Differential presynaptic modulation of excitatory and inhibitory autaptic currents in cultured hippocampal neurons

Liu Lin Thio, Kelvin A. Yamada

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Short-term synaptic plasticity has an important role in higher cortical function. Hyperpolarization may effect a form of short-term plasticity by promoting recovery from sodium channel inactivation or by activating axonal A-type potassium channels. To determine whether one or both processes occur, we examined the effect of hyperpolarizing prepulses on autaptic currents in cultured postnatal rat hippocampal neurons. As expected of enhanced recovery from sodium channel inactivation, hyperpolarizing prepulses reversibly increased fast excitatory autaptic currents (eacs) mediated by α-amino-3-hydroxy-5- methyl-4-isoxazolepropionic acid receptors (AMPARs), slow eacs mediated by N-methyl-D-aspartate receptors (NMDARs), and inhibitory autaptic currents (iacs) mediated by γ-aminobutyric acidA receptors (GABA ARs). Hyperpolarizing prepulses augmented nearly all fast and slow eacs but only half of the iacs. This change occurred without a change in autaptic current kinetics. Of note, hyperpolarizing prepulses did not significantly reduce autaptic currents in any neuron studied. The rapidly dissociating competitive antagonists kynurenate and L-2-amino-5-phosphonovaleric acid (LAPV) inhibited fast and slow eacs, respectively, to the same extent with and without a hyperpolarizing prepulse. In addition, hyperpolarizing prepulses revealed a slow eac even after the slow eac evoked without a prepulse was completely blocked by the open channel blocker, (+)-5-methyl-10,11-dihydro-5H- dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801). Finally, hyperpolarizing prepulses did not alter currents evoked by exogenous applications of glutamate and GABA. These findings suggest that hyperpolarizing prepulses preferentially enhance eacs over iacs, and that they do so, in part, by overcoming conduction block or by activating silent synapses.

Original languageEnglish
Pages (from-to)22-28
Number of pages7
JournalBrain Research
Volume1012
Issue number1-2
DOIs
StatePublished - Jun 25 2004
Externally publishedYes

Keywords

  • Conduction block
  • Excitable membranes and synaptic transmission
  • Hyperpolarizing prepulse
  • Presynaptic mechanisms
  • Short-term plasticity
  • Silent synapse
  • Spillover

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