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The mechanism of cAMP-mediated enhancement at a cerebellar synapse.

Authors
  • Chen, C1
  • Regehr, W G
  • 1 Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA.
Type
Published Article
Journal
Journal of Neuroscience
Publisher
Society for Neuroscience
Publication Date
Nov 15, 1997
Volume
17
Issue
22
Pages
8687–8694
Identifiers
PMID: 9348337
Source
Medline
Language
English
License
Unknown

Abstract

Increases in cAMP have been shown previously to enhance the strength of the granule cell to Purkinje cell synapse. We have examined the mechanisms underlying this enhancement in rat cerebellar brain slices. Elevation of cAMP levels by forskolin increased synaptic currents in a dose-dependent manner. Fluorometric calcium measurements revealed that forskolin did not affect presynaptic calcium influx or resting calcium levels. The waveform of the presynaptic volley was also unaltered, indicating that changes in the presynaptic action potential did not contribute to synaptic enhancement. However, forskolin enhanced the frequency but not the size of spontaneous miniature EPSCs. There was a one-to-one correspondence between increases of spontaneous and evoked neurotransmitter release. These results suggest that forskolin increases release at this synapse via presynaptic mechanisms that do not alter calcium influx. The effect of forskolin on paired-pulse facilitation was examined to assess the relative contributions of changes in the probability of release (p) and changes in the number of functional release sites (n) to this form of enhancement. These experiments suggest that although small changes in n cannot be excluded, most of the enhancement arises from increases in p.

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