title: Arachidonic acid, but not sodium nitroprusside, stimulates presynaptic protein kinase C and phosphorylation of GAP-43 in rat hippocampal slices and synaptosomes.
abstract: Activation of protein kinase C (PKC) and phosphorylation of its presynaptic substrate, the 43-kDa growth-associated protein GAP-43, may contribute to the maintenance of hippocampal long-term potentiation (LTP) by enhancing the probability of neurotransmitter release and/or modifying synaptic morphology. Induction of LTP in rat hippocampal slices by high-frequency stimulation of Schaffer collateral-CA1 synapses significantly increased the PKC-dependent phosphorylation of GAP-43, as assessed by quantitative immunoblotting with a monoclonal antibody that recognizes an epitope that is specifically phosphorylated by PKC. The stimulatory effect of high-frequency stimulation on levels of immunoreactive phosphorylated GAP-43 was not observed when 4-amino-5-phosphonovalerate (50 microM), an N-methyl-D-aspartate (NMDA) receptor antagonist, was bath-applied during the high-frequency stimulus. This observation supports the hypothesis that a retrograde messenger is produced postsynaptically following NMDA receptor activation and diffuses to the presynaptic terminal to activate PKC. Two retrograde messenger candidates--arachidonic acid and nitric oxide (sodium nitroprusside was used to generate nitric oxide)--were examined for their effects in hippocampal slices on PKC redistribution from cytosol to membrane as an indirect measure of enzyme activation and PKC-specific GAP-43 phosphorylation. Bath application of arachidonic acid, but not sodium nitroprusside, at concentrations that produce synaptic potentiation (100 microM and 1 mM, respectively) significantly increased translocation of PKC immunoreactivity from cytosol to membrane as well as levels of immunoreactive, phosphorylated GAP-43. The stimulatory effect of arachidonic acid on GAP-43 phosphorylation was also observed in hippocampal synaptosomes. These results indicate that arachidonic acid may contribute to LTP maintenance by activation of presynaptic PKC and phosphorylation of GAP-43 substrate. The data also suggest that nitric oxide does not activate this signal transduction system and, by inference, activates a distinct biochemical pathway.
authors.affiliation: Department of Pharmacology, State University of New York Health Science Center at Syracuse 13210-1605.
authors.forename: Y
authors.initials: Y
authors.lastname: Luo
authors.forename: M L
authors.initials: ML
authors.lastname: Vallano
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D006152:Cyclic GMP / Q000378:metabolism; D005260:Female; D019922:GAP-43 Protein; D006624:Hippocampus / Q000378:metabolism* / Q000502:physiology; D015151:Immunoblotting; D066298:In Vitro Techniques; D017774:Long-Term Potentiation; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009599:Nitroprusside / Q000494:pharmacology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D017729:Presynaptic Terminals / Q000201:enzymology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013574:Synaptosomes / Q000378:metabolism
chemical_list: D019922:GAP-43 Protein; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D010750:Phosphoproteins; D009599:Nitroprusside; D016718:Arachidonic Acid; D011493:Protein Kinase C; D006152:Cyclic GMP