Synaptic behaviour of myenteric neurones in the gastric corpus of the guinea-pig.

1. Synaptic behaviour of ganglion cells in the myenteric plexus of the corpus of the guinea-pig stomach was investigated using intracellular recording methods. Synaptic potentials were evoked by focal electrical stimulation of interganglionic fibre tracts or the surface of the ganglion containing the cell body from which the recording was obtained. 2. Fast excitatory postsynaptic potentials (EPSPs) mediated by nicotinic cholinergic receptors were the most common stimulus-evoked or spontaneously occurring synaptic events. 3. Fast EPSPs were evoked in every neurone and most neurones received multiple inputs from axons arriving in several different interganglionic fibre tracts. Several neurones received input from multiple axons in individual fibre tracts. 4. Fast EPSPs were evoked at stimulus frequencies up to 80 Hz without evidence of the 'run-down' phenomenon that characterizes fast EPSPs in the intestine. 5. Trains of EPSPs in the ganglion cell soma occurred with relatively long latencies following spike discharge evoked by intracellular current injection in the same neurone. This appeared to reflect return of excitatory synaptic input to the soma along recurrent connections within the synaptic network. 6. The safety factor for fast EPSPs to evoke spike discharge was highest for gastric I neurones. Probability of fast EPSPs triggering spikes was intermediate in neurones classified electrophysiologically as gastric II and was lowest in gastric III neurones, which never discharged spikes during a fast EPSP. 7. No slow excitatory or inhibitory synaptic potentials, like those found in intestinal ganglion cells, were evoked in gastric neurones by focal stimulation of the fibre tracts. 8. The results suggest that myenteric neurones in the gastric corpus of the guinea-pig have distinctive synaptic behaviour different from intestinal neurones in the same animal. This may be a reflection of adaptation for neural control of the specialized function of the effector systems in this region of the stomach.