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Fig. 3. AChR-ß3F/3F mice fail to form
morphologically complex synapses. (A-H) Confocal images of
synapses, stained with Alexa Fluor 594- -BGT, in the diaphragm muscle
from P30 wild-type and AChR- ß3F/3F mice.
E-H are higher magnification images of the boxed regions in A-D. Scale bar: 10
µm for A-D and 5 µm for E-H. (I) At category 1 synapses, >75%
of the surface area is covered with AChR striations; at category 2 synapses,
25-75% of the surface area is covered with AChR striations; at category 3
synapses, <25% of the surface area is covered with AChR striations.
AChR-ß3F/3F mice have fewer category 1
synapses and more category 3 synapses than wild-type mice. Wild type: 39
category 1 synapses, 20 category 2 synapses, 0 category 3 synapses;
AChR-ß3F/3F: 1 category 1 synapse, 18
category 2 synapses, 36 category 3 synapses; P<0.005,
 2 test. (J) Two or fewer gaps are evident at category 1
synapses; three or four gaps are evident at category 2 synapses; five or more
gaps are evident at category 3 synapses. AChR-
ß3F/3F mice have fewer category 1 synapses and more
category 3 synapses than wild-type mice. Wild type: 40 category 1 synapses, 16
category 2 synapses, 3 category 3 synapses;
AChR-ß3F/3F: 11 category 1 synapses, 26
category 2 synapses, 18 category 3 synapses; P<0.005,
2 test. (K-N) Ultrastructural analysis of wild-type and
AChR-ß3F/3F mice. (K,L) Presynaptic nerve
terminals in wild-type (K) and AChR-ß3F/3F
(L) mice are filled with synaptic vesicles and are apposed by postjunctional
folds. Scale bar: 500 nm. (M,N) The postsynaptic membrane in wild-type (M) and
AChR-ß3F/3F (N) mice is electron dense at
the tops of the postjunctional folds (arrows). Scale bar=500 nm. (O)
The number of total postjunctional folds and the fold index are normal in
AChR-ß3F/3F mice, but the number of
openings, or mouths, to the synaptic cleft is reduced in
AChR-ß3F/3F mice. Number of total
postjunctional folds: wild type, 0.69±0.04 folds/µm, n=57;
AChR-ß3F/3F, 0.70±0.03 folds/µm,
n=75; P>0.05, unpaired t-test. The fold index:
wild type, 4.5±0.2, n=57;
AChR-ß3F/3F, 4.2±0.2%,
n=75; P>0.05, unpaired t-test. The number of
postjunctional fold mouths: wild type, 0.38±0.02 mouths/µm,
n=57; AchR-ß3F/3F, 0.24±0.01
mouths/µm, n=75; P<0.005. (P,Q) A model
to illustrate the organization of postjunctional folds in wild-type (P) and
AChR-ß3F/3F (Q) mice. In
AChR-ß3F/3F mice, the number of
postjunctional folds, lined with basal lamina, is normal, but fewer
postjunctional folds have mouths that open to the synaptic cleft; as a
consequence, the number of AChR striations is reduced in AChR-
ß3F/3F mice (E,F versus G,H).
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