Abstract
In the presence of 4-aminopyridine (4-AP) and excitatory amino acid receptor blockers, GABAergic networks in the neocortex give rise to large spontaneous GABA-mediated depolarizations. We used voltage-sensitive dye techniques to explore the network properties of depolarizing GABA responses. Voltage-sensitive dye signals demonstrated that the superficial layers support the propagation of depolarizing GABA responses, with only minimal signals detected in deeper cortical layers. GABA responses propagated at a speed of 2.7 +/- 0.2 mm/s, a rate intermediate to fast synaptic transmission and spreading depression. Changes in the extracellular potassium concentration altered the propagation speed of the depolarizing GABA response. Taken together, these data support a role for both direct synaptic action of GABA at GABA(A) receptors and nonsynaptic mechanisms in the generation and propagation of depolarizing GABA responses.
Publication types
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Comparative Study
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Research Support, N.I.H., Extramural
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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4-Aminopyridine / pharmacology
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6-Cyano-7-nitroquinoxaline-2,3-dione / pharmacology
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Animals
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Animals, Newborn
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Diagnostic Imaging / methods
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Dose-Response Relationship, Drug
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Drug Interactions
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Evoked Potentials / drug effects
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Evoked Potentials / physiology
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Excitatory Amino Acid Antagonists / pharmacology
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Fluorescent Dyes / metabolism
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Fluorescent Dyes / pharmacology
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In Vitro Techniques
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Kynurenic Acid / pharmacology
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Linear Models
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Neocortex / drug effects
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Neocortex / physiology*
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Nerve Net / drug effects
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Nerve Net / physiology*
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Neural Inhibition / drug effects
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Neural Inhibition / physiology*
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Potassium Channel Blockers / pharmacology
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Pyridinium Compounds / metabolism
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Pyridinium Compounds / pharmacology
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Rats
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Reaction Time / drug effects
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Time Factors
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gamma-Aminobutyric Acid / pharmacology
Substances
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Excitatory Amino Acid Antagonists
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Fluorescent Dyes
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Potassium Channel Blockers
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Pyridinium Compounds
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gamma-Aminobutyric Acid
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6-Cyano-7-nitroquinoxaline-2,3-dione
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4-Aminopyridine
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Kynurenic Acid
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RH 414