Electrical behaviour of myenteric neurones in the gastric antrum of the guinea-pig.

1. Intracellular microelectrodes were used to study the electrical behaviour of ganglion cells in the myenteric plexus of the antrum of the guinea-pig stomach. In the absence of any information on antral myenteric neurones, the aim was to characterize the electrical behaviour and identify biophysical properties of the neurones that could be related to specialized organization of the neural microcircuits in this physiologically important division of the stomach. 2. Myenteric neurones in the gastric antrum were classified into four subtypes based on electrophysiological properties. These were gastric I, II, III and AH/type 2 neurones. Gastric I neurones were characterized by repetitive spike discharge during intraneuronal injection of depolarizing current, by higher input resistances and by lower resting membrane potentials than the other cell types. Gastric II neurones did not discharge repetitively. They discharged one or two spikes only at the beginning of depolarizing current pulses. Gastric III neurones did not discharge action potentials in response to depolarizing pulses. These neurones had higher membrane potentials and lower input resistances than the other types. A fourth type of neurone discharged one or more spikes during depolarizing current pulses and had long-lasting hyperpolarizing after-potentials associated with the spikes. The behaviour of these neurones was like AH/type 2 neurones found elsewhere in the enteric nervous system. 3. Action potentials in gastric I and II neurones were abolished by tetrodotoxin. Spikes of the AH/type 2 cells were not abolished by tetrodotoxin due to a calcium component of the inward current. Application of tetraethylammonium broadened the spikes. This was reversed by removal of Ca2+ from the bathing medium. 4. The hyperpolarizing after-potentials of AH/type 2 neurones were suppressed by removal of Ca2+ from the bathing medium. Treatment with 4-aminopyridine decreased the amplitude and duration of the after-hyperpolarization, whereas tetraethylammonium increased the duration and amplitude of the after-potentials. The hyperpolarizing after-potentials were unaffected by apamin. 5. Elevation of cyclic 3',5'-adenosine monophosphate by forskolin resulted in excitation of all AH/type 2 neurones and some of the gastric III cells. Gastric I and II neurones were unaffected. 6. The electrophysiological behaviour of myenteric neurones in the antrum was similar in some respects and different in others from neurones in the gastric corpus and the small and large intestine of the same animal. The differences may reflect distinct organization of the microcircuits for the specialized neural control of the effector functions which characterize the gastric antrum.