Photolysis of postsynaptic caged Ca2+ can potentiate and depress mossy fiber synaptic responses in rat hippocampal CA3 pyramidal neurons

J Neurophysiol. 2004 Apr;91(4):1596-607. doi: 10.1152/jn.01073.2003. Epub 2003 Nov 26.


The induction of mossy fiber-CA3 long-term potentiation (LTP) and depression (LTD) has been variously described as being dependent on either pre- or postsynaptic factors. Some of the postsynaptic factors for LTP induction include ephrin-B receptor tyrosine kinases and a rise in postsynaptic Ca2+ ([Ca2+]i). Ca2+ is also believed to be involved in the induction of the various forms of LTD at this synapse. We used photolysis of caged Ca2+ compounds to test whether a postsynaptic rise in [Ca2+]i is sufficient to induce changes in synaptic transmission at mossy fiber synapses onto rat hippocampal CA3 pyramidal neurons. We were able to elevate postsynaptic [Ca2+]i to approximately 1 microm for a few seconds in pyramidal cell somata and dendrites. We estimate that CA3 pyramidal neurons have approximately fivefold greater endogenous Ca2+ buffer capacity than CA1 neurons, limiting the rise in [Ca2+]i achievable by photolysis. This [Ca2+]i rise induced either a potentiation or a depression at mossy fiber synapses in different preparations. Neither the potentiation nor the depression was accompanied by consistent changes in paired-pulse facilitation, suggesting that these forms of plasticity may be distinct from synaptically induced LTP and LTD at this synapse. Our results are consistent with a postsynaptic locus for the induction of at least some forms of synaptic plasticity at mossy fiber synapses.

Publication types

  • Comparative Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Analysis of Variance
  • Animals
  • Animals, Newborn
  • Anticonvulsants / pharmacology
  • Benzothiazoles
  • Calcium / metabolism*
  • Coumarins / metabolism
  • Cyclopropanes / pharmacology
  • Cyclosporine / pharmacology
  • Electric Stimulation / methods
  • Enzyme Inhibitors / pharmacology
  • Excitatory Postsynaptic Potentials / physiology
  • Glycine / analogs & derivatives*
  • Glycine / metabolism
  • Glycine / pharmacology
  • Hippocampus / cytology*
  • Hippocampus / physiology
  • In Vitro Techniques
  • Long-Term Potentiation / physiology
  • Long-Term Potentiation / radiation effects
  • Long-Term Synaptic Depression / physiology*
  • Long-Term Synaptic Depression / radiation effects
  • Marine Toxins
  • Mossy Fibers, Hippocampal / physiology*
  • Mossy Fibers, Hippocampal / radiation effects
  • Oxazoles / pharmacology
  • Patch-Clamp Techniques / methods
  • Photolysis*
  • Pyramidal Cells / physiology*
  • Rats
  • Rats, Sprague-Dawley
  • Synapses / physiology*
  • Synaptic Transmission / physiology


  • Anticonvulsants
  • Benzothiazoles
  • Coumarins
  • Cyclopropanes
  • Enzyme Inhibitors
  • Marine Toxins
  • N-(3-(2-benzothiazolyl)-6-(2-(2-(bis(carboxymethyl)amino)-5-methylphenoxy)ethoxy)-2-oxo-2H-1-benzopyran-7-yl)-N-(carboxymethyl)glycine
  • Oxazoles
  • 2-(2,3-dicarboxycyclopropyl)glycine
  • calyculin A
  • Cyclosporine
  • Calcium
  • Glycine