Intracellular recordings from ganglia of the thoracic sympathetic chain of the guinea-pig.

1. Intracellular recordings have been obtained from cells of thoracic paravertebral sympathetic ganglia of guinea-pigs.2. Resting potentials were 50-70 mV. The steady-state current-voltage curve was linear for all hyperpolarizations and usually for depolarizations up to 10 mV. The slope of this curve was 19-186 MOmega (mean 55 MOmega). Time constants of cells were 6-14 msec (mean 9.1 msec).3. Most cells maintained a high rate of firing of action potentials during strong current pulses.4. Indirect stimulation via the rami communicantes or the interganglionic nerves of the sympathetic chain evoked a graded synaptic response which could lead to the discharge of one or more action potentials. Hexamethonium blocked the responses to such stimulation. Occasionally an all-or-none response remained, apparently conducted antidromically along the cell's axon.5. Spontaneous synaptic potentials were observed. Their occurrence frequency was increased during indirect stimulation. If they are assumed to represent single quanta of release of transmitter, the quantal content of a threshold synaptic potential was 8-20 quanta.6. Preganglionic fibres could ascend at least three segments or descend two after entering the sympathetic chain. They had conduction velocities of 0.1-1.1 m/sec.7. Inexcitable cells were frequently impaled. Repetitive indirect stimulation gave rise in these cells to a large (20 mV) slow depolarizing response.