Deterministic nature of baroreceptor firing

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Abstract
Single-fiber baroreceptor firing was recorded from the common carotid nerve and a branch of the aortic nerve of anesthetized cats. The responses to a variety of repetitive input pressure waveforms were examined in order to determine to what extent random variations within the impulse-generating mechanism of the receptors influence the times at which nerve firings occur. The nerve firing times were highly reproducible when the pressure cycle contained a sharp pressure increase, and the baroreceptor had not been firing prior to the pressure rise. Natural pressure waveforms at normal pressure levels fulfilled these conditions. At constant pressure levels, fluctuation in the time interval between successive nerve firings was found to increase with the mean interval. A significant part of the variability in baroreceptor firing times could be attributed to slight fluctuations in the perfusion pressure. The results indicate that descriptions of single-fiber baroreceptor activity in terms of instantaneous firing frequency give an inadequate characterization of the neural firing.