Sympathetic input to ganglia of the guinea pig sphincter of Oddi.
Intracellular recording and immunohistochemical staining techniques were used to establish whether sphincter of Oddi (SO) ganglia are a target of sympathetic input to this region. Norepinephrine (0.01-10.0 microM) decreased the amplitude of the nicotinic fast excitatory postsynaptic potential (EPSP) evoked by stimulation of interganglionic fiber tracts, with a half-maximal inhibitory concentration (EC50) of 300 nM. Norepinephrine did not alter the responsiveness of the neurons to acetylcholine. The alpha 2-adrenoreceptor agonist UK-14304 mimicked the norepinephrine-induced effect with a EC50 of 2.5 nM, whereas alpha 1- and beta-adrenoreceptor agonists had no effect on the EPSP. The alpha 2-adrenoreceptor antagonist idazoxan (1.0 microM) inhibited the UK-14304 response, with a dissociation constant of 1.0 nM. Release of endogenous catecholamines, by the addition of tyramine (100 microM) to the bath, caused an idazoxan-sensitive decrease in the amplitude of the fast EPSP. In the minority of SO neurons that exhibited inhibitory postsynaptic potentials (IPSPs), norepinephrine caused a hyperpolarization of the membrane potential. The IPSP and the norepinephrine-induced hyperpolarization were inhibited by alpha 2-adrenoreceptor antagonists. Desipramine (1.0 microM), an uptake inhibitor, reversibly increased the amplitude of the IPSP. Immunoreactivities for tyrosine hydroxylase and dopamine beta-hydroxylase were coexistent in nerve fibers and nonexistent in cell bodies in the ganglionated plexus of the SO. The results of this study indicate that norepinephrine acts pre- and postsynaptically as an inhibitory neurotransmitter in SO ganglia.
Wells
D G
DG
Department of Anatomy and Neurobiology, College of Medicine, University of Vermont, Burlington 05405.
Mawe
G M
GM
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002395:Catecholamines / Q000378:metabolism; D004299:Dopamine beta-Hydroxylase / Q000378:metabolism; D004594:Electrophysiology; D005724:Ganglia / Q000502:physiology*; D006168:Guinea Pigs; D009638:Norepinephrine / Q000494:pharmacology; D009803:Sphincter of Oddi / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D013565:Sympatholytics / Q000494:pharmacology; D013566:Sympathomimetics / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects; D014439:Tyramine / Q000494:pharmacology; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D002395:Catecholamines; D013565:Sympatholytics; D013566:Sympathomimetics; D014446:Tyrosine 3-Monooxygenase; D004299:Dopamine beta-Hydroxylase; D000109:Acetylcholine; D009638:Norepinephrine; D014439:Tyramine