FIGURE 7.

Very-low-frequency oscillations of upper thoracic preganglionic sympathetic neurons and arterial pressure in a Nembutal-anesthetized cat. (A) Recordings of an intermediolateral cell column preganglionic sympathetic neuron conducted contemporaneously with the acquisition of dynamic arterial pressure magnitude. Unitary recordings of the preganglionic sympathetic neuron reveal regular fluctuations oscillating with a frequency corresponding with vasogenic autorhythmicity. Time constant integration of unitary discharge of action potentials expressed as frequency readily evidences regularly rhythmic oscillatory pattern of the discharge. The oscillations are synchronized, though out-of-phase, with the arterial pressure waveform recording. Peaks of preganglionic sympathetic neuronal firing frequency precede peaks of dynamic arterial pressure magnitude by a time delay corresponding with the delay of neurosynaptic transmission across the vascular neuroeffector junction and propagation of changes of net arteriolar tone throughout the vascular tree. (B) Pharmacological antagonism of a adrenergic receptors utilizing phentolamine effectively eliminates oscillations from dynamic arterial pressure magnitude, though these waves persist in preganglionic sympathetic neuronal discharge, exhibiting a central frequency approximating that of vasogenic autorhythmicity. Thus, interfering with vascular neuroeffector electrochemical transduction prevents very low frequency oscillations from becoming manifest in hemodynamic variabilities peripherally. Modified with permission from Preiss and Polosa (1974).