Post- and presynaptic effects of norepinephrine in guinea-pig colonic submucous plexus.
Intracellular recording techniques were used to investigate the effects of norepinephrine on submucous neurones in the guinea-pig distal colon. In 81% of the neurones, pressure microejection of norepinephrine produced a membrane hyperpolarization associated with a decrease in excitability and input resistance. Microejection of clonidine (1 microM) mimicked the norepinephrine-induced hyperpolarization, whereas both phentolamine (1 microM) and yohimbine (1 microM) reversibly suppressed it. Superfusion of norepinephrine (1 nM - 10 microM) hyperpolarized the cells in a concentration-dependent manner. Norepinephrine and clonidine (1 nM - 10 microM) caused a concentration-dependent presynaptic inhibition of stimulus-evoked cholinergic fast excitatory postsynaptic potential. Slow inhibitory post-synaptic potentials (sISPSs) were induced by focal electrical stimulation of the interganglionic fibre tracts in 43% of the neurones tested. Superfusion of both phentolamine (1 microM) and yohimbine (1 microM) reduced the sIPSPs while prazosin (1 microM) had no significant effect. We concluded that norepinephrine acted post- and presynaptically via alpha 2-adrenoreceptors to have an inhibitory effect on the guinea-pig colonic submucous. In addition, our study strongly supported the role of norepinephrine as a mediator of the sIPSPs. As a result, norepinephrine would primarily suppress information transfer within the neuronal circuits in guinea-pig colonic submucosal plexus.
Dobreva
G
G
Department of Physiology, School of Veterinary Medicine, Hannover, Germany.
Neunlist
M
M
Frieling
T
T
Schemann
M
M
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D003106:Colon / Q000294:innervation*; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects*; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008839:Microelectrodes; D009130:Muscle, Smooth / Q000294:innervation; D009197:Myenteric Plexus / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
D015016:Yohimbine; D003000:Clonidine; D000109:Acetylcholine; D009638:Norepinephrine; D011224:Prazosin; D010646:Phentolamine