Figure 1.

LTPi depends on postsynaptic activity and is connection-specific. A, Top, Sample traces of monosynaptic IPSPs before (black) and after (gray) induction. Induction paradigms used in those experiments were 8 Hz (Bc, left) and 50 Hz (Bg, right). See B for further description of induction paradigms. A, Bottom, Time course of percentage changes in IPSP amplitude induced with four different paradigms. B, Bar plot of the magnitude of LTPi versus postsynaptic neurons activity for all pairs tested. Postsynaptic action potentials were elicited with 3 ms pulses delivered on top of a depolarizing step that was adjusted to achieve similar depolarization levels. Induction paradigms consist of 20 repetitions of the pairing shown at the bottom of each bar. The frequency of repetition was 0.1 Hz. C, Left, Diagram of experimental configuration and sample traces of a FS neuron connected to three pyramidal neurons. Pairings Ba, Bb, and Bd were applied at the three different connections. C, Right, Sample traces before (black) and after (gray) LTPi induction with the pairing shown in the diagram. Note the successful induction of LTPi only with pairings Ba and Bb onto Pyr 1 and Pyr 2. D, Bar plot of average percentage changes in IPSP amplitude induced by pairings Ba–Bc, black bar; and pairings Bd–Bg, gray bar. Data from multiple triplets/quadruplets were pooled in the average bar plot. Right, Bar plot of the average change in IPSP amplitude in Ba–Bc (black; n = 7) and Bd–Bg pairings (gray; n = 6). Data are presented as mean ± SE. Asterisks indicate significant differences. To favor readability asterisks were not added to highlight significant differences in A. The p values of one-way ANOVA and post hoc t tests are reported in Results.