The Journal of Neuroscience, November 15, 2000, 20(22):8528-8532
Protein Synthesis Inhibition Blocks the Induction of Mossy Fiber
Long-Term Potentiation In Vivo
Edwin J.
Barea-Rodríguez,
Domingo T.
Rivera,
David B.
Jaffe, and
Joe L.
Martinez Jr
University of Texas at San Antonio, Division of Life Sciences, San
Antonio, Texas 78249
Protein synthesis inhibitors block the maintenance of NMDA
receptor-dependent long-term potentiation (LTP) both in
vivo and in vitro. Protein synthesis inhibitors
block mossy fiber(MF) LTP maintenance in vitro, but
little is known about the effect of protein synthesis inhibitors on
either induction or maintenance in MF-LTP in vivo. Here
we study the role of protein synthesis in the induction of long-term
potentiation at the mossy fiber-CA3 hippocampal synapse in
vivo in anesthetized rats. The protein synthesis inhibitor
anisomycin was administered at different doses (0.04, 10, or 40 nmol)
into area CA3 15 min before delivering high-frequency stimulation (two
times at 100 Hz, 1 sec). Anisomycin blocked MF-LTP induction in
a dose-dependent manner; both 40 and 10 nmol blocked MF-LTP induction,
but a lower dose of 0.04 nmol was without effect. The inhibitory effect
of anisomycin on protein synthesis was determined by measuring the
incorporation of [35S]methionine into the
newly synthesized proteins. Percentages of protein synthesis inhibition
were determined by comparing [35S] incorporation
of anisomycin-treated samples with vehicle controls. Doses of 0.04, 10, or 40 nmol of anisomycin produced 21, 82, or 83% inhibition of
[35S]methionine incorporation, respectively. The
effect of anisomycin was verified using a single dose of the protein
synthesis inhibitor cycloheximide (40 nmol). Cycloheximide also blocked
MF-LTP induction. These results suggest that protein synthesis plays an
important role in the induction of mossy fiber long-term potentiation
in vivo.
Key words:
anisomycin; CA3; mossy fibers; hippocampus; long-term
potentiation; cycloheximide and opioids
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