AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 4 680-R689, Copyright © 1986 by American Physiological Society
Cardiac input to medullary reticular formation: neuronal responses to mechanical stimuli
R. W. Blair
Neurons in the medullary reticular formation were tested for responses to
mechanical stimuli applied to the heart in cats anesthetized with
chloralose and paralyzed with pancuronium. In most experiments
baroreceptors were denervated. Aortic occlusion excited 15 neurons (19%)
and decreased the mean discharge rates of five neurons (6%). Discrete
probing of the heart elicited one to three spikes from 18 of 27 neurons
tested. Thirteen of these cells had defined cardiac receptive fields;
fields were large, often encompassing most of the left ventricle. Of 12
neurons tested for responses during fibrillation, 8 were excited, 2 were
inhibited, and 2 were unaffected. Neurons often exhibited different
sensitivities to these mechanical stimuli, as well as to ischemia produced
during coronary arterial occlusion. Neurons were more likely to respond to
stimuli that affected a large mass of myocardium. In addition to cardiac
input, 98% of neurons in this study also received input from at least one
additional sensory modality, and 39 cells were excited by somatic,
auditory, and visual stimuli. Results indicate that medullary reticular
neurons are responsive to mechanical events in the heart as well as to
myocardial ischemia and respond to other sensory modalities.
