The Journal of Neurophysiology Vol. 79 No. 2 February 1998, pp. 1113-1116
Copyright ©1998 The American Physiological Society

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Enhancement of Synaptic Excitation by GABA_A Receptor Antagonists in Rat Embryonic Midbrain Culture

Jutta Rohrbacher, Katja Sauer, Andrea Lewen, and Ulrich Misgeld

Physiologisches Institut der Universität Heidelberg, D-69120 Heidelberg, Germany

Rohrbacher, Jutta, Katja Sauer, Andrea Lewen, and Ulrich Misgeld. Enhancement of synaptic excitation by GABA_A receptor antagonists in rat embryonic midbrain culture. J. Neurophysiol. 79: 1113-1116, 1998. Alterations of synaptic excitation induced by exposure to -aminobutyric acid-A (GABA_A) receptor antagonists were investigated employing tight-seal whole cell recording from single neurons or pairs of neurons in rat embryonic midbrain culture. Application of GABA_A receptor antagonists led to sustained depolarizations followed by synchronous paroxysmal depolarization shifts (PDSs). PDSs induced a transient increase in miniature excitatory postsynaptic currents in the presence as well as in the absence of a N-methyl-D-aspartate receptor antagonist. The increase in glutamate release supports the excitatory drive required to reinitiate PDSs from the quiescent interburst intervals. After washout of GABA_A receptor antagonists, synaptic activity remained grouped, regardless of the presence or absence of PDS blockade by tetrodotoxin (TTX). Impediment of action potential-triggered transmitter release by Cd²⁺ or TTX also induced grouped activity. We conclude that changes in synaptic excitation are produced by the impaired GABA_A inhibition per se and by the initiation of PDSs.

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