Tachykinins mediate slow excitatory postsynaptic transmission in guinea pig sphincter of Oddi ganglia

Intracellular recording techniques were used to test whether tachykinins co uld be mediators of slow excitatory postsynaptic potentials (EPSPs) in guin ea pig sphincter of Oddi (SO) ganglia. Application of the tachykinin substa nce P (SP) onto SO neurons caused a prolonged membrane depolarization that was reminiscent of the slow EPSP in these cells. Pressure ejection of the n eurokinin 3 (NK3) receptor-specific agonist senktide caused a similar depol arization; however, no responses were detected on application of NK1 or NK2 receptor agonists. The NK3 receptor antagonist SR-142801 (100 nM) signific antly inhibited both SP-induced depolarization and the stimulation-evoked s low EPSP, as did NK3 receptor desensitization with senktide. Capsaicin, whi ch causes the release of SP from small-diameter afferent fibers, induced a depolarization that was similar to the evoked slow EPSP in both amplitude a nd duration. The capsaicin-induced depolarization was significantly attenua ted in the presence of SR-142801. These data indicate that tachykinins, rel eased from extrinsic afferent fibers, act via NK3 receptors to provide slow excitatory synaptic input to SO neurons.