Botulinum Toxin type A pretreatment markedly reduces induction of LTD, but not LTP, at Schaffer collateral-CA1 synapses.

<p><b>A</b>: Time course of reduction in field excitatory postsynaptic potential (fEPSP) slopes recorded in CA1 <i>stratum radiatum</i> and induced by bath application of BotoxA (200 ng/ml, 90 min; grey bar), plotting normalized fEPSP slopes (<i>n</i> = 9 slices). <b>B</b>: Time course of the effect of low frequency Schaffer collateral stimulation (2 Hz/10 min, solid bar) on fEPSP slopes in field CA1 of slices (<i>n</i> = 6) pretreated for 90 min with BotoxA (200 ng/ml), which eliminated LTD (<i>P</i><0.01; Student’s t-test compared to untreated slice LTD). <b>C</b>: Time course of LTP elicited in field CA1 by four trains of theta burst Schaffer collateral stimulation (arrow; each train 10 bursts of 4 stimuli at 100 Hz frequency, 200 ms interburst interval) in slices (<i>n</i> = 6) pretreated for 90 min with BotoxA (200 ng/ml). <b>D</b>: Time course of the magnitude of depotentiation, where BotoxA (200 ng/ml, grey bar) was bath applied for 90 min prior to induction of LTP by high-frequency theta burst stimulation (arrow; 4 trains of 10 4×100 Hz bursts, 200 ms interburst interval). After LTP was established for 30 min, low frequency Schaffer collateral stimulation (2 Hz/10 min, solid bar) elicited significant depotentation reversal of LTP (<i>n</i> = 6). Each point mean ± SEM of <i>n</i> slices. Representative fEPSP waveforms insets recorded at times indicated by numbers on traces and time course.