Blocking TNFα activity prevented the heterodendritic metaplasticity effect at SR synapses. a, Priming-mediated inhibition of LTP was significantly reduced by the TNFα Ab treatment (25 μg/50 ml), although not completely. b, In contrast, priming stimulation elicited homosynaptic LTP in SO, which was unaltered by the TNFα Ab treatment. c, Preincubating slices with the TNFα Ab (25 μg/ml) completely prevented the inhibition of LTP in SR due to priming in SO. d, However, SO LTP remained unaltered by the TNFα Ab preincubation treatment. e, Application of thalidomide throughout the experiment prevented the inhibition of LTP in SR due to priming in SO. f, LTP in SO was unaltered by thalidomide treatment. *p < 0.05. Data are mean ± SEM. n = 7–9 slices per group. Inset, Representative waveforms for the figures are averages of the final 10 sweeps taken before (pre) and 50–60 min after TBS (post) for SR and 80–90 min after HFS (post) for SO graphs, respectively. The numbers above the waveforms correspond to the treatment group, as indicated in the figure legend.