Electrically evoked noradrenaline release from cultured chick sympathetic neurons: modulation via presynaptic alpha-adrenoceptors and lack of autoinhibition.
Sympathetic neurons from twelve day old chick embryos were plated on polystyrol discs and kept in culture for five days. After incubation with 3H-noradrenaline the discs were transferred to small chambers and superfused. Electrical field stimulation (36 pulses at 3 Hz) increased the outflow of tritium. The evoked overflow of tritium was abolished in the absence of extracellular calcium and was diminished by about 90% in the presence of tetrodotoxin (1 mumol/l). The alpha 2-adrenoceptor agonist 5-bromo-6-(2-imidazolin-2-ylamino)quinoxaline (UK-14,304) caused a concentration-dependent decrease in overflow, whereas the alpha 1-adrenoceptor agonist methoxamine was ineffective at up to 1 mumol/l. The concentration-response curve of UK-14,304 was shifted to the right by the alpha 2-adrenoceptor antagonist yohimbine (0.03 mumol/l). Yohimbine on its own caused no significant change. The noradrenaline reuptake inhibitor cocaine (10 mumol/l) caused a small (20%) increase in evoked overflow. The results indicate that cultured chick sympathetic neurons possess release-modulating alpha 2-adrenoceptors and that the electrically induced overflow of transmitter occurs under conditions virtually free of autoinhibition.
Institute of Neuropharmacology, University of Vienna, Austria.
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Böhm
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Huck
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Drobny
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Singer
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D000068438:Brimonidine Tartrate; D002478:Cells, Cultured; D002642:Chick Embryo; D003042:Cocaine / Q000494:pharmacology; D004558:Electric Stimulation; D009474:Neurons / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D011810:Quinoxalines / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D017981:Receptors, Neurotransmitter / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000166:cytology / Q000378:metabolism*; D014316:Tritium; D015016:Yohimbine / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D017981:Receptors, Neurotransmitter; D014316:Tritium; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D003042:Cocaine; D009638:Norepinephrine