(A–C) Relative densities of β2/3 subunit-containing
clusters with presynaptic contacts. Synaptically located receptors
increase with increasing age of the cultures. However, the majority of
all β2/3 clusters are lacking presynaptic partners even in
well-differentiated cultures. Colocalizations with FM4-64 or
SV2-positive synapses are maximal at day 30 (A and
B). The highest density of synaptic β2/3 clusters at
GABAergic terminals was measured on day 20 (C).
*, P < 0.05; ***,
P < 0.001 vs. day 10. †, P <
0.05 vs. day 30. (D–F) Relative densities of γ2
subunit-containing clusters with presynaptic contacts. Synaptic
receptor clusters containing γ2 increase with increasing age of the
cultures, although the majority of the clusters remain without a
presynaptic partner, even in mature cultures on day 30. With
GAD-stained synapses, the density is highest on day 20
(F). ***, P <
0.0001 vs. day 5; †, P < 0.002 vs. day 10 and
P < 0.05 vs. day 20; **,
P < 0.02 vs. day 10; §, P <
0.0001 vs. days 5 and 10.