Abstract
Rhythmic activity induced by different combinations of N-methyl-D-aspartate (NMDA), serotonin (5-HT), muscarine and D-tubocurarine was monitored intracellularly in lumbar motoneurons in a slice preparation from adult turtles. Low concentration of NMDA (7.5-15 microM) combined with 5-HT (10-80 microM) induced rhythmic motoneuron discharge which was underlied by intrinsic voltage oscillations resistant to tetrodotoxin. This oscillatory activity was abolished by 2-amino-5-phosphonopentanoic acid (AP5), a competitive blocker of NMDA receptors and by nifedipine a selective blocker of L-type calcium channels. In contrast, rhythmicity induced by the cholinergic agents muscarine and d-tubocurarine was abolished by nifedipine but not by AP5 nor by high [Mg2+]o. These results show that different receptor agonists induce intrinsic oscillations in mature motoneurons by independent routes. Each oscillatory mechanism depends on L-type calcium channels but only NMDA/5-HT-induced oscillations depend on voltage-sensitive NMDA-activated ionophores.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Calcium Channel Blockers / pharmacology
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Calcium Channels / physiology*
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Calcium Channels, L-Type
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Cholinergic Fibers / chemistry*
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Cholinergic Fibers / drug effects
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Cholinergic Fibers / physiology
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Dihydropyridines / pharmacology
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Excitatory Amino Acid Agonists / pharmacology
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Magnesium / pharmacology
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Motor Neurons / chemistry
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Motor Neurons / physiology*
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Motor Neurons / ultrastructure
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Muscarine / pharmacology
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Muscarinic Agonists / pharmacology
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N-Methylaspartate / pharmacology
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Nicotinic Antagonists / pharmacology
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Nifedipine / pharmacology
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Organ Culture Techniques
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Periodicity
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Receptors, N-Methyl-D-Aspartate / agonists
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Receptors, N-Methyl-D-Aspartate / physiology*
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Serotonin / pharmacology
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Spinal Cord / chemistry
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Spinal Cord / cytology
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Spinal Cord / physiology*
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Tetrodotoxin / pharmacology
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Tubocurarine / pharmacology
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Turtles
Substances
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Calcium Channel Blockers
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Calcium Channels
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Calcium Channels, L-Type
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Dihydropyridines
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Excitatory Amino Acid Agonists
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Muscarinic Agonists
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Nicotinic Antagonists
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Receptors, N-Methyl-D-Aspartate
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Serotonin
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Tetrodotoxin
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N-Methylaspartate
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1,4-dihydropyridine
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Muscarine
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Magnesium
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Nifedipine
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Tubocurarine