Character of the excitatory neurotransmission in dog terminal ileum

In vitro experiments were performed on smooth muscle strips cut out longitudinally or circularly from the terminal ileum at about 5 cm from sphincter ileo-colocum of 3-4-month old and adult dogs. Studies were made on the postsynaptic responses of single smooth-muscle cells to transmural electrical stimulation of strips placed in sucrose gap, as well as on the contraction changes in response to field electrical stimulation of strips placed in organ bath. Field electrical stimulation elicited mainly excitatory responses of the muscle strips. Using cholino- and adrenoreceptor-antagonists and serotonergic receptor-blockers, we found that the majority of responses were cholinergic and a small part of them were alpha-adrenergic. Excitatory serotonergic responses were also obtained. The nerve nature of the responses was proved by tetrodotoxin. Single smooth-muscle cells gave predominantly excitatory postsynaptic responses to transmural stimulation of the smooth muscle strips. The pattern of both postsynaptic and contractile responses changed in the presence of the antagonists used. The present results suggest the predominance of cholinergic transmission in the contractile responses of the terminal ileum.