Synaptic transmission in the decentralized middle cervical ganglion of the dog

The middle cervical ganglion (MCG) was decentralized in 30 dogs by cutting the thoracic vagus and rami on one side. Two or more cardiopulmonary nerves were then dissected free and placed on bipolar stimulating and recording electrodes in mineral-oil baths. Stimulation of one cardiopulmonary nerve generated a compound action potential (CAP) in one or two others. The CAP was altered by changing the frequency of stimulation and by stimulating preganglionic fibers in the rami. These alterations displayed latency changes and temporal summation or inhibition. The ansae were sectioned to neurally isolate the MCG from the stellate ganglion. A CAP generated after blockade by hexamethonium, atropine, propranolol and phentolamine was abolished transiently by chymotrypsin, and for longer periods by manganese, injected locally into the MCG. These results suggest that a CAP that is generated by stimulating one cardiopulmonary nerve in a decentralized MCG and recorded from another may result from synaptic activity in the MCG and that complex neuronal interactions occur within the MCG.