Fig. 2

Synaptic profiles sampled from stratum radiatum of the CA1 region of hippocampal slice cultures under control conditions (a) and upon 30 s (b) and 2 min (inset in b) of depolarization with high K⁺ (90 mM). PSDs (arrows) showed a slight increase in thickness in b over a, and a more conspicuous thickness in inset in b over a. The curvature of the PSDs was in different directions in a vs. b. The presynaptic terminals arched into the postsynaptic elements slightly in a, while the reverse occurred in b. Double arrows in b points to double-membraned invaginations in the presynaptic terminals termed “spinules”, an activity-induced structure only seen in stimulated samples [9]. Scale bar = 0.5 μm