Research Paper Volume 9, Issue 3 pp 880—899

Figure 4. Lower facilitation and higher synaptic depression associated with decreased vesicle density at 12MO lama4^-/- neuromuscular junctions in EDL muscle. (A) Sample traces of paired-pulse facilitation at 10 ms and 100 ms delay for 12MO WT and lama4^-/- NMJs. (B) Plot of facilitation ratio against paired-pulse delay times at 10 ms and 100 ms. (C) Representative EPPs recordings during 100 Hz stimulation for 1 s duration at 12MO WT and lama4^-/- NMJs. Estimation of RRP size was determined by plotting the y-axis (quantal content) over the x-axis (cumulative quantal content) and extrapolating the linear declining phase at x-axis. (D) RRP size, (E) quantal release during steady state plateau (m_ss), (F) quantal release during the first ten stimuli (m_Peak) and (G) ratio of m_ss to m_Peak measured between genotypes at 12MO. (H) Representative staining of synaptic vesicle 2 (SV2; green) with respect to postsynaptic AChRs endplate (red) at 12MO. Lama4^-/- NMJ clearly displayed lower degree of overlap between SV2 and postsynaptic AChRs endplate (as indicated by arrow heads) which was not observed in WT NMJ. Scale bar = 10 µm. (I) SV2/AChR volume ratio was measured across all ages investigated. The difference in SV2/AChR volume ratio between both genotypes was evident at 12MO (as indicated in red dashed line box). (B) n = 4, NMJs = 13-15 per genotype. (D-G), n = 4, NMJs = 12 for both genotypes. (I) n = 3, NMJs = 51-82 per genotype at each age group. Statistical analyses were performed using Student’s t-tests for (B, D-G, and I); values are presented as mean ± SEM (* P < 0.05, ** P < 0.01, *** P < 0.001, and ****P < 0.0001).