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. Author manuscript; available in PMC: 2012 Feb 17.
Published in final edited form as: J Neurosci. 2011 Aug 17;31(33):11762–11771. doi: 10.1523/JNEUROSCI.2707-11.2011

Figure 5. TrkB as synaptic tag for L-LTP.

Figure 5

(A) Two-pathway recording scheme. Two independent Schafer collateral pathways that project to the same CA1 neurons were stimulated by two stimulating electrodes positioned on either side of the recording electrode. S1 was stimulated by strong TBS (12TBS) whereas S2 was stimulated by weak TBS (4TBS).

(B) Lack of facilitation between the two Schafer collateral pathways. Upper: the superimposed red and green fEPSP traces induced by S2 were same, regardless of whether S1 was stimulated 30 msec earlier. Lower: S1-induced fEPSPs were the same regardless of S2 stimulation.

(C) Failure to induce L-LTP by weak TBS (4TBS). Application of 4TBS alone induced only E-LTP (last <2 hours), but not L-LTP.

(D) Weak TBS in S2 induced L-LTP when preceded by strong TBS in S1. In a typical “two pathway” experiment using slices from TrkBF616A mice, a 12TBS to S1 was followed by a 4TBS to S2. Application of 12TBS resulted in a robust L-LTP in S1. Application of 4TBS to S2, which normally induces only E-LTP, now elicited L-LTP. Treatment with vehicle (indicated by the black bar) around the time of 4TBS had no effect on L-LTP in TrkBF616A slices.

(E) Inhibition of TrkB activation blocked E-LTP → L-LTP conversion in S2. The “two-pathway” experiment was done exactly the same way as in (D), except 1NMPP1 (5 µM) was applied instead of vehicle (DMSO). Treatment with 1NMPP1 blocked L-LTP in S2, without affecting L-LTP in S1 in TrkBF616A slices.

(F) Lack of effect of 1NMPP1 on L-LTP in wild type hippocampal slices. 1NMPP1 was applied to hippocampal slices from C57BL/6 mice around the time of 4TBS (black bar). 12TBS induced a 166±10% potentiation in S1, whereas 4TBS induced a 138±5% potentiation in S2.

(G) Lack of effect of vehicle on L-LTP in TrkBF616A slices. L-LTP was induced in both S1 (158±9%) and S2 (135±10%) when vehicle was applied at the time of 12TBS.

(H) 1NMPP1 inhibited L-LTP in S1 (104±5%) but left L-LTP intact in S2 (135±5%) when it was applied at the time of 12TBS.

The number of slices tested is indicated in brackets. At least 3 animals were tested for each experiment.