Electrical impedance and vasomotor changes accompanying synaptic transmission in sympathetic ganglia

Abstract

Electrical impedance changes within the superior cervical sympathetic ganglion of the cat were recorded at 17.5 kc under various conditions at rest and during synaptic activity. Local blood flow changes in the ganglion were also assessed from the pulsatile component of the impedance bridge output. The following impedance baseline changes were obtained with the ganglion at rest: a decrease after electrode insertion and hypoventilation, and an increase with hyperventilation, asphyxia, and barbiturate anesthesia. Synaptic activity typically gave rise to an initial drop in impedance followed by a prolonged rise. The falling phase of impedance, resistant to hypoxia, fatigue, and hexamethonium, has been tentatively related to presynaptic events, and the rising phase, from similar evidence, to postsynaptic activity. All observed impedance changes were interpreted in terms of changes in relative size of the extracellular fluid compartment. Although small and short-lasting increases in blood flow with synaptic transmission were observed, blood flow changes were not found to be a necessary accompaniment of synaptic activity.