurons was recorded from in situ mediastinal ganglia in 10 dogs. Forty-two percent of these were active during specific phases of the cardiac cycle, primarily during systole. Cardiovascular-related activity occurred when systolic pressure was between approximately 70 and 185 mmHg (1 mmHg = 133.3 Pa) whether the pressure was altered by positive inotropic pharmacological agents or cross clamping of the aorta. Twenty percent of the identified neurons displayed respiratory-related activity which occurred during positive pressure inflation or deflation. Thirty-eight percent of the identified neurons displayed bursts of activity or sporadic activity. The activity of 17% of the identified neurons was altered by gentle mechanical distortion of localized regions of the neck, left elbow, ventral thoracic wall, ventral abdominal wall, superior vena cava, right ventricle, or aorta. In the majority of instances cardiovascular- or respiratory-related activity persisted following acute decentralization, indicating that neurons in mediastinal ganglia can function in the absence of influences of central nervous system neurons. Five percent of the identified neurons were activated by single 1-4 ms, 10-20 V stimuli delivered at 0.5 Hz to the nerves connected with either the cranial or the caudal poles of the mediastinal ganglion or the ansae. These neurons were activated after a fixed latency when 0.5 Hz was used and in most instances when 10 Hz was used. These data indicate that 5% or less of the neurons identified projected axons out of the mediastinal ganglia investigated.(ABSTRACT TRUNCATED AT 250 WORDS)