Membrane and action potential characteristics of A and C nodose ganglion cells studied in whole ganglia and in tissue slices.

Abstract

Nodose ganglia and lengths of central and peripheral vagus were excised from anesthetized cats. Ganglia were placed in flowing mammalian saline (at 37.degree. C) and the nerves immersed in mineral oil for stimulation and recording. Ganglion somata were impaled with microelectrodes for recording of resting membrane (MP) and action (AP) potentials. This method identified neurons associated with myelinated fibers (A-cells) and those with unmyelinated axons (C-cells). Current was passed through the electrode for measuring time constant (.tau.), input resistance (Ro) and capacitance (Co), and for directly eliciting AP. A- and C-cells had similar MP and Ro. Other cells had large MP, but AP were not elicited with strong depolarizing pulses. These cells depolarized slowly during repetitive vagal stimulation and were hyperpolarized by injection of repetitive positive-current pulses. In other experiments the ganglion was sliced and sections of 100-150 .mu.m were placed in flowing saline at 36.degree. C. A computerized method, using a discriminant function, was used to distinguish between A- and C-cells. These experiments revealed that A- and C-neurons have similar diameters and that the cells survive well in the slices. Some of the recorded parameters such as MP, .tau., AP afterhyperpolarization (AHP) amplitudes, time-dependent rectification, and capacity to give multiple spikes to long depolarizing pulses were identical to those obtained in intact ganglia. Other values such as Ro of C-cells were higher, and CO of the same cells were smaller in slices. Visualization of the neurons allowed measurements of the specific resistance (Rm) and capacitance (Cm). A- and C-cells had similar Rm, but A-neurons showed a smaller Cm. Ionic substitution experiments revealed that the AP of both types of neurons had a Na, and, possibly, a Ca component.