Fig. 2. Synaptic size and AChR density are reduced in AChR-ß^3F/3F mice. Whole mounts of diaphragm muscle from P0 (A) and P30 (C) AChR- ß^3F/3F and wild-type mice were stained with Alexa Fluor 594--BGT to label AChRs and antibodies to neurofilament and synaptophysin (NF-Syn) to label axons and nerve terminals, respectively. Scale bar: 10 µm. Quantification of AChR area, AChR density and total AChR content at synapses in P0 (B) and P30 (D) mice. (B) At P0, the synaptic AChR area but not AChR density is reduced in AChR-ß^3F/3F mice. AChR area: wild type, 100±4.7%, n=4; AChR-ß^3F/3F, 71.1±4.5%, n=6; P<0.005; AChR density: wild type, 100±5.2%, n=4; AChR-ß^3F/3F, 87.8±1.7%, n=6; P>0.05; total AChR content: wild type, 100±9.9%, n=4; AChR-ß^3F/3F, 61.4±5.5%, n=6; P<0.05. (D) At P30, the synaptic AChR area and AChR density are reduced in AChR-ß^3F/3F mice. AChR area: wild type, 100±8.6%, n=3; AChR-ß^3F/3F, 56.8±4.1%, n=5; P<0.05; AChR density: wild type, 100±6.3%, n=3; AChR- ß^3F/3F, 61.2±5.1%, n=5; P<0.05; total AChR content: wild type: 100±8.4%, n=3; AChR-ß^3F/3F, 34.0±3.3%, n=5; P<0.05. (E,F) Miniature end-plate potentials (mepps) were recorded from synapses in diaphragm muscles from P30 AChR-ß^3F/3F mice (F) and wild-type (E) littermates. (G) The mepp amplitude is significantly reduced in AChR-ß^3F/3F mice: wild type, 0.95±0.05 mV, n=35; AChR-ß^3F/3F, 0.68±0.04 mV, n=35; P<0.005. The frequency and rise-time of mepps are normal in AChR-ß^3F/3F mice. Frequency: wild type, 5.7±0.8 Hz, n=35; AChR-ß^3F/3F, 6.0±0.7 Hz, n=35; P>0.05; rise time: wild type, 2.7±0.1 ms, n=35; AChR-ß^3F/3F, 2.6±0.1 ms, n=35; P>0.05. All P values were calculated using an unpaired t-test.