Pre-LTP in thalamic input depends on synaptic activity at cortico-LA synapses.

<p><b>A</b>, Schematic representation of the induction protocol used in this experiment. Double arrows indicate the induction protocols consisting of paired stimulation of both thalamic and cortical inputs without postsynaptic depolarization. <b>B</b>, <b>C</b>, An individual experiment (<b>B2, C2</b>) investigating whether LTP could be induced or not by the induction when the amplitude of cortical EPSC is smaller (<b>B1</b>) or larger (<b>C1</b>) than that of thalamic. <b>D</b>, An individual LTP experiment (<b>D2</b>) showing effect of D-AP5 on the non-potentiated EPSC (<b>C2</b>). Insets (<b>B1-D1</b>): EPSCs in both thalamic and cortical inputs before the induction. Insets (<b>B2-D2</b>): averaged EPSCs before (1) and after (2) delivery of the induction (double arrows). Scale bar (<b>B</b>-<b>D</b>) 50 pA, 20 ms. <b>E</b>, Relationship between C/T ratio (before the induction) and the magnitude of LTP in thalamic input induced the induction with (open circles) or without D-AP5 (closed circles) in the bath solution. Each symbol represents a separate experiment. <b>F</b>-<b>H</b>, Summary graphs of LTP experiments (<b>B</b>-<b>D</b>) EPSCs observed with C/T in a range below 1.5 resulted in robust potentiation (<b>F</b>: 152 ± 8% of baseline, n=10, paired <i>t</i> test, p<0.01 versus baseline). When the data were collected in a range of C/T > 1.5, lesser LTP was observed (<b>G</b>, 110 ± 4% of baseline, n=19, paired t test, p=0.045 versus baseline). In the same range of C/T, the EPSCs were significantly potentiated by addition of D-AP5 (<b>H</b>, 185 ± 11% of baseline, n=13, paired <i>t</i> test, p<0.01 versus baseline). <b>I</b>, This observed potentiation was resistant to BAPTA (20 mM) (180 ± 36% of baseline, n=6, p=0.85 versus control by unpaired <i>t</i> test), but was blocked by BAPTA-AM (50 µM) (100 ± 13% of baseline, n=5, p<0.01 versus control by unpaired <i>t</i> test). <b>J</b>, LTP_ct was completely blocked by either UBP296 (1 µM) (100 ± 7% of baseline, n=4, p<0.01 versus control by unpaired <i>t</i> test) or ACET (0.5 µM) (103 ± 10% of baseline, n=5, p<0.01 versus control by unpaired <i>t</i> test). Insets: superimposed averaged EPSCs recorded before and after the induction with application of each drug. Scale bars: 50 pA, 20 ms. <b>K</b>, Quantification of pharmacological experiment results (<b>H</b>, <b>I</b>, <b>J</b>). Control was obtained from the result in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0074668#pone-0074668-g004" target="_blank">Figure <b>4H</b></a>. **p<0.01; unpaired <i>t</i> test.