Differential role of pre- and postsynaptic neurons in the activity-dependent control of synaptic strengths across dendrites
Fig 5
Uniform downscaling of postsynaptic AMPA receptors across the dendritic tree in primary hippocampal cultures.
(A) Scheme to visualize individual postsynaptic strengths of stimulated and nonstimulated synapses. (B) Representative EPSC trace evoked by a pair of brief depolarizations (+100 mV, 50-ms interval) of the presynaptic neuron. (C–D) Time course of EPSC amplitude (C) and PPR (D) from an example recording. (E) Fluorescence image of a SEP-GluA2–expressing postsynaptic neuron (yellow) receiving putative synaptic contacts from an axon of a neuron filled with an Alexa Fluor dye (blue). Scale bar, 40 μm. (F) Details of the boxed area in (E). Arrowheads indicate putative synaptic contacts between the stimulated presynaptic cell and the postsynaptic cell. Scale bar, 10 μm. (G) Illustration of the basis for discriminating between stimulated and nonstimulated synapses. SEP-GluA2 puncta apposed to the labeled axon are considered as stimulated synapses, while the others are considered as nonstimulated. (H) Time-lapse images of color-coded fluorescence intensity showing the decrease of SEP-GluA2 signal after the conditioning stimulation for the area corresponding to (F). Individual SEP-GluA2 puncta associated to the labeled axon shown in (F) are indicated (arrowheads). Scale bar, 10 μm. (I,J) Time course of SEP-GluA2 fluorescence intensity at putative stimulated synapses (I: paired, two-tailed Student t test, ****p < 0.0001, n = 12 synapses) and nonstimulated synapses (J: paired, two-tailed Student t test, ****p < 0.0001, n = 34 synapses) for the same postsynaptic neuron. (K,L) Plots of the SEP-GluA2 fluorescence intensity before versus after the stimulation at stimulated synapses and nonstimulated synapses for the same example in (E–J) (K: R2 = 1.00; L: R2 = 0.92, p < 0.0001). (M) Comparison of the extent change in fluorescence intensity of SEP-GluA2 at stimulated versus nonstimulated synapses (R2 = 0.77, p = 0.0209, n = 6 cells), with linear regression shown. Data are expressed as mean ± SEM. m indicates the slope. (N) Comparison of the extent change in fluorescence intensity of SEP-GluA2 versus PPR change at stimulated synapses (R2 = 0.77, p = 0.0209, n = 6 cells), with linear regression shown. m indicates the slope. Underlying data can be found in S1 Data. AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; AP, action potential; a.u., arbitrary unit; EPSC, excitatory postsynaptic current; GluA, AMPA receptor subunit; PPR, paired-pulse ratio; SEP, superecliptic pHluorin; stim, stimulation.