This increase was independent of protein synthesis in response to

This increase was independent of protein synthesis in response to E2 stimulation but was dependent on protein synthesis in response to L1 stimulation (Figure 2G). Similar data were also obtained when L1 was given GLU+SKF stimulation instead of GLU+FSK stimulation (Figures 2H and 2I). In addition, using our uEPSC-potentiation estimation method mentioned above, we found that this change in spine volume at E2 was accompanied by an increase in synaptic strength (Table 1; Figures S3F and S3G). Analogous to STC measured at a population level (Frey and Morris, 1998), STC at the single-spine level is temporally bidirectional as GLU stimulation given to one spine (E1) prior to GLU+FSK stimulation given to a second spine (L2; Figure 2J) resulted

in the expression of L-LTP at both spines (Figure 2K). find more This expression of L-LTP required protein synthesis at L2 (Figure 2L). An important component of STC is that both the synaptic tag and the rate-limiting PrP(s) have limited lifetimes (Frey and Morris, 1997 and Frey and Morris, 1998). However, it has not been determined how different the two lifetimes are, a crucial point in understanding the dynamics of the temporal bidirectionality of STC. To determine the lifetime of the rate-limiting

PrP, we applied GLU+FSK stimulation to two spines (L1, L2) with anisomycin present only during L2 stimulation and varied the time between L1 and L2 stimulations. The efficiency of STC at L2, which would be proportional to the concentration of the rate-limiting PrP (Frey and Morris, 1997), was inversely related to the time between L1 and L2 stimulations (Figure 3A), with STC taking place only if L2 was stimulated within 90 min of L1 stimulation. These data suggest that the rate-limiting PrP decayed within 90 min. We obtained a similar time course of STC when we replaced GLU+FSK stimulation at L2 with GLU stimulation

without anisomycin (E2; Figure 3B). To determine the lifetime of the synaptic tag, we gave GLU stimulation to one spine (E1) before giving GLU+FSK stimulation to a second spine (L2), varying the time between E1 and L2 stimulations. We found that Electron transport chain STC efficiency, which is thought to be a measure of the tag strength (Frey and Morris, 1998), was also inversely related to the temporal interval between E1 and L2 stimulations, with STC occurring fully at an interval of 90 min but being abolished at an interval of 3 hr (Figure 3C). Thus, the temporal bidirectionality of STC is asymmetric as the lifetime of the tag (approximately 120 min, Figure 3C) is different from the lifetime of the rate-limiting PrP (approximately 90 min, Figures 3A and 3B). These data suggest that the temporal order in which information arrives at a dendrite is important in determining how it is consolidated as part of a stable engram. The ability to induce and observe STC at the single-spine level also allowed us to relate the magnitude of E-LTP expression at a single spine to the strength of the synaptic tag.

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