Membrane responses of neurons in human sympathetic ganglia

Electrophysiological studies were performed on in vitro slice preparations of sympathetic ganglia excised from peripherally perfused, brain-dead human donors. The intracellular recordings in 16 neurons showed resting potentials and input resistances mostly in the ranges reported for sympathetic neurons in other mammals. The high input resistances (approximately 29 M omega) can account for the long membrane time constants measured in three neurons (means = 13.9 ms). Spikes that were part of anodal break responses as well as those evoked by current pulse injections were tetrodotoxin sensitive and were more prolonged in duration by tetraethylammonium than by 4-aminopyridine applications. Administrations of isoflurane (0.5-2 minimum alveolar concentrations) by perfusion did not greatly affect the membrane properties, but produced a marked reduction in repetitive spike firing evoked by current pulse injections as well as in the postspike afterhyperpolarizations, suggesting that a sympathetic neurogenic mechanism may contribute to the hypotension observed clinically during isoflurane anaesthesia. These investigations demonstrate for the first time that human sympathetic ganglion neurons can be studied successfully in in vitro preparations, and hence are valuable for direct relevance to the human condition.