Journal of Neuroscience, Vol 7, 3783-3792, Copyright © 1987 by Society for Neuroscience
Enhancement of long-term potentiation by cis-unsaturated fatty acid: relation to protein kinase C and phospholipase A2
DJ Linden, FS Sheu, K Murakami and A Routtenberg
Cresap Neuroscience Laboratory, Northwestern University, Evanston, Illinois 60201.
Previous correlative and interventive work from this laboratory has
suggested that activation of protein kinase C (PKC) is important for the
maintenance of the hippocampal long-term potentiation (LTP) response. One
such study demonstrated that application of the cis- unsaturated fatty
acid, oleate, a newly discovered PKC activator, could prolong the time
course of LTP. The present study explored the mechanism of cis-unsaturated
fatty acid action on LTP produced by perforant path stimulation. First,
neither oleate application nor high- frequency stimulation alone produced a
persistent change in synaptic transmission, while the 2 in conjunction did
so. This suggests that oleate acts synergistically with the consequences of
this stimulation to produce an enhancement of the LTP response. Second,
oleate enhancement of LTP was more potent when applied in the perforant
path synaptic terminal zone than in the dentate hilus, implying that the
site of oleate action is at the synapse (where PKC is reported to be
enriched). Third, translocation of PKC activity to the membrane was
significantly increased after oleate-enhanced LTP relative to vehicle
controls. PKC translocation was found to be unaltered by oleate application
alone. Fourth, mepacrine blockade of the Ca2+-dependent enzyme
phospholipase A2, which releases endogenous oleate from membrane
phospholipids, inhibited the time-course of a persistent LTP response. This
inhibition was shown to be reversible with oleate application. We propose
that high-frequency stimulation produces an elevation of intracellular
Ca2+, which then triggers phospholipase A2-mediated oleate release. This
free oleate then could act in synergy with processes that render PKC
oleate-sensitive to produce a persistent activation of PKC, which is
critical for and leads to the persistence of the LTP response.