Electrophysiological and morphological properties of type C vagal neurons in the nodose ganglion of the cat.

Some passive and active electrical properties of type C neurons were studied intracellularly, in situ, in the nodose ganglia of adult cats. From the neuronal responses to hyperpolarizing and depolarizing rectangular current pulses it was possible to determine the input resistance (34.4 M omega) and specific membrane resistance (2373 omega.cm2). Significant changes in magnitude and duration of the action potential evoked by vagal stimulation result from changes in the resting potential caused by the passage of steady polarizing currents across the cell membrane. The action potentials evoked by infranodose vagal stimulation had a long duration, a long latency and comprised several components. The fast main spike was followed by a long post-hyperpolarization. The double shock technique showed that the fast main potential was composed of an initial segment spike ('A spike') and a somatic spike ('S spike'), and made it possible to determine the somatic refractory periods. After electrical identification of the cells, horseradish peroxidase was injected ionophoretically into the soma, and it was shown that the central processes were about four times smaller in diameter than the peripheral processes.