Two Kinds of Parasympathetic Post-Ganglionic Motor Neurons in the Dog Urinary Bladder

In separated preparations of smooth muscle layers, the electrical stimulations with 0.5 msec pulses have been utilized to reveal the nature of motor neurons in the dog urinary bladder. In the outer longitudinal muscle layer, contraction elicited by pulses was depressed after exposure to atropine (5×10-7 g/ml). In the middle circular muscle layer, however, atropine caused no diminution of contraction due to pulses, despite massive atropinization (5×10-6 g/ml). Contraction due to pulses was abolished by tetrodotoxin, but was not reduced by hexamethonium in both muscle layers. These results imply that there exist two kinds of parasympathetic motor neurons in the dog urinary bladder; atropine-sensitive neurons in the outer longitudinal muscle layer and atropine-resistant neurons in the middle circular muscle layer.