Mechanisms for regulating synaptic efficiency in the visual cortex

M. J. Friedlander, K. Harsanyi, P. Kara

Research output: Contribution to journalArticlepeer-review

7 Scopus citations

Abstract

Brief epochs of pairing of low frequency synaptic activation and postsynaptic depolarization, in vitro, in supragranular neurons of mature guinea-pig visual cortex lead to a transient (20-60 min) synaptic potentiation. This process is due to a true up-regulation of excitatory synapse efficiency onto the activated neuron. The potentiation requires NMDA receptor activation and a postsynaptic calcium signal for induction and it is modifiable by endogenous nitric oxide (NO) production in the mature cortex. In the cortex of young animals (< PND 21), the pairing-induced potentiation is robust and depends on a postsynaptic calcium signal but it is independent of NMDA receptor activation and NO production. The ability of cortical synaptosomes to release endogenous glutamate is enhanced by NMDA receptor activation and this enhancement is NO-dependent. The NO signal, however, does not amplify the glutamate release of all synapses but only those that have activated voltage-gated calcium channels and were presumably more active at the time of the NO signal. Electrophysiological recordings from visual cortical neurons in anesthetized cats with local iontophoresis of compounds that inhibit or facilitate endogenous cortical NO production reveal the capacity for NO to modulate visual responses in vivo. NO appears to act in the intact cortex by amplifying signals of visual inputs that were co-active at the time of the NO production. The adult visual cortex is capable of dramatic alterations in synaptic efficiency over brief periods suggesting a dynamic cortical network. NMDA receptors and nitric oxide contribute to these processes.

Original languageEnglish (US)
Pages (from-to)179-184
Number of pages6
JournalJournal of Physiology Paris
Volume90
Issue number3-4
DOIs
StatePublished - Jan 1 1996
Externally publishedYes

Keywords

  • Adult plasticity
  • Hebbian synapse
  • Long-term potentiation
  • NMDA receptors
  • Nitric oxide
  • Synchrony
  • Visual cortex

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