Figure 3. Presynaptic local protein synthesis is required for the development of synaptic resistance to depotentiation stimulation.

A, summary of experiments showing that LFS given 10 min after two trains of 100 Hz HFS almost completely reversed LTP (n = 4; •), whereas EPSCs in slices that received HFS without LFS exhibited persistent potentiation (n = 6; ○). Whole-cell patch clamp recordings were made of CA3 pyramidal cells at a holding potential of −70 mV. B, summary of experiments showing that the synaptic resistance to LFS-DEP was not affected by postsynaptic injection of the cap analogue m⁷ GpppG. Whole-cell patch clamp recordings were made of CA3 pyramidal cells at a holding potential of −70 mV. When LFS was applied 10 min after four trains of 100 Hz HFS in CA3 pyramidal cells loaded with m⁷ GpppG (250 μm) (n = 6; •), transient synaptic depression was seen, but EPSCs recovered to potentiated levels not significantly different those seen in control cells without m⁷ GpppG (n = 6; ○). C, summary of experiments showing that CA1 LTD induced by DHPG (50 μm, 5 min) was prevented by postsynaptic injection of m⁷ GpppG (250 μm) (n = 6; •). Whole-cell patch clamp recordings were made of CA1 pyramidal cells at a holding potential of −70 mV. D1, schematic diagram showing the incision (thick black line) made to transect mossy fibre axons from the granule cell somata and the positions of recording (Rec) and stimulation (Stim) electrodes. D2, bright-field image of a hippocampal slice after the isolation of mossy fibre axons from the granule cell somata. Arrows indicate the site of lesion. Scale bar, 500 μm. E1, schematic diagram showing a mossy fibre axon transection slice, where an electrical stimulus was delivered to the stratum lucidum of the CA3 region and the evoked antidromic population spikes were recorded from the granulosum of the dentate gyrus (DG). E2, absence of antidromic population spikes in stratum granulosum of the dentate gyrus when stimulation was applied at the stratum lucidum of the CA3 region in the mossy fibre axon transection slice, whereas an antidromic population spike was successfully evoked in control slices. F, summary of experiments showing that mossy fibre axon transection had no effect on either the synaptic resistance to LFS-DEP (n = 6; •) or the induction of LTP (n = 8; ○). G, summary of experiments showing that preincubation of mossy fibre axon transection slices with protein synthesis inhibitor anisomycin (20 μm; 60 min) permitted persistent LFS-DEP of four trains of 100 Hz LTP (n = 6; •) but had no effect on the induction of LTP (n = 6; ○).