Presynaptic inhibition by noradrenaline of the EPSC evoked in neonatal rat sympathetic preganglionic neurons.
Visually identified and electrophysiologically characterized sympathetic preganglionic neurons (SPNs) were recorded using the whole-cell voltage clamp technique in slices of neonatal rat spinal cord. Monosynaptic excitatory postsynaptic currents (EPSCs) were evoked by electrical stimulation of the nucleus intercalatus in the presence of strychnine (5 microM) and bicuculline (10 microM). These EPSCs were abolished by the antagonist of AMPA-type glutamate receptors, 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX; 10 microM). Bath applied noradrenaline (NA; 0.5-50 microM) dose-dependently and reversibly decreased by up to around 60% the amplitude of the EPSC, without affecting the holding current. The EPSC depression by NA was not accompanied by a change in EPSC reversal potential (around +5 mV), nor were inward currents generated by pressure application of glutamate affected by NA application. A comparable degree of EPSC depression was also seen with the alpha2-adrenoceptor agonist clonidine (5 microM), and the alpha2A-agonist oxymetazoline (5 microM), while the alpha1-agonist phenylephrine (100 microM) caused only a 22% depression. The EPSC depression caused by NA (10 microM) was completely antagonized by either the alpha-antagonist phentolamine (10 microM) or the alpha2-antagonist idazoxan (2 microM). Conversely, the beta-adrenoceptor antagonist popranolol (5 microM), and the alpha1-, alpha2B- and alpha2C-antagonist prazosin (2 microM) were without effect. These results indicate that activation of presynaptic alpha2A-adrenoceptors on inputs to SPNs decreases glutamate release.
Miyazaki
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T
Department of Physiology, Tokyo Medical College, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo 160, Japan. t.miyazaki@bham.ac.uk
Kobayashi
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H
Tosaka
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D000320:Adrenergic Fibers / Q000187:drug effects / Q000502:physiology*; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D003000:Clonidine / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects* / Q000502:physiology; D018698:Glutamic Acid / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D009924:Organ Culture Techniques; D010109:Oxymetazoline / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000502:physiology; D013116:Spinal Cord / Q000737:chemistry / Q000166:cytology
C547770:Adra2a protein, rat; D058647:Adrenergic alpha-2 Receptor Agonists; D058669:Adrenergic alpha-2 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D010656:Phenylephrine; D018698:Glutamic Acid; D010109:Oxymetazoline; D003000:Clonidine; D009638:Norepinephrine; D011224:Prazosin